Co-reporter:Maja Ponikvar-Svet;Diana N. Zeiger
Structural Chemistry 2017 Volume 28( Issue 3) pp:889-899
Publication Date(Web):30 March 2017
DOI:10.1007/s11224-017-0944-9
The contents of issues 1 and 2 of Structural Chemistry from the calendar year 2016 are summarized in the present review. A brief thermochemical commentary and possible guidelines for future research have been added to the summary of each paper.
Co-reporter:Maja Ponikvar-Svet;Diana N. Zeiger
Structural Chemistry 2017 Volume 28( Issue 3) pp:879-887
Publication Date(Web):21 November 2016
DOI:10.1007/s11224-016-0883-x
The content of the special combined issue for Magdolna (Magdi) Hargittai for the calendar year 2015 is summarized in the current review of the journal Structural Chemistry. A brief thermochemical commentary is added to the summary of each paper.
Co-reporter:Maja Ponikvar-Svet;Diana N. Zeiger
Structural Chemistry 2017 Volume 28( Issue 4) pp:1265-1273
Publication Date(Web):03 June 2017
DOI:10.1007/s11224-017-0983-2
The contents of issues 3 and 4 of Structural Chemistry from the calendar year 2016 are summarized in the present review. A brief thermochemical commentary and possible guidelines for future research are added to the summary of each paper.
Co-reporter:Margarida S. Miranda, Darío J.R. Duarte, Joel F. Liebman
The Journal of Chemical Thermodynamics 2016 Volume 97() pp:261-263
Publication Date(Web):June 2016
DOI:10.1016/j.jct.2016.02.004
There are two contemporary conflicting, indeed, incompatible determinations of measurements of the enthalpies of combustion and of formation of pyrazine-2-carboxylic acid in the literature, (−2268.0 ± 0.9 and −271.2 ± 1.1 kJ · mol−1) and (−2211.4 ± 0.9 and −327.8 ± 1.1 kJ · mol−1). The current paper discusses these two sets of values and from the use of a measurement of the enthalpy of sublimation, a newly evaluated enthalpy of formation of pyrazine itself, and of the quantum chemical calculations at the G3(MP2)//B3LYP level, the former results are accepted and the derived gas phase enthalpy of formation, −(167.6 ± 3.1) kJ · mol−1, suggested.
Co-reporter:Darío J. R. Duarte;Margarida S. Miranda
Structural Chemistry 2016 Volume 27( Issue 6) pp:1743-1751
Publication Date(Web):2016 December
DOI:10.1007/s11224-016-0794-x
In this work, we investigate the nature of the O–O and O–N interactions in protonated 1,2-dioxirane-3-one derivatives and protonated 1,2-oxaziridine-3-one derivatives, respectively. The quantum theory of atoms in molecules and the natural bond orbital (NBO) method in conjunction with the localized molecular orbital energy decomposition analysis (LMOEDA) have been used. LMOEDA and NBO analyses reveal that the O–O and O–N interactions exhibit characteristics of dative covalent bonds. In addition, the L(r) = −∇2ρ(r) function reveals that the O–O and O–N interactions can be categorized as strong hole–lump interactions.
Co-reporter:Alireza Fattahi, Joel F. Liebman, Margarida S. Miranda, Victor M.F. Morais, M. Agostinha R. Matos, Lev Lis, Steven R. Kass
International Journal of Mass Spectrometry 2015 Volume 378() pp:175-179
Publication Date(Web):15 February 2015
DOI:10.1016/j.ijms.2014.07.042
•Indenone's heat of hydrogenation was measured via two ion thermodynamic cycles.•High level G3 computations afford ΔHf° for cyclopentadienone (1) and indenone (2).•Both 1 and 2 are 4n π electron systems but are nonaromatic not antiaromatic.The heat of hydrogenation of indenone was measured via two partially independent thermodynamic cycles by carrying out energetic measurements (i.e., electron affinities, proton affinities and ionization potentials) on both negative and positive ions (ΔH°H2 = 17.8 ± 5.5 and 17.5 ± 5.7 kcal mol−1, respectively). High level G3 computations were also carried out to provide the heats of formation of indenone (16.8 kcal mol−1) and cyclopentadienone (14.0 kcal mol−1). These 4n π electron systems are found to be nonaromatic in contrast to previous views. A recent report on cyclopropenyl anion (J. Org. Chem. 2013, 78, 7370–7372) indicates that this ion is also nonaromatic, and suggests that NMR ring currents and nucleus independent chemical shift (NICS) calculations do not correlate with the energetic criterion for antiaromatic compounds.
Co-reporter:Alireza Fattahi, Joel F. Liebman, Margarida S. Miranda, Victor M.F. Morais, M. Agostinha R. Matos, Lev Lis, Steven R. Kass
International Journal of Mass Spectrometry 2014 Volume 369() pp:87-91
Publication Date(Web):15 August 2014
DOI:10.1016/j.ijms.2014.06.011
•Indenone’s heat of hydrogenation was measured via two ion thermodynamic cycles.•High level G3 computations afford ΔHf° for cyclopentadienone (1) and indenone (2).•Both 1 and 2 are 4n π electron systems but are nonaromatic not antiaromatic.The heat of hydrogenation of indenone was measured via two partially independent thermodynamic cycles by carrying out energetic measurements (i.e., electron affinities, proton affinities and ionization potentials) on both negative and positive ions (ΔH°H2 = 17.8 ± 5.5 and 17.5 ± 5.7 kcal mol−1, respectively). High level G3 computations were also carried out to provide the heats of formation of indenone (16.8 kcal mol−1) and cyclopentadienone (14.0 kcal mol−1). These 4n π electron systems are found to be nonaromatic in contrast to previous views. A recent report on cyclopropenyl anion (J. Org. Chem. 2013, 78, 7370–7372) indicates that this ion is also nonaromatic, and suggests that NMR ring currents and nucleus independent chemical shift (NICS) calculations do not correlate with the energetic criterion for antiaromatic compounds.
Co-reporter:Margarida S. Miranda, James S. Chickos, Joaquim C.G. Esteves da Silva, Joel F. Liebman
The Journal of Chemical Thermodynamics 2014 Volume 73() pp:69-75
Publication Date(Web):June 2014
DOI:10.1016/j.jct.2013.10.003
Highlights•Enthalpies of formation and sublimation of solid indigo at 298 K are presented.•B3LYP/6-311++G(d, p) DFT calculations are reported for the enthalpy of formation of indigo.•A consistent value is reported for the standard gas phase enthalpy of formation of indigo.The enthalpy of formation of indigo, as a solid, was reported in 1893. The enthalpy of sublimation at a mean temperature of 577 K (ca. 298 °C) was reported some 90 years later, and corrected herein to 298 K. These values were summed to result in a standard gas phase enthalpy of formation. We have also performed quantum chemical calculations at the B3LYP/6-311++G(d, p) level and analyzed them using (not quite) isodesmic and isomerisation reactions. From these disparate calorimetric and computational approaches, we hereby present a recommended enthalpy of formation of gaseous indigo of (35 ± 16) kJ · mol−1.
