Co-reporter:Frank Weinhold
The Journal of Organic Chemistry December 1, 2017 Volume 82(Issue 23) pp:12238-12238
Publication Date(Web):October 9, 2017
DOI:10.1021/acs.joc.7b02089
We employ ab initio and density functional methods to investigate the equilibrium structure and vibrational frequencies of extended cumulene monoketones [CH2═(C═)mO] and diketones [O═(C═)mO], in order to elucidate the electronic origin of the curious “kinked’” spine geometries that are common in such species. The dominant role of symmetry-breaking nO(π)-σ*CC interactions between the p-type lone pair of the terminal oxygen and adjacent unfilled CC antibonding orbital is demonstrated by NBO second-order delocalization energies, Fock matrix deletions, and natural resonance theory (NRT) descriptors, showing the general connection between cumulene kinking and CC bond-breaking reactions that split off CO. Our results provide simple rationalizations for (i) pronounced even/odd alternation patterns in the magnitude or direction of kinking, (ii) the nonexistence of O = C═C═O, (iii) the clear preference for trans-like over cis-like kinks, and (iv) the extreme sensitivity of kinking with respect to weak perturbations, such as cage or solvent effects, remote chemical substituents, improved treatments of electron correlation, and the like.
Co-reporter: Frank Weinhold
Angewandte Chemie International Edition 2017 Volume 56(Issue 46) pp:14577-14581
Publication Date(Web):2017/11/13
DOI:10.1002/anie.201708691
AbstractStandard quantum chemical methods have been employed to describe a variety of kinetically stable polyionic molecular species that are trapped in appreciable potential wells by chemical bonding forces, despite powerful electrostatic opposition that challenges conventional chemical detection and characterization. The studied species are covalent or dative analogs of “anti-electrostatic” hydrogen-bonded (AEHB) species, all illustrating how short-range quantum covalency can overcome the powerful “shielding” opposition of long-range electrostatic forces to form highly charged molecular species, analogous to known neutral or singly ionic counterparts. Computational predictions of representative structural, spectroscopic, and NBO-based electronic signatures of multiply charged analogs of common neutral species (CH3CH3, CO2, FeCO) are provided to suggest the unique material properties characteristic of this shielded domain of polyionic chemical phenomena.
Co-reporter:Guiqiu Zhang, Hong Li, Frank Weinhold and Dezhan Chen
Physical Chemistry Chemical Physics 2016 vol. 18(Issue 11) pp:8015-8026
Publication Date(Web):11 Feb 2016
DOI:10.1039/C5CP07965A
Noble-gas hydrides HNgY are frequently described as a single ionic form (H–Ng)+Y−. We apply natural bond orbital (NBO) and natural resonance theory (NRT) analyses to a series of noble-gas hydrides HNgY (Ng = He, Ne, Ar, Kr, Xe, Rn; Y = F, Cl, Br, I) to gain quantitative insight into the resonance bonding of these hypervalent molecules. We find that each of the studied species should be better represented as a resonance hybrid of three leading resonance structures, namely, H–Ng+ −:Y (I), H:− +Ng–Y (II), and H^Y (III), in which the “ω-bonded” structures I and II arise from the complementary donor–acceptor interactions nY → σ*HNg and nH → σ*NgY, while the “long-bond” (-type) structure III arises from the nNg → *HY/HY interaction. The bonding for all of the studied molecules can be well described in terms of the continuously variable resonance weightings of 3c/4e ω-bonding and -type long-bonding motifs. Furthermore, we find that the calculated bond orders satisfy a generalized form of “conservation of bond order” that incorporates both ω-bonding and long-bonding contributions [viz., (bHNg + bNgY) + bHY = bω-bonding + blong-bonding = 1]. Such “conservation” throughout the title series implies a competitive relationship between ω-bonding and -type long-bonding, whose variations are found to depend in a chemically reasonable manner on the electronegativity of Y and the outer valence-shell character of the central Ng atom. The calculated bond orders are also found to exhibit chemically reasonable correlations with bond lengths, vibrational frequencies, and bond dissociation energies, in accord with Badger's rule and related empirical relationships. Overall, the results provide electronic principles and chemical insight that may prove useful in the rational design of noble-gas hydrides of technological interest.
Co-reporter:Anne Knorr;Peter Stange;Dr. Koichi Fumino;Dr. Frank Weinhold;Dr. Ralf Ludwig
ChemPhysChem 2016 Volume 17( Issue 4) pp:458-462
Publication Date(Web):
DOI:10.1002/cphc.201501134
Abstract
Direct spectroscopic evidence for hydrogen-bonded clusters of like-charged ions is reported for ionic liquids. The measured infrared O−H vibrational bands of the hydroxyethyl groups in the cations can be assigned to the dispersion-corrected DFT calculated frequencies of linear and cyclic clusters. Compensating the like-charge Coulomb repulsion, these cationic clusters can range up to cyclic tetramers resembling molecular clusters of water and alcohols. These ionic clusters are mainly present at low temperature and show strong cooperative effects in hydrogen bonding. DFT-D3 calculations of the pure multiply charged clusters suggest that the attractive hydrogen bonds can compete with repulsive Coulomb forces.
