The vibrational spectrum of n-butylsilane is described. Complete assignments of fundamentals are made for the anti–anti (aa) conformer of Cs symmetry. The relative stabilities of the five different conformers are calculated, and the (aa) conformer emerges as the conformer of lowest relative energy, and thus the most abundant, entirely dominating the infrared and Raman spectra as confirmed by the spectra of the annealed crystal. The dipole moments of all the conformers are calculated to lie between 0.88 and 1 Debye, similar to the dipole moments of the conformers of n-butylgermane.Microwave measurements of this molecule seeded in a molecular jet were made using Fourier-transform microwave spectroscopy and confirmed the presence of the aa conformer, in addition to the anti–gauche (ag) and gauche–anti (ag) conformers. Measurement of rotational spectra for all four 13C-substituted isotopologues as well as the 29Si and 30Si species for the aa conformer allowed a heavy atom structure determination for this conformer.Highlights► Five possible conformers for n-butylsilane. ► Microwave spectra for aa conformer of n-butylsilane. ► The dipole moments of all the conformers are calculated to lie between 0.88 and 1 Debye. ► Rotational spectra of isotopologues of the aa conformer allowed a heavy atom structure determination.

The mid and far infrared and the Raman spectrum of 1,2-dibromopropane is reported in solid, liquid and gas. Several bands reported by earlier workers are not present in the spectrum of the purified material. Ab initio calculations of optimized geometry, energy, dipole moment, molar volume, vibrational spectrum and normal coordinate calculation were performed using the density functional B3LYP/6-311++g(3df,2pd), and the results used to assist a complete assignment of the 81 fundamental modes of vibrations of the three conformers of 1,2-dibromopropane. Relative energies found conformer A the lowest with G and G′ at 815.6 and 871.4 cm−1 higher. The temperature dependence of the Raman spectrum of the liquid was investigated in the CCC bending region and the relative energies determined. It was found that the G′ and G conformers lie 236 ± 11 and 327 ±11 cm−1, respectively above the A conformer, leading to the room temperature composition of the liquid as A, 65 ± 1; G′, 21 ± 1; G, 14 ± 1%. It is apparent that the calculated highest energy conformer G′ is stabilized more than the G conformer in the liquid. The G′ conformer has the lowest molar volume effectively changing the interaction distance between conformers in the liquid, and enhancing the effect of its dipole moment.

The infrared and Raman spectrum of 1,4-dichlorobutane is reported in solid, liquid and gas. Ab initio calculations for the nine stable or metastable conformers of 1,4-dichlorobutane are reported for Moller–Ploessett second order electron correlation and B3LYP density functionals with a variety of basis sets, using approximations as high as 6–311 + g(2d, 2p). Normal coordinate calculations were conducted for the nine conformers and the results used to provide assignments for some of the observed infrared and Raman bands. An attempt to use the assignments together with the ab initio intensities or Raman activities to investigate the composition of the liquid at room temperature proved modestly successful, and suggested that the populations are altered from those expected in the gas phase by interactions of the permanent electric dipole moments with the dipolar plasma in which the conformers are immersed in the liquid. A substantial disagreement between the Moeller–Ploessett and density functional results is reported, and the calculation of intensities and activities is insufficiently accurate to allow detailed interpretation of the spectrum of the room temperature liquid. A complete assignment of fundamentals is given for the conformer of Ci symmetry, and one Raman and one infrared band is identified with the C2h conformer. All the other infrared and Raman bands in the liquid or the gas are composites of several contributors.