Co-reporter:Mohamed Maatallah, Min Guo, Driss Cherqaoui, Abdellah Jarid, Joel F. Liebman
International Journal of Hydrogen Energy 2013 Volume 38(Issue 14) pp:5758-5767
Publication Date(Web):10 May 2013
DOI:10.1016/j.ijhydene.2013.03.015
•Valuation of the clusters of 13th group elements for hydrogen storage.•The alanes AlnHm clusters have significant capability in producing energy.•Bare Aln clusters (n = 5, 6 and 7) are strong hydrogen acceptors.•AlnHm oxidation produce clean energy with harmless wastes.Bare and hydrogenated aluminium clusters Aln (n = 5–7) are studied using density functional theory in order to evaluate the ability to store molecular hydrogen and to estimate the energy release upon combustion with the aim to understand these species as alternative fuel resources. Six sequential molecular hydrogenations are considered and are shown to occur without or very low activation barriers. The H2 molecule uses its occupied σ orbital to react with an appropriate electron-deficient site of the cluster; this is generally followed by H migration leading to the favoured geometry. The combustion process produces alumina (Al2O3), water and a significant quantity of energy. The exothermicity seems to be largely independent of cluster size but it depends instead on the stored hydrogen quantity.
Co-reporter:Margarida S. Mira;Joaquim C. G. Esteves da Silva;Alvaro Castillo;Aaron T. Frank;Alexer Greer;Jodian A. Brown;Brittny C. Davis
Journal of Physical Organic Chemistry 2013 Volume 26( Issue 8) pp:613-625
Publication Date(Web):
DOI:10.1002/poc.3140
We have performed high level ab initio quantum mechanical calculations for aminoethene and the three isomeric 1,1- (Z)- or (E)-1,2-diaminoethenes as well as their singly and doubly charged cations derived by loss of electrons and/or upon protonation. Gas phase molecular structures were computed at the MP2/6-311 + G(3df,2p) level. Standard molar enthalpies of formation in the gas phase, at T = 298.15 K, were estimated using the G3 composite method and atomization, isodesmic and homodesmotic reactions. Other energetic parameters were also calculated at the G3 level: proton affinities, basicities and adiabatic ionization enthalpies.
Theoretical and experimental data are compared. The reported experimental data refer only to aminoethene wherein the standard molar enthalpy of formation has a considerable uncertainty, although the molecular structure is well established. There are no such data, neither structural nor thermochemical, for any of the three isomeric diaminoethenes. Isoelectronic comparisons are made. For example, the diprotonated diaminoethenes are isoelectronic to isobutene and (Z)- and (E)-butene, while the doubly ionized diaminoethenes are likewise related to trimethylenemethane and 1,3-butadiene. Copyright © 2013 John Wiley & Sons, Ltd.
Co-reporter:Margarida S. Miranda;Joaquim C. G. Esteves da Silva;Chi Hon
Structural Chemistry 2013 Volume 24( Issue 6) pp:1829-1839
Publication Date(Web):2013 December
DOI:10.1007/s11224-013-0237-x
We have performed high level ab initio quantum chemical calculations for 2- and 3-pyrrolidinone; tetrahydro-2- and -3-furanone; 2-, 3-, and 4-piperidinone; and tetrahydro-2-, -3-, and -4-pyranone. The most stable molecular structures were obtained from DFT calculations using the B3LYP density functional and the 6-31G(d) and 6-311+G(3df,2p) basis sets. The respective enthalpies of formation have been computed by the G3(MP2)//B3LYP composite method and appropriately chosen reactions. The calculated results are in excellent agreement with experimental data reported in the literature.
Co-reporter:Errol Lewars
Structural Chemistry 2013 Volume 24( Issue 3) pp:741-744
Publication Date(Web):2013 June
DOI:10.1007/s11224-012-0160-6
Acrolein (propenal) is a ubiquitous compound in the global environment with diverse deleterious ramifications for human health. Despite its importance, its measured enthalpy of formation is still contentious. Using high level quantum chemical calculations, we recommend a consensus value of −65 ± 3 kJ mol−1 for the gas phase species. Comparison is made with the other “acrylo” species, acrylonitrile and acrylic acid, and to other conjugated species such as butadiene and crotonaldehyde.
Co-reporter:Joel F. Liebman;James S. Chickos;Rafael Notario
Structural Chemistry 2013 Volume 24( Issue 6) pp:1785-1787
Publication Date(Web):2013 December
DOI:10.1007/s11224-013-0363-5
This essay is the introductory paper for a special issue of Structural Chemistry explicitly dedicated to the premier Spanish calorimetrist and thermochemist, our colleague and friend, María Victoria Roux. The studies in this issue were written on the occasion of her recent retirement from the CSIC Institute of Physical Chemistry “Rocasolano,” Madrid.
Co-reporter:Aimé Kayembe, Errol Lewars, Joel F. Liebman
The Journal of Chemical Thermodynamics 2012 Volume 52() pp:43-56
Publication Date(Web):September 2012
DOI:10.1016/j.jct.2012.03.007
Quinones of bicyclo[3.1.0]hexa-1,3,5-triene were examined computationally. The six compounds considered were the five possible classical and one non-classical quinone: bicyclo[3.1.0]hexa-1(6),4-diene-2,3-dione (and its monocyclic isomer with a long trans-annular bond), bicyclo[3.1.0]hexa-1(5),3-diene-2,6-dione, bicyclo[3.1.0]hexa-1,4-diene-3,6-dione (and its monocyclic isomer with a long trans-annular bond), and bicyclo[3.1.0]hexa-1(5),4-diene-2,4-dione-3,6-diyl, a non-classical (non-Kekulé) zwitterion. The two long trans-annular bond structures are akin to that found for m-benzyne. Geometries were calculated (BLYP/6-31G∗, CASSCF(2,2)/6-31G∗, MP2/6-31G∗) and electronic structural inferences were made from the geometries. Also calculated were relative energies and heats of formation (CBS-QB3), singlet and triplet energies (BLYP/6-31G∗), and ionization energies and electron affinities (HF/6-311+G∗∗//BLYP/6-31G∗). The NICS(1) calculations were performed as a probe of the aromaticity of the diverse quinones.Graphical abstractHighlights► Five new bicyclo[3.1.0]hexa-1,3,5-triene quinones are explored quantum chemically. ► A nonclassical zwitterionic quinone of reasonable stability is uncovered. ► Shortbond-long bond isomerism is exhibited.
Co-reporter:Margarida S. Miranda, M. Agostinha R. Matos, Victor M.F. Morais, Joel F. Liebman
The Journal of Chemical Thermodynamics 2011 Volume 43(Issue 5) pp:635-644
Publication Date(Web):May 2011
DOI:10.1016/j.jct.2010.11.006
The present work reports an experimental and computational study of the energetics of 1,2-benzisothiazol-3(2H)-one and 1,4-benzothiazin-3(2H, 4H)-one. The standard (p° = 0.1 MPa) massic energy of combustion, at T = 298.15 K, of each compound was measured by rotating bomb combustion calorimetry, in oxygen that allowed the calculation of the respective standard molar enthalpy of formation, in the condensed phase, at T = 298.15 K. The standard molar enthalpies of sublimation, at T = 298.15 K, were measured by high-temperature Calvet microcalorimetry. From the combination of data obtained by both techniques we have calculated the standard molar enthalpies of formation, in the gaseous phase, at T = 298.15 K. In addition, computational calculations were carried using the density functional theory with the B3LYP functional and the 6-31G∗ basis set and some correlations between structure and energetics were obtained for the keto and enol forms of both compounds. Using the G3(MP2)//B3LYP composite method and various appropriate reactions, the standard molar enthalpies of formation of 1,2-benzisothiazol-3(2H)-one and 1,4-benzothiazin-3(2H, 4H)-one, at T = 298.15 K, were computationally derived and compared with the experimental data. The aromaticity of 1,2-benzisothiazol-3(2H)-one, 1,4-benzothiazin-3(2H, 4H)-one and that of some related species was evaluated by analysis of nucleus independent chemical shifts (NICS).Research highlights► The standard molar enthalpies of formation and sublimation of 1,2-benzisothiazol-3(2H)-one and 1,4-benzothiazin-3(2H, 4H)-one were determined. ► Computational calculations predict that keto tautomers are more stable than the enol ones. ► G3(MP2)//B3LYP calculations allowed estimation of the standard enthalpies of formation. ► The aromaticity of both compounds was evaluated by analysis of NICS values.