Co-reporter:Anne Knorr;Peter Stange;Dr. Koichi Fumino;Dr. Frank Weinhold;Dr. Ralf Ludwig
ChemPhysChem 2016 Volume 17( Issue 4) pp:
Publication Date(Web):
DOI:10.1002/cphc.201600096
Abstract
The front cover artwork is provided by the group of Prof. Ralf Ludwig at the University of Rostock in collaboration with Prof. Frank Weinhold at the University of Wisconsin Madison. The image shows the cyclic tetramer of hydrogen bonded cations in ionic liquids. The like-charge attraction is supported by strong cooperativity and weakly coordinating anions. Read the full text of the Review at 10.1002/cphc.201501134
Co-reporter:Anne Knorr;Peter Stange;Dr. Koichi Fumino;Dr. Frank Weinhold;Dr. Ralf Ludwig
ChemPhysChem 2016 Volume 17( Issue 4) pp:
Publication Date(Web):
DOI:10.1002/cphc.201600097
Co-reporter:A. D. Clauss, M. Ayoub, J. W. Moore, C. R. Landis and F. Weinhold
Chemistry Education Research and Practice 2015 vol. 16(Issue 3) pp:694-696
Publication Date(Web):28 Apr 2015
DOI:10.1039/C5RP00061K
We respond to recent comments (Hiberty et al., 2015) on our earlier article (Clauss et al., 2014) concerning “rabbit ears” depictions of lone pair orbitals in water and other species.
Co-reporter:Dr. F. Weinhold;Dr. Roger A. Klein
Angewandte Chemie International Edition 2015 Volume 54( Issue 9) pp:2600-2602
Publication Date(Web):
DOI:10.1002/anie.201500262
Co-reporter:Dr. F. Weinhold;Dr. Roger A. Klein
Angewandte Chemie 2015 Volume 127( Issue 9) pp:2636-2638
Publication Date(Web):
DOI:10.1002/ange.201500262
Co-reporter:Allen D. Clauss, Stephen F. Nelsen, Mohamed Ayoub, John W. Moore, Clark R. Landis and Frank Weinhold
Chemistry Education Research and Practice 2014 vol. 15(Issue 4) pp:417-434
Publication Date(Web):02 Jun 2014
DOI:10.1039/C4RP00057A
We describe the logical flaws, experimental contradictions, and unfortunate educational repercussions of common student misconceptions regarding the shapes and properties of lone pairs, inspired by overemphasis on “valence shell electron pair repulsion” (VSEPR) rationalizations in current freshman-level chemistry textbooks. VSEPR-style representations of orbital shape and size are shown to be fundamentally inconsistent with numerous lines of experimental and theoretical evidence, including quantum mechanical “symmetry” principles that are sometimes invoked in their defense. VSEPR-style conceptions thereby detract from more accurate introductory-level teaching of orbital hybridization and bonding principles, while also requiring wasteful “unlearning” as the student progresses to higher levels. We include specific suggestions for how VSEPR-style rationalizations of molecular structure can be replaced with more accurate conceptions of hybridization and its relationship to electronegativity and molecular geometry, in accordance both with Bent's rule and the consistent features of modern wavefunctions as exhibited by natural bond orbital (NBO) analysis.
Co-reporter:Frank Weinhold and Roger A. Klein
Chemistry Education Research and Practice 2014 vol. 15(Issue 3) pp:276-285
Publication Date(Web):14 Mar 2014
DOI:10.1039/C4RP00030G
We address the broader conceptual and pedagogical implications of recent recommendations of the International Union of Pure and Applied Chemistry (IUPAC) concerning the re-definition of hydrogen bonding, drawing upon the recommended IUPAC statistical methodology of mutually correlated experimental and theoretical descriptors to operationally address the title question. Both direct and statistical lines of evidence point to the essential resonance covalency of H-bonding interactions, rather than the statistically insignificant “dipole–dipole” character that is persistently advocated in current textbooks. The revised conception of H-bonding is both supported by modern quantum chemical technology and consistent with the pre-quantal insights of G. N. Lewis and other bonding pioneers. We offer specific suggestions for how relatively minor changes in the usual discussion of Lewis-structural and resonance concepts—supported by modern web-based computational modeling tools—can readily accommodate this fundamental change of perspective.
Co-reporter: Frank Weinhold;Dr. Roger A. Klein
Angewandte Chemie 2014 Volume 126( Issue 42) pp:11396-11399
Publication Date(Web):
DOI:10.1002/ange.201405812
Abstract
Ab initio and hybrid density functional techniques were employed to characterize a surprising new class of H-bonded complexes between ions of like charge. Representative H-bonded complexes of both anion–anion and cation–cation type exhibit appreciable kinetic stability and the characteristic theoretical, structural, and spectroscopic signatures of hydrogen bonding, despite the powerful opposition of Coulomb electrostatic forces. All such “anti-electrostatic” H-bond (AEHB) species confirm the dominance of resonance-type covalency (“charge transfer”) interactions over the inessential (secondary or opposing) “ionic” or “dipole–dipole” forces that are often presumed to be essential for numerical modeling or conceptual explanation of the H-bonding phenomenon.