Co-reporter:Margarida S. Miranda, M. Agostinha R. Matos, Victor M.F. Morais, Joel F. Liebman
The Journal of Chemical Thermodynamics 2011 Volume 43(Issue 3) pp:364-370
Publication Date(Web):March 2011
DOI:10.1016/j.jct.2010.10.009
A study on the molecular structure and energetics of 10,11-dihydro-5H-dibenzo[a,d ]cycloheptene (dibenzosuberane) was performed combining experimental calorimetric techniques and high level computational calculations. In the experimental work, the solid phase standard (p∘p∘ = 0.1 MPa) molar enthalpy of formation of 10,11-dihydro-5H-dibenzo[a,d]cycloheptene was derived from its standard massic energy of combustion, at T = 298.15 K, measured by static bomb combustion calorimetry, in oxygen. The respective standard molar enthalpy of sublimation, at T = 298.15 K, was measured by Calvet microcalorimetry enabling the calculation of the standard molar enthalpy of formation (161.4 ± 3.7) kJ · mol−1, in the gaseous phase, at T = 298.15 K. In addition, computational calculations were performed using the density functional theory with the B3LYP hybrid functional and extended basis sets in order to obtain the molecular structure of 10,11-dihydro-5H-dibenzo[a,d]cycloheptene and that of related molecules. Estimates of the standard molar enthalpy of formation, in the gaseous phase, at T = 298.15 K, for 10,11-dihydro-5H-dibenzo[a,d]cycloheptene were performed using three different methods: G3(MP2)//B3LYP, MC3BB, and MC3MPW and appropriate homodesmic reactions. Computational estimates are in very good agreement with the experimental value.
Co-reporter:Margarida S. Miranda;M. Agostinha R. Matos;Victor M. F. Morais
Structural Chemistry 2011 Volume 22( Issue 6) pp:
Publication Date(Web):2011 December
DOI:10.1007/s11224-011-9812-1
Aromaticity is of continuing interest to the organic chemical community. We recently presented a model for the aromaticity of carbocyclic and heterocyclic derivatives of indane and indene, i.e. species defined as benzenes fused to 5-membered rings. The current note extends this model to related derivatives of tetralin and naphthalene, benzenes fused to 6-membered rings. Explicit species discussed herein are: benzopyran, both α- and β-tetralone, coumarin and quinoline.
Co-reporter:Margarida S. Miranda, M. Agostinha R. Matos, Victor M. F. Morais, and Joel F. Liebman
The Journal of Physical Chemistry B 2011 Volume 115(Issue 20) pp:6616-6622
Publication Date(Web):May 4, 2011
DOI:10.1021/jp2011149
This paper reports an experimental and computational study on the energetics of 1,2,3-benzotriazin-4(3H)-one. The standard (p° = 0.1 MPa) molar enthalpy of formation of solid 1,2,3-benzotriazin-4(3H)-one, at T = 298.15 K, was derived from its standard massic energy of combustion measured by static bomb combustion calorimetry in oxygen. The Calvet high-temperature vacuum sublimation technique was used to measure the respective standard molar enthalpy of sublimation at T = 298.15 K. From these two experimentally determined thermodynamic parameters, we have calculated the standard molar enthalpy of formation of 1,2,3-benzotriazin-4(3H)-one in the gas phase at T = 298.15 K, (200.9 ± 3.8) kJ·mol–1. Interrelations between structure and energy for 1,2,3-benzotriazin-4(3H)-one, the tautomer 1,2,3-benzotriazin-4(1H)-one, and the enol tautomer 1,2,3-benzotriazin-4-ol were discussed based on density functional theory (DFT) calculations with the B3LYP hybrid functional and the 6-311++G(d,p) basis set. The gas-phase enthalpy of formation of 1,2,3-benzotriazin-4(3H)-one was estimated from quantum chemical calculations using the G3(MP2)//B3LYP composite method. Nucleus-independent chemical shifts (NICS) were also calculated with the purpose of analyzing the aromaticity of the benzenic and heterocyclic rings of the title molecule and others related tautomerically to it.
Co-reporter:Maria Victoria Roux, Gloria Martín-Valcarcel, Rafael Notario, Sandeep Kini, James S. Chickos, and Joel F. Liebman
Journal of Chemical & Engineering Data 2011 Volume 56(Issue 4) pp:1220-1228
Publication Date(Web):February 7, 2011
DOI:10.1021/je101124p
This study is a multidisciplinary contribution to the thermochemistry of 1,4-cubanedicarboxylic acid (pentacyclo[4.2.0.02,5.03,8.04,7]octane-1,4-dicarboxylic acid). An isoperibolic static microbomb calorimeter was used to determine the enthalpy of formation in the condensed phase at T = 298.15 K as ΔfHm°(cr) = (−355.9 ± 11.7) kJ·mol−1. The enthalpy of sublimation was obtained by combining the vaporization enthalpy evaluated by correlation-gas chromatography and the fusion enthalpy measured by differential scanning calorimetry and adjusted to T = 298.15 K, which afforded the value ΔsubHm(298.15 K) = (126.5 ± 9.0) kJ·mol−1. Combination of these two enthalpies gave ΔfHm°(g, 298.15 K) = (−229.4 ± 14.8) kJ·mol−1. Additionally the enthalpy of sublimation of 1-adamantanecarboxylic acid (tricyclo[3.3.1.13,7]decane-1-carboxylic acid) was determined as ΔsubHm(298.15 K) = (98.7 ± 4.5) kJ·mol−1. By means of theoretical calculations using isodesmic reactions, the enthalpy of formation of 2,6-cuneanedicarboxylic acid (pentacyclo[3.3.0.02,4.03,7.06,8]octane-2,6-dicarboxylic acid) was calculated. Strain energies of cubane and cuneane dicarboxylic acids were also calculated.
Co-reporter:Maria Victoria Roux, Manuel Temprado, Pilar Jiménez, and Rafael Notario, Archana R. Parameswar, Alexei V. Demchenko, and James S. Chickos , Carol A. Deakyne and Joel F. Liebman
Journal of Chemical & Engineering Data 2011 Volume 56(Issue 12) pp:4725-4732
Publication Date(Web):September 26, 2011
DOI:10.1021/je200549z
In a continuation of our investigations of the thermochemistry of heterocyclic ring systems and sulfur-containing compounds, the standard molar enthalpy of formation of tetrahydro-2H-1,3-oxazine-2-thione (CAS no. 17374-18-4) at T = 298 K has been evaluated both experimentally and computationally. Combined enthalpies of combustion and sublimation, measured by rotary bomb combustion calorimetry and the Knudsen effusion technique, yielded a gas-phase enthalpy of formation of −(104.0 ± 5.5) kJ·mol–1. The G3 value of −104.6 kJ·mol–1 calculated using an isodesmic bond separation reaction is in excellent agreement with the experimental result. The variation in enthalpy of formation with ring size is discussed, and the G3 enthalpy of formation of tetrahydro-2H-1,3-thiazine-2-thione (72.4 kJ·mol–1) was also computed for this purpose.
Co-reporter:Henry A. Bent
Structural Chemistry 2011 Volume 22( Issue 2) pp:371-372
Publication Date(Web):2011 April
DOI:10.1007/s11224-010-9726-3
It is well established that the σ-bond in the elemental halogens is weak. It is likewise weak in peroxides, disulfides, interhalogens, noble gas monohalide cations, and other isoelectronic species. This is normally explained in terms of lone pair–lone pair repulsion. Other explanations are given as well.
Co-reporter:Maja Ponikvar-Svet
Structural Chemistry 2011 Volume 22( Issue 5) pp:
Publication Date(Web):2011 October
DOI:10.1007/s11224-011-9849-1
In the current review of the journal Structural Chemistry, the content of the first three issues for the calendar year 2011 is related to thermochemistry. Each paper is summarized and followed by a short thermochemical comment.
Co-reporter:Maja Ponikvar-Svet;Loryn R. Keating;Bryan J. Dodson
Structural Chemistry 2010 Volume 21( Issue 3) pp:527-540
Publication Date(Web):2010 June
DOI:10.1007/s11224-010-9583-0
In the current review, the content of the journal Structural Chemistry for the calendar year 2005 is related to thermochemistry. Papers are summarized and a thermochemical flavor added. Often questions are asked and research topics suggested.
Co-reporter:Rafael Notario;Maria Victoria Roux
Structural Chemistry 2010 Volume 21( Issue 3) pp:481-484
Publication Date(Web):2010 June
DOI:10.1007/s11224-009-9574-1
Acrylonitrile is a key industrial compound with numerous uses. Despite its importance, its enthalpy of formation is still contentious. There is a 12 kJ mol−1 range of values reported for the gas phase quantity: 173–185 kJ mol−1. Quantum chemical calculations, using current methodologies and defining reactions, suggest values between 185 and 191 kJ mol−1: the recommended value, an average, is 188 ± 7 kJ mol−1.
Co-reporter:Thomas M. Klapötke
Structural Chemistry 2010 Volume 21( Issue 5) pp:1051-1052
Publication Date(Web):2010 October
DOI:10.1007/s11224-010-9644-4
In a further attempt to understand the interplay of structure and energy of compounds containing nitro groups, the enthalpies of formation of corresponding species with trinitromethyl and trimethylmethyl (t-butyl) groups are compared.
Co-reporter:Margarida S. Miranda, M. Agostinha R. Matos, Victor M.F. Morais, Joel F. Liebman
The Journal of Chemical Thermodynamics 2010 Volume 42(Issue 9) pp:1101-1106
Publication Date(Web):September 2010
DOI:10.1016/j.jct.2010.04.006
An experimental and computational thermochemical study was performed for oxindole. The standard (p∘=0.1MPa) molar enthalpy of formation of solid oxindole was derived from the standard molar energy of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The respective standard molar enthalpy of sublimation, at T = 298.15 K, was measured by Calvet microcalorimetry. The standard molar enthalpy of formation in the gas phase was derived as −(66.8 ± 3.2) kJ · mol−1.Density functional theory calculations with the B3LYP hybrid functional and the 6-31G∗ and 6-311G∗∗ sets have also been performed in order to obtain the most stable conformation of oxindole. A comparison has been made between the structure of oxindole and that of the related two-ring molecules: indoline and 2-indanone and the one-ring molecules: pyrrolidine and 2,3-dihydropyrrole. The G3(MP2)//B3LYP method and appropriate reactions were used to obtain estimates of the standard molar enthalpy of formation of oxindole in the gas phase, at T = 298.15 K. Computationally obtained estimates of the enthalpy of formation of oxindole are in very good agreement with the experimental gas phase value. The aromaticity of oxindole was evaluated through the analysis of the nucleus independent chemical shifts (NICS) obtained from the B3LYP/6-311G∗∗ wave functions.
Co-reporter:Margarida S. Miranda, Victor M.F. Morais, M. Agostinha R. Matos, Joel F. Liebman
The Journal of Chemical Thermodynamics 2010 Volume 42(Issue 9) pp:1094-1100
Publication Date(Web):September 2010
DOI:10.1016/j.jct.2010.04.007
The energetics of 1-benzosuberone was studied by a combination of calorimetric techniques and computational calculations.The standard (p° = 0.1 MPa) molar enthalpy of formation of 1-benzosuberone, in the liquid phase, was derived from the massic energy of combustion, in oxygen, at T = 298.15 K, measured by static bomb combustion calorimetry. The standard molar enthalpy of vaporization, at T = 298.15 K, was measured by Calvet microcalorimetry. From these two parameters the standard (p° = 0.1 MPa) molar enthalpy of formation, in the gaseous phase, at T = 298.15 K, was derived: −(96.1 ± 3.4) kJ · mol−1. The G3(MP2)//B3LYP composite method and appropriate reactions were used to computationally calculate the standard molar enthalpy of formation of 1-benzosuberone, in the gaseous phase, at T = 298.15 K. The computational results are in very good agreement with the experimental value.
Co-reporter:Carol A. Deakyne, Haunani M. Thomas, Joel F. Liebman
Journal of Fluorine Chemistry 2009 Volume 130(Issue 9) pp:836-845
Publication Date(Web):September 2009
DOI:10.1016/j.jfluchem.2009.07.006
In the current paper, we discuss our high level quantum chemical results for the structure and energetics of triplet (and hence open-shell) isomers corresponding to the stoichiometry of one boron, carbon, and fluorine apiece, and two hydrogens. While partially bond-ruptured excited ketene- and diazomethane-like H2C–B–F and the carbene H(F)B–C–H plausibly emerge as the most stable isomers, a variety of novel structural features emerge for the assembled energy minima of at least 16 species. All of these species are compared as well as transition states that connect them. Comparison is made with corresponding forms of the singlet species with this stoichiometry, shown earlier by us to have a rich diversity of structures as well as a large range of energies and relative stabilities.Transition structures connecting the three most stable minima on the [B, C, F, H2] triplet potential energy surface.
Co-reporter:James S. Chickos
Structural Chemistry 2009 Volume 20( Issue 6) pp:
Publication Date(Web):2009 December
DOI:10.1007/s11224-009-9511-3
We ask the question, “In the absence of intermolecular interactions, when are ideal gases not ideal?” We find two cherished equations become problematic when the size of the molecule becomes too big or its mass is too small.
Co-reporter:Dmitri Lipkind;James S. Chickos
Structural Chemistry 2009 Volume 20( Issue 4) pp:617-618
Publication Date(Web):2009 August
DOI:10.1007/s11224-009-9452-x
Vaporization enthalpies for the isomeric diazines were discussed within the context of recent measurements and estimation techniques. It is suggested that pyridazine shows enigmatic behavior.
Co-reporter:Maja Ponikvar-Svet
Structural Chemistry 2009 Volume 20( Issue 5) pp:757-765
Publication Date(Web):2009 October
DOI:10.1007/s11224-009-9476-2
We continue our use of “simple” energetic patterns, where simple means the use of parameters derived only from the stoichiometry of these species in our studies of the entropy of formation (TΔfSo) of aqueous anions. Relationships between the entropy of formation and different parameters such as the number of oxygen atoms, the natural logarithm of the molecular weight and the total number of atoms are explored. The charge of the species, z− continues to be explicitly considered where we now explore various choices of p and use of zp as a parameter.
Co-reporter:H. Donald B. Jenkins;Maja Ponikvar
Structural Chemistry 2009 Volume 20( Issue 1) pp:31-35
Publication Date(Web):2009 February
DOI:10.1007/s11224-008-9402-z
It is found that there is a nearly constant difference between the normalized values of the heat capacities and standard entropies of potassium and ammonium ion salts in the condensed phase, both solid salts and their aqueous solutions. Extension to the free gaseous ions remains moot.
Co-reporter:Maja Ponikvar-Svet
Structural Chemistry 2009 Volume 20( Issue 6) pp:1019-1037
Publication Date(Web):2009 December
DOI:10.1007/s11224-009-9506-0
In the current study we relate the contents of the journal of “Structural Chemistry” for the calendar year 2006 to thermochemistry. Each paper is briefly summarized and supplemented by a comment which explicitly interrelates the content of the study to chemical energetics.