Co-reporter: Frank Weinhold;Dr. Roger A. Klein
Angewandte Chemie International Edition 2014 Volume 53( Issue 42) pp:11214-11217
Publication Date(Web):
DOI:10.1002/anie.201405812
Abstract
Ab initio and hybrid density functional techniques were employed to characterize a surprising new class of H-bonded complexes between ions of like charge. Representative H-bonded complexes of both anion–anion and cation–cation type exhibit appreciable kinetic stability and the characteristic theoretical, structural, and spectroscopic signatures of hydrogen bonding, despite the powerful opposition of Coulomb electrostatic forces. All such “anti-electrostatic” H-bond (AEHB) species confirm the dominance of resonance-type covalency (“charge transfer”) interactions over the inessential (secondary or opposing) “ionic” or “dipole–dipole” forces that are often presumed to be essential for numerical modeling or conceptual explanation of the H-bonding phenomenon.
Co-reporter:H. E. Zimmerman and F. Weinhold
The Journal of Organic Chemistry 2013 Volume 78(Issue 5) pp:1844-1850
Publication Date(Web):August 22, 2012
DOI:10.1021/jo301620k
We show how the bond–bond polarizability index, as originally introduced by Coulson and Longuet–Higgins in the Hückel-theoretic context, can be generalized in the natural bond orbital (NBO) framework to ab initio molecular orbital and density functional theory levels. We demonstrate that such a “natural bond–bond polarizability” (NBBP) index provides a flexible and quantitative descriptor for a broad spectrum of delocalization effects ranging from strong π aromaticity to weak intra- and intermolecular hyperconjugative phenomena. Illustrative applications are presented for representative delocalization effects in saturated and unsaturated species, chemical reactions, and hydrogen-bonding interactions.
Co-reporter:Frank Weinhold Dr.
Angewandte Chemie 2003 Volume 115(Issue 35) pp:
Publication Date(Web):15 SEP 2003
DOI:10.1002/ange.200351777
Zwei Konzepte der qualitativen MO-Theorie geben widersprechende Erklärungen für die Torsionsbarriere im Ethan, aber nur eine hält einer gründlichen Begutachtung stand (siehe Energieniveau-Schemata). Es zeigt sich, dass Bickelhaupts und Baerends' Plädoyer für das neo-sterische Konzept der „Vier-Elektronen-Destabilisierung“ (rechts) genau so illusorisch ist wie seine Vorgänger.
Co-reporter:Frank Weinhold Dr.
Angewandte Chemie International Edition 2003 Volume 42(Issue 35) pp:
Publication Date(Web):15 SEP 2003
DOI:10.1002/anie.200351777
Two tenets of qualitative MO theory suggest contradictory explanations of ethane torsional barriers, but only one stands up to rigorous examination (see energy level diagrams). Bickelhaupt and Baerends' defense of the neo-steric “four-electron destabilization” concept (right) is shown to be as illusory as its predecessors.
Co-reporter:Guiqiu Zhang, Hong Li, Frank Weinhold and Dezhan Chen
Physical Chemistry Chemical Physics 2016 - vol. 18(Issue 11) pp:NaN8026-8026
Publication Date(Web):2016/02/11
DOI:10.1039/C5CP07965A
Noble-gas hydrides HNgY are frequently described as a single ionic form (H–Ng)+Y−. We apply natural bond orbital (NBO) and natural resonance theory (NRT) analyses to a series of noble-gas hydrides HNgY (Ng = He, Ne, Ar, Kr, Xe, Rn; Y = F, Cl, Br, I) to gain quantitative insight into the resonance bonding of these hypervalent molecules. We find that each of the studied species should be better represented as a resonance hybrid of three leading resonance structures, namely, H–Ng+ −:Y (I), H:− +Ng–Y (II), and H^Y (III), in which the “ω-bonded” structures I and II arise from the complementary donor–acceptor interactions nY → σ*HNg and nH → σ*NgY, while the “long-bond” (-type) structure III arises from the nNg → *HY/HY interaction. The bonding for all of the studied molecules can be well described in terms of the continuously variable resonance weightings of 3c/4e ω-bonding and -type long-bonding motifs. Furthermore, we find that the calculated bond orders satisfy a generalized form of “conservation of bond order” that incorporates both ω-bonding and long-bonding contributions [viz., (bHNg + bNgY) + bHY = bω-bonding + blong-bonding = 1]. Such “conservation” throughout the title series implies a competitive relationship between ω-bonding and -type long-bonding, whose variations are found to depend in a chemically reasonable manner on the electronegativity of Y and the outer valence-shell character of the central Ng atom. The calculated bond orders are also found to exhibit chemically reasonable correlations with bond lengths, vibrational frequencies, and bond dissociation energies, in accord with Badger's rule and related empirical relationships. Overall, the results provide electronic principles and chemical insight that may prove useful in the rational design of noble-gas hydrides of technological interest.