Co-reporter:H. Donald B. Jenkins and Joel F. Liebman
Journal of Chemical & Engineering Data 2009 Volume 54(Issue 2) pp:351-358
Publication Date(Web):November 14, 2008
DOI:10.1021/je800414d
The ever-growing requirement to develop new materials for highly specific applications is making major demands for thermodynamic data which have not, to date, been measured. This, in turn, means that, increasingly, estimated values are required to make thermodynamic interpretations and feasibility studies of reactions involving these materials. In this vein, four further extensions of, and insights into, the Thermodynamic Solvate Difference Rule, are presented here and tested. The result is the provision of valuable, albeit approximate, rules useful for many areas of organic/inorganic chemisty to predict thermodynamic data in cases where experimental data have not yet been determined. These extended rules take the form where j + k = d + s and the salt M′pX′q can be the same as MpXq. P represents any of the individual thermodynamic properties: ΔfH°, ΔfG°, ΔfS°, S°, etc. Also For salts MpXq, M′pX′q, and M′rX′s and then for multiple salts compounded from these, where one salt is considered to be the “solvent” of the other, and vice-versa, then where ΘP{M′rX′s, s−s} and ΘP{MpXq,s−s} are constants, independent of the nature of MpXq and M′rX′s, respectively. Thus, salts may be permuted as being regarded as solvent and solvate. A cascading rule can be established as follows and permutations thereon. Developed and applied initially for inorganic compounds, the rule is shown to extend into the arena of organic thermochemistry.
Co-reporter:Dmitry Ponomarev, Viatcheslav Takhistov, Suzanne Slayden, Joel Liebman
Journal of Molecular Structure 2008 Volume 876(1–3) pp:15-33
Publication Date(Web):30 March 2008
DOI:10.1016/j.molstruc.2007.05.038
General trends in thermochemistry for free radicals as the fragments of halogenated molecules of main group elements were found for the first time applying the series of isodesmic (working) reactions following the Benson’s comparison of relative stabilities of free radicals in equations R+R′H→RH+R′+Q, where Q is stabilization (destabilization) energy. The enthalpies of formation for parent molecules of main group elements’ halogenides necessary for application of this and similar equations were presented earlier [A.V. Golovin, V.V. Takhistov, J. Mol. Struct., 784 (2006) 47.].For fluorinated free radicals EF (E = Be–Ra), EF2 (EHF) (E = B–Tl, N–Bi) and EF3 (EH2F, EHF2) (E = C–Pb) the gradual decrease in stabilization by fluorine atoms was found when coming down the periodic table. This turned to destabilization for Tl, Sb, and Bi, and IVth group of elements (excluding carbon) with increasing destabilization in the row Si < Ge < Sn < Pb. The destabilization of free radicals by other halogens for IVth group of elements decreased in the row F > Cl > Br > I which was interpreted by involvement of polarizability (PAZ) effect of halogens increasing in this direction. For finding the enthalpies of formation for silicon and germanium-centered free radicals the data on ν ≡ E–H frequencies in IR-spectra were applied. Quite definite tendencies in structure/enthalpy of formation interrelationship were found for chlorinated, brominated and iodinated free radicals of IInd and IIIrd group of elements.In the VIth group the situation with F → Cl → Br → I replacement in stabilization of free radical center appeared completely different compared with II–IV groups. Owing to the high electronegativity of HO-group and low thermodynamic stability of HO radical all halogens highly stabilize OX radical and perform it in the row F < Cl–Br < I which is explained by increase of PAZ effect in this direction. All halogens are suggested to stabilize other EX free radicals (E = S–Po) but essentially less compared with OX free radicals. The tendencies in stabilization/destabilization for Vth group free radicals appeared to be intermediate between those for IVth and VIth groups.
Co-reporter:Dmitry Ponomarev, Viatcheslav Takhistov, Suzanne Slayden, Joel Liebman
Journal of Molecular Structure 2008 Volume 876(1–3) pp:34-55
Publication Date(Web):30 March 2008
DOI:10.1016/j.molstruc.2007.05.040
General trends in thermochemistry of bi- and triradicals as the fragments of halogenated molecules of main group elements :EX (:EHX; :EX2) and triradicals ·:EX, respectively, where X-halogens F–I were found for the first time.The enthalpy of formation for methylene CH2 was drastically changed in present work with adopted values 79 (3B1) and 88 (1A1) compared with currently used values ∼93 and ∼102 kcal mol−1, respectively. This happened mainly because of the drastic change in the enthalpy of formation for ketene CH2CO molecule from currently used value −11.4 to −24 kcal mol−1 [A.V. Golovin, D.A. Ponomarev, V.V. Takhistov, This Journal 524 (2000) 259] which was the source of experimental determination of ΔHf0 :CH2. Other experimental data are provided for support of the lower values of the ΔHf0 for :CH2.It was established that halogens F–I stabilize all biradicals :EX (E = B–Tl, N–Bi) and :EHX (:EX2) (E = C–Pb) compared with the free radicals of these elements. This was interpreted by essentially smaller thermodynamic stability of bi- compared with mono (free)radicals the former extracting larger stabilization at H → X replacement from the same halogen compared with more stable free radicals. The expected increase in stabilization of biradicals is observed when coming down the periodic table while due to lower stability of biradicals all halogens reveal similar (contrary to free radicals) stabilization effects.Finding unknown values and correcting some literature data on the enthalpies of formation for mono-, bi- and triradicals we could estimate their thermodynamic stabilities. It was established that only about 40 molecules, radicals and biradicals from more than 800 hydrides and halogenides possess higher ΔHf0 values compared with their fragments with elements in lower valent states with H2 (rarely HX) as a partner. This might be treated only in the sense that the parent species are less stable than the system [fragment + H2 (or HX)] rather than as the support of the higher thermodynamic stability of an element in its lower valent state. The thermodynamic stability of such state may be found only by the comparison of the consecutive bond dissociation energies (BDEs) in parent molecules like PbH3X → ·PbH2X (BDE1) → :PbHX (BDE2) → ·:PbX (BDE3) and only if BDE2 < 0 one can declare the larger thermodynamic stability of element in lower valent state. But this does not happen with any species studied in this work. This means that thermodynamic stability quite definitely decreases in the row molecule > free radical > biradical > triradical > :E: (C–Pb) contrary to the current opinion of larger thermodynamic stability of lower valent states for, say, thallium or lead.The detailed analysis of many computational results related to thermochemistry of halogenated main group elements is performed with quite definite result that neither ab initio, DFT, semi-empirical methods (or their combination) can be trusted either in support of known or prediction of unknown values of the enthalpies of formation while the empirical approach, elaborated in this work, solves the problem of calculation of the enthalpies of formation and search of general trends in structure/enthalpy of formation for halogenated main group elements.
Co-reporter:Maja Ponikvar
Structural Chemistry 2008 Volume 19( Issue 6) pp:849-872
Publication Date(Web):2008 December
DOI:10.1007/s11224-008-9380-1
In this study, we relate the contents of the journal Structural Chemistry for the calendar year 2007 and thermochemistry. The year’s articles were briefly summarized and a thermochemical comment written to supplement them. Frequently questions were asked and future research was suggested.
Co-reporter:Maja Ponikvar
Structural Chemistry 2008 Volume 19( Issue 3) pp:501-508
Publication Date(Web):2008 June
DOI:10.1007/s11224-008-9310-2
Relationships between the entropy of formation (TΔfSo) of aqueous complex anions and simple parameters, such as negative value of the charge of the species, the number of oxygen atoms, the total number of atoms, the natural logarithm of the molecular weight, denticity, total number of anions in certain species, coordination number, and number of affixed waters were studied and discussed. Multivariate methods of analysis were used for identifying the chemometric similarities among different species.
Co-reporter:Alexander Greer
Structural Chemistry 2008 Volume 19( Issue 5) pp:817-818
Publication Date(Web):2008 October
DOI:10.1007/s11224-008-9369-9
The enthalpy of oxidative cleavage of azo compounds (diazenes) is discussed and compared with that of symmetric olefins. The roles of substituents and of electronegativity are explicitly discussed.
Co-reporter:Dipankar Roy, Chandan Patel, Joel F. Liebman and Raghavan B. Sunoj
The Journal of Physical Chemistry A 2008 Volume 112(Issue 37) pp:8797-8803
Publication Date(Web):August 26, 2008
DOI:10.1021/jp8041395
Although a large volume of experimental evidence is available on the existence of intramolecular nonbonding interactions between chalcogen atoms in main group organometallic compounds, the primary focus has been on the contact distances involving the chalcogen atoms. The important class of intramolecular Se···X (where X is O, S, N) nonbonding interaction in a series of organoselenium compounds is quantified using a new scheme based on a molecular property descriptor. In the present study, we have employed the nucleus-independent chemical shift [NICS(0)] values, as a property descriptor to evaluate the strength of exocyclic nonbonding interactions in a series of aryl selenides. The ab initio MP2 as well as density functional theory methods have been used in conjunction with Dunning’s cc-pVDZ basis set. The quantified values of Se···X nonbonding interactions are compared with other schemes based on thermochemical equations such as homodesmic and ortho−para methods. The changes in NICS(0) values at the aryl ring center are found to be sensitive to the strength of exocyclic Se···X interaction.
Co-reporter:Axel Schulz
Structural Chemistry 2008 Volume 19( Issue 4) pp:633-635
Publication Date(Web):2008 August
DOI:10.1007/s11224-008-9336-5
In this note, we briefly compare oxidation states associated with adjacent rows in the periodic table. Or more precisely, we make comparisons for a few compounds containing elements from the first two rows in which a given value of the quantum number “l” appears. We start with hydrogen and lithium, proceed through rows 2 and 3 of the main group elements, and then briefly discuss some transition metal chemistry. The discussion concludes with a contrast of the lanthanides and actinides.
Co-reporter:Yadu B. Tewari, David J. Vanderah, Michele M. Schantz, Robert N. Goldberg, J. David Rozzell, Joel F. Liebman, Raymond Wai-Man Hui, Yitzy Nissenbaum, Ahmad Reza Parniani
The Journal of Chemical Thermodynamics 2008 Volume 40(Issue 4) pp:661-670
Publication Date(Web):April 2008
DOI:10.1016/j.jct.2007.10.011
The equilibrium constants K for the ketoreductase-catalyzed reduction reactions of 1-benzyl-3-pyrrolidinone, ethyl 2-oxo-4-phenylbutyrate, ethyl 4-chloroacetoacetate, 1-benzyl-4-piperidone, and 1-benzyl-3-piperidone were measured in n-hexane at T = 298.15 K by using gas chromatography. The equilibrium constants for the reaction involving 1-benzyl-4-piperidone were also measured as a function of temperature (288.15 to 308.05) K. The calculated thermodynamic quantities for the reaction (1-benzyl-4-piperidone + 2-propanol = 1-benzyl-4-hydroxypiperidine + acetone) reaction carried out in n-hexane at T = 298.15 K are: K = (26.2 ± 1.7); ΔrGm∘=-(8.10±0.16)kJ·mol-1; ΔrHm∘=-(3.44±0.42)kJ·mol-1; and ΔrSm∘=(15.6±1.4)J·K-1·mol-1. The chirality of the hydroxyl products of the reactions , , and has also been investigated. The results showed that the stereoselectivity of the hydroxyl products formed can be controlled by the selection of the solvent and enzyme used in these reactions. The thermochemical results for these reactions are compared with the results for reactions that have analogous structural features as well as with the results of quantum chemical calculations.
Co-reporter:Carol A. Deakyne, Lisa K. Norton, Ashley M. Abele, Alicia K. Ludden, Joel F. Liebman
International Journal of Mass Spectrometry 2007 Volume 267(1–3) pp:324-337
Publication Date(Web):1 November 2007
DOI:10.1016/j.ijms.2007.03.005
Following thermochemical studies and the accompanying analysis in the calorimetric literature, in earlier computational and conceptual studies we investigated the systematics of the mean bond enthalpy ratio 〈Dm°(XY2)〉/Dm°(XY)〈Dm°(XY2)〉/Dm°(XY) for 16-valence electron neutral and ionic triatomic species. For neutral species wherein X is a group 14 element and Y is from group 16, the ratio was ca. 0.8 rising to ca. 0.9 for the corresponding anions with X from group 13, and falling to ca. 0.7 for the cations with X from group 15. Good agreement between theory and experiment was found where admittedly the majority of the data for the latter is for the neutral species. In the current study at the G2 computational level (and G3 for selected systems), the related asymmetric valence isoelectronic triatomic species YXZ are discussed and this pattern calculationally preserved. The results are in concurrence with the one experimentally available datum for comparison, namely from the literature measured value for the enthalpy of formation of OCS. Other surprises and systematics are discussed as well for what otherwise might have been superficially considered to be simple species, for these and related pentaatomic species of the type HYXYH.
Co-reporter:Joel F. Liebman;Zoltán Varga;Magdolna Hargittai
Structural Chemistry 2007 Volume 18( Issue 3) pp:269-271
Publication Date(Web):2007 June
DOI:10.1007/s11224-006-9127-9
The molecular geometries, relative stabilities, binding energies, and dissociation energies of NaDyBr4 and its molecular ion are discussed. Both the bidentate and tridentate isomers are stable for the neutral species, while only the bidentate form is stable for NaDyBr4+.
Co-reporter:Maja Ponikvar;H. Donald B. Jenkins
Structural Chemistry 2007 Volume 18( Issue 6) pp:883-889
Publication Date(Web):2007 December
DOI:10.1007/s11224-007-9189-3
Entropies of formation (\(T\Delta_{f}S^{0})\) of aqueous fluorine containing anions were shown to follow different entropic patterns than those of oxygen or hydrogen containing anions. Approaches to estimation of the entropies of formation of these anions are based on “simple” entropic patterns, where simple means the use of parameters derived only from the stoichiometry of these species, which are investigated, discussed and commented upon.
Co-reporter:Aaron T. Frank;Adebogun Adenike;David Aebisher;Alexander Greer
Structural Chemistry 2007 Volume 18( Issue 1) pp:71-74
Publication Date(Web):2007 February
DOI:10.1007/s11224-006-9126-x
Indigo is a unique organic compound in terms of its blue color and its multiple conjugated functional groups contained therein. We ask whether the enthalpy of its cleavage reaction into two isatin molecules reflects the novelty of either this color and/or the conjugated functionalities contained therein.
Co-reporter:Yadu B. Tewari, Joel F. Liebman, J. David Rozzell, David J. Vanderah, Michele M. Schantz
The Journal of Chemical Thermodynamics 2007 Volume 39(Issue 7) pp:1090-1097
Publication Date(Web):July 2007
DOI:10.1016/j.jct.2006.12.007
The equilibrium constants K for the ketoreductase-catalyzed reduction reactions (2-substituted cyclohexanone + 2-propanol = cis- and trans-2-substituted cyclohexanol + acetone) have been measured in n-hexane as solvent. The 2-substituted cyclohexanones included in this study are: 2-methylcyclohexanone, 2-phenylcyclohexanone, and 2-benzylcyclohexanone. The equilibrium constants K for the reactions with 2-methylcyclohexanone were measured over the range T = 288.15 to 308.05 K. The thermodynamic quantities at T = 298.15 K are: K = (2.13 ± 0.06); ΔrGm∘=-(1.87±0.06)kJ·mol-1; ΔrHm∘=-(6.56±2.68)kJ·mol-1; and ΔrSm∘=-(15.7±9.2)J·K-1·mol-1 for the reaction involving cis-2-methylcyclohexanol, and K = (10.7 ± 0.2); ΔrGm∘=-(5.87±0.04)kJ·mol-1; ΔrHm∘=-(2.54±1.8)kJ·mol-1; and ΔrSm∘=(11.2±6.4)J·K-1·mol-1 for the reaction involving trans -2-methylcyclohexanol. The standard molar Gibbs free energy changes ΔrGm∘ for the reactions (trans-2-substituted cyclohexanol = cis-2-substituted cyclohexanol) in n-hexane have also been calculated and compared with the literature data that pertain to reactions in the gas phase and at higher temperatures. Experiments carried out with a chiral column demonstrated that the enzymatic reduction of 2-phenylcyclohexanone catalyzed by the ketoreductase used in this study is not stereoselective.
Co-reporter:Carol A. Deakyne, Aaron K. Corum, Haunani M. Thomas, Joel F. Liebman
Journal of Fluorine Chemistry 2006 Volume 127(Issue 10) pp:1355-1367
Publication Date(Web):October 2006
DOI:10.1016/j.jfluchem.2006.07.015
In the current paper, we discuss our high level quantum chemical results for the structure and energetics of singlet (closed-shell) isomers corresponding to the stoichiometry of one boron, carbon, and fluorine apiece, and two hydrogens. While the ketene- and diazomethane-like H2CBF plausibly emerges as the most stable isomer, a variety of novel structural features emerge for the assembled energy minima. All of these species are compared as well as transition states that connect them. Comparison is also made with corresponding forms of the aforementioned ketene and diazomethane to which our species are isoelectronic, as well as with our earlier studied [B, C, F, H3]+ which may be recognized as the protonated counterparts of the species of direct interest in this study.This figure is a partial potential energy diagram for [B, C, F, H2] showing the interconversion pathways between four key isomers. Also included are the activation barriers in both directions, calculated as the difference in the zero-point energy corrected total energies of the transition structure and the relevant minimum.
Co-reporter:Yadu B. Tewari, Karen W. Phinney, Joel F. Liebman
The Journal of Chemical Thermodynamics 2006 Volume 38(Issue 4) pp:388-395
Publication Date(Web):April 2006
DOI:10.1016/j.jct.2005.06.005
The equilibrium constants for the ketoreductase-catalyzed reactions (cycloalkanone + 2-propanol = cycloalkanol + acetone) have been measured in n-hexane, n-pentane, and supercritical carbon dioxide SCCO2 (pressure = (8.0 to 12.0) MPa). The cycloalkanones included in this study were: cyclobutanone, cyclopentanone, cyclohexanone, cycloheptanone, and cyclooctanone. The equilibrium constants for the reactions involving cyclobutanone and cyclohexanone were measured in n-hexane over the range T = (288.35 to 308.05) K. The thermodynamic quantities at T = 298.15 K are: K = (0.763 ± 0.001); ΔrGm∘=(0.670±0.002)kJ·mol-1; ΔrHm∘=-(1.09±0.11)kJ·mol-1, and ΔrSm∘=-(5.9±0.4)J·K-1·mol-1 for the reaction involving cyclobutanone; and K = (15.7 ± 0.2); ΔrGm∘=-(6.82±0.02)kJ·mol-1; ΔrHm∘=-(4.6±1.0)kJ·mol-1, and ΔrSm∘=(7.4±3.3)J·K-1·mol-1 for the reaction involving cyclohexanone, respectively. An inspection of the equilibrium constants for these reactions in n-hexane, n-pentane, and SCCO2 shows that solvent dependence is not significant. The equilibrium constants of cycloalkanones decrease with increasing value of the number of carbons, NC with the exception of cyclohexanone. The cyclohexanol, which adopts a nearly strainless, idealized tetrahedral conformation around each carbon, is thermodynamically favored and more stable compared to other cycloalkanol rings, and this is reflected in the significantly higher value of the equilibrium constant obtained for this reaction. Comparisons with results obtained by using two independent thermochemical routes are also made.
Co-reporter:Maja Ponikvar;Joel F. Liebman;H. Donald B. Jenkins
European Journal of Inorganic Chemistry 2004 Volume 2004(Issue 16) pp:
Publication Date(Web):7 JUN 2004
DOI:10.1002/ejic.200400150
Chemical analysis of Sb in coordination compounds requires quantitative reduction of SbV in the form of SbF6− (and its related fluoro-hydroxy species) to SbIII. This process, although thermodynamically favoured, appears to be kinetically hindered. The experimentally observed stabilisation of SbF6− towards reduction, as happens when the associated metal counterion is complexed by XeF2 (generally regarded as being an oxidizing agent), is also discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Co-reporter:Maja Ponikvar;Borka Sedej;Joel F. Liebman
European Journal of Inorganic Chemistry 2004 Volume 2004(Issue 6) pp:
Publication Date(Web):17 FEB 2004
DOI:10.1002/ejic.200300632
Results of elemental chemical analyses of the coordination compounds of the type LnFn(AsF6)3-n (Ln = Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) indicated unexpectedly low stability of the generally highly hydrolytically stable [AsF6]− ion. Experiments conducted on model compounds of the type NdFn(AsF6)3-n have shown that hydrolysis proceeded instantaneously during the reaction of the solid compound with water. The ligand substitution catalysis of the compounds is explained in terms of the distortion of the [AsF6]− octahedra earlier shown by vibrational spectroscopy. The study contrasts formally related reactions on the solid−solvent interface as opposed to those in homogeneous solution. A new look at some long studied and well-known inorganic species is offered. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
Co-reporter:Robert Vianello Dr. Dr.;Zvonimir B. Maksić Dr.
Chemistry - A European Journal 2004 Volume 10(Issue 22) pp:
Publication Date(Web):14 OCT 2004
DOI:10.1002/chem.200400337
An efficient but reasonably accurate B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) computational procedure showed that pentasubstituted cyclopentadienes such as (CN)5C5H, (NO2)5C5H, and (NC)5C5H containing strongly electron-withdrawing groups are neutral organic superacids of unprecedented strength. The boldface denotes the atom attached to the cyclopentadiene framework. All of them exhibit prototropic tautomerism by forming somewhat more stable structures with CNH, NO2H, and NCH exocyclic fragments, respectively. The acidity (ΔHacid) of these is lower, but only to a rather small extent. The ΔHacid enthalpies of these last three tautomers are estimated to be 271, 276, and 282 kcal mol−1, respectively. Hence, the most stable tautomers of (CN)5C5H and (NC)5C5H represent a legitimate target for synthetic chemists. On the other hand, (NO2)5C5H is less suitable for practical applications, because of its high energy density. The origin of the highly pronounced acidity of these compounds was analyzed by using the recently developed triadic formula. It is found that very high Koopmans' ionization energy (IE) of conjugate bases exerts a decisive influence on acidity. It follows as a corollary that the overwhelming effect leading to very high acidity is due to the properties of the final state. An alternative picture is offered by homodesmotic reactions, wherein the cyclic systems are compared with their linear counterparts. It is found that the acidity of cyclopentadiene (CP) is a consequence of aromatic stabilization in the CP− anion. The extreme acidity of pentacyanocyclopentadiene (CN)5C5H is due to aromatization of the five-membered ring and a strong anionic resonance effect in the resultant conjugate base. The neutral organic superacids predicted by the present calculations may help to bridge the gap between existing very strong acids and bases.
Primjenom B3LYP/6-311+G(d,p)//B3LYP/6-31G(d) metode pokazano je da organski spojevi poput pentasupstituiranih ciklopentadiena (CN)5C5H, (NO2)C5H i (NC)5C5H pokazuju izuzetno veliku kiselost usljed djelovanja jakih elektron-akceptorskih grupa. Važno je istaknuti da su najstabilniji oblici ovih spojeva prototropni tautomeri, koji posjeduju CNH, NO2H i NCH egzocikličke fragmente. Njihova kiselost je nešto manja od tautomera, koji posjeduju C(sp3) ugljikov atom. Unatoč tome, njihove entalpije ΔHacidsu 271, 276 i 282 kcal mol−1, što znači da se radi o rekordno jakim superkiselinama. Uzrok ovako visoke kiselosti supstituiranih ciklopentadiena analiziran je primjenom nedavno razvijene trihotomske formule. Ustanovljeno je da dominantan utjecaj ima Koopmansova ionizacijska energija (IE) konjugiranih baza nastalih deprotoniranjem. No znatan doprinos kiselosti daje i aromatizacija peteročlanog prstena i vrlo jaka anionska rezonancija u konjugiranim bazama. Možemo, dakle, zaključiti da su superkisela svojstva spomenutih supstituiranih ciklopentadiena posljedica karakteristika konačnog stanja. Sinteza ovih spojeva pridonijet će stvaranju zajedničke ljestvice superkiselina i superbaza.
Co-reporter:Joel F. Liebman, Carol A. Deakyne
Journal of Fluorine Chemistry 2003 Volume 121(Issue 1) pp:1-8
Publication Date(Web):1 May 2003
DOI:10.1016/S0022-1139(03)00009-5
This review is composed of six vignettes. They deal with respectively: the reaction of Xe and PtF6; the reaction of O2 and O3 with PtF6; salts of O+, the covalent OF, and noble gas-containing cations; synthesis, reactions and structure of [XeO2]+ en route to [XeF]+ salts; [Xe2]+, green and related species; neutral xenon oxides, nonmetal oxyanions, and a nonmetal fluoride “mid-valence” crisis. Interrelations and interactions are emphasized.Graphic
Co-reporter:Carol A Deakyne, Le Li, Joel F Liebman
International Journal of Mass Spectrometry 2003 Volume 227(Issue 3) pp:555-561
Publication Date(Web):July 2003
DOI:10.1016/S1387-3806(03)00098-8
There is a marked paucity of reliable energetics data for ions containing boron, carbon, fluorine and hydrogen. Even one of the conceptually most simple ions, [B, C, F, H3]+, is poorly understood because its sole measurement is part of a 40-year-old electron impact study on CH3BF2. Intuition suggests this ion has the structure [CH3BF]+. What else could it be—it is isoelectronically related to the well-known CH3CN, [CH3CO]+ and [CH3N2]+? What about [BH3CF]+, isoelectronic to the well-known BH3CO and [BH3CN]−? We use high level quantum chemical calculations in the current study to disclose 10 minima: [CH3BF]+ is the most stable and [BH3CF]+ is not even a minimum. Derived quantitative energy differences and qualitative reasoning are used for the understanding of the various isomeric forms of the [B, C, F, H3]+ ion, and by inference and extension in future studies, other ions containing boron, carbon and fluorine.
Co-reporter:María Victoria Roux, Manuel Temprado, Juan Zenón Dávalos, Pilar Jiménez, Ramachandra S. Hosmane and Joel F. Liebman
Physical Chemistry Chemical Physics 2002 vol. 4(Issue 15) pp:3611-3613
Publication Date(Web):20 Jun 2002
DOI:10.1039/B202033E
Methyl benzoate is a particularly simple and important organic compound. We are thus not prepared for the “discovery” that there are three relatively recent literature determinations of its enthalpy of formation that span a 15 kJ mol−1 range. The current study provides yet another, more reliable, measurement of the energy of combustion of this species, −3956.7±3.1 kJ mol−1. Joined with one obtained from the literature a weighted average value for the enthalpy of formation in liquid phase for methyl benzoate can be given as ΔfHm°(l)=−332.8±4.0 kJ mol−1 Combined with a literature suggested value for the enthalpy of vaporization we obtain the standard molar enthalpy of formation of methyl benzoate in gaseous state, ΔfHm°(g)=−276.1±4.0
kJ mol−1. Confident of this new value, we reconcile a disconcerting disparity in the energetics of other methyl benzenecarboxylates discussed in the recent literature.
Co-reporter:Maria Victoria Roux, Rafael Notario, Diana N. Zeiger, Joel F. Liebman
Journal of Fluorine Chemistry 2001 Volume 112(Issue 1) pp:91-94
Publication Date(Web):28 November 2001
DOI:10.1016/S0022-1139(01)00491-2
It is well-established that the strain energy of cycloalkanes is affected by fluorination. While the strain energies of cyclopropane and cyclobutane are very nearly equal, perfluorination markedly increases the strain energy of the former and correspondingly decreases the latter. The numerical value for the strain energy of a given molecule is model-dependent. We discuss the strain energies of fluorinated cycloalkanes in terms of the “ultradiagonal” approach, a method earlier found useful for the understanding of fluorinated cyclopropanes and other species containing three-membered rings.
.jpg)
![Cyclopenta[cd]pentalene,2a,3,4,4a,5,6,6a,6b-octahydro-](http://img.cochemist.com/ccimg/57600/57595-39-8.png)
![Cyclopenta[cd]pentalene,2a,3,4,4a,5,6,6a,6b-octahydro-](http://img.cochemist.com/ccimg/57600/57595-39-8_b.png)
![[(methoxysulfanyl)oxy]methane](http://img.cochemist.com/ccimg/28800/28752-20-7.png)
![[(methoxysulfanyl)oxy]methane](http://img.cochemist.com/ccimg/28800/28752-20-7_b.png)
![2-{[(4-METHOXY-3,5-DIMETHYL-2-PYRIDINYL)METHYL]SULFINYL}-5-[(<SUP>2</SUP>H<SUB>3</SUB>)METHYLOXY]-1H-BENZIMIDAZOLE](http://img.cochemist.com/ccimg/7800/7791-21-1.png)
![2-{[(4-METHOXY-3,5-DIMETHYL-2-PYRIDINYL)METHYL]SULFINYL}-5-[(<SUP>2</SUP>H<SUB>3</SUB>)METHYLOXY]-1H-BENZIMIDAZOLE](http://img.cochemist.com/ccimg/7800/7791-21-1_b.png)
![TRICYCLO[8.2.2.2<SUP>4,7</SUP>]HEXADECA-1(12),4,6,10,13,15-HEXAENE-5,11-DIYLBIS[BIS(3,5-DIMETHYLPHENYL)PHOSPHINE]](http://img.cochemist.com/ccimg/7300/7289-53-4.png)
![TRICYCLO[8.2.2.2<SUP>4,7</SUP>]HEXADECA-1(12),4,6,10,13,15-HEXAENE-5,11-DIYLBIS[BIS(3,5-DIMETHYLPHENYL)PHOSPHINE]](http://img.cochemist.com/ccimg/7300/7289-53-4_b.png)
![tricyclo[1.1.0.0~2,4~]butane](http://img.cochemist.com/ccimg/200/157-39-1.png)
![tricyclo[1.1.0.0~2,4~]butane](http://img.cochemist.com/ccimg/200/157-39-1_b.png)
