S. N. Mathur

Microwave spectrum, conformation, and quadrupole coupling constants of cyclopentyl chloride

Abstract The microwave spectra of the normal and two isotopic species of cyclopentyl chloride have been observed and analyzed. For the normal isotopic species the rotational constants (in MHz) are A = 4547.77 ± 0.01, B = 2290.22 ± 0.01, and C = 2073.34 ± 0.01. From the rotational constant data, it has been shown that the stable molecular conformation is the bent axial form. Quadrupole coupling constants have been measured for the 35 Cl nucleus, the values being (in MHz) χ aa = −23.70 ± 0.10, χ bb = 32.33 ± 0.36, and χ cc = −8.63 ± 0.37. When transformed to the CCl bond axis system, the coupling constants confirm the axial structure. Extensive vibrational satellite structure, presumably arising from the pseudorotational ring mode with a fundamental frequency of 52 ± 5 cm −1 , has been observed and assigned. No spectral evidence has been observed for a second stable molecular conformer.

Microwave spectrum and substitution structure of methylene chloride

Abstract The microwave spectrum of methylene chloride has been reinvestigated in order to obtain a complete substitution ( r s ) structure of well-defined precision. Measurements on the 13 CH 2 Cl 2 species have yielded the following rigid-rotor rotational constants: A = 30746.20 ± 0.10 MHz, B = 3320.63 ± 0.11 MHz, and C = 3053.44 ± 0.10 MHz. These data, combined with revised values reported earlier for other isotopic species, yields the following r s structural parameters: CCl = 1.767 ± 0.002 A, CH = 1.085 ± 0.002 A, ∠HCH = 112.1 ± 0.2°, and ∠ClCCl = 112.2 ± 0.1°.

Microwave spectrum, structure, and dipole moment of bicyclo[3.1.0]hex-2-ene

Abstract The microwave spectra of the normal and four monosubstituted 13 C isotopic species of bicyclo[3.1.0]hex-2-ene have been observed and analyzed. For the normal species the rotational constants (in megahertz) are: Λ = 6306.121 ± 0.006, B = 4516.667 ± 0.004, C = 3208.823 ± 0.002. From the complete data set, a partial r s heavy-atom structure has been obtained as well as a complete effective structure. The r s distances are found to be C 1 C 5 = 1.521 ± 0.001 A, C 1 C 2 = 1.494 ± 0.010 A, C 5 C 6 = 1.482 ± 0.006 A, C 1 C 6 = 1.522 ± 0.007 A. The overall effective structure shows the five-membered ring to be only slightly nonplanar (by ca. 6°), and the three-membered ring to be rather sharply inclined with respect to the five-membered ring (dihedral angle C 1 C 5 C 6 -C 1 C 5 C 4 = 113.5°). Dipole moment measurements for the symmetryless molecule yielded values of | μ a | = 0.166 ± 0.009, | μ b | = 0.209 ± 0.015, | μ c | = 0.119 ± 0.001, | μ T | = 0.292 ± 0.012 D.

Microwave spectra of deuterated forms of bicyclo[2.1.0]pentane and the complete molecular structure

The microwave spectra of six deuterium‐labeled species of bicyclo[2.1.0]pentane have been observed and analyzed. These data, along with previously published results for the heavy atoms, permit the evaluation of a complete molecular structure for this polycyclic system. Some pertinent structural parameters include: R (C1H) =1.082±0.003 AAR (C2H, exo) =1.085±0.007 AAR (C2H,endo) =1.097±0.009 AAR (C5H,exo) =1.088±0.002 AAR (C5H, endo) =1.090±0.003 AA‖HC2H=109.4°±0.3 °, and ‖HC5H=116.7°±0.4°. In addition, all methylene groups have been found to be tilted in the exo direction by nearly three degrees.

Microwave spectrum and dipole moment of 1,1-dimethylcyclopropane; the polarity of the methyl group

Abstract The microwave spectrum of 1,1-dimethylcyclopropane has been observed and analyzed, yielding the following rotational constants: A = 6135.257 ± 0.016 MHz, B = 5203.342 ± 0.015 MHz, C = 3810.509 ± 0.019 MHz. Measurements of the Stark effect for this C 2V molecule led to an electric dipole moment of μ = 0.142 ± 0.001 D. International rotation splittings were absent in all observed transitions (up to J ⩽ 20), which implies a high barrier of the same magnitude as that in the monomethyl analog. Dipole moment data from the present and related studies have been utilized to obtain an understanding of the polarity of the methyl group.

Two‐dimensional oscillators with C4v potential functions

A quantum‐mechanical investigation of two‐dimensional oscillators having C4v potential functions has been performed. The symmetry properties of such systems have been elucidated, and the state symmetries have been correlated with C∞v and C2v cases. Numerical calculations are presented to illustrate the behavior of the energy levels as a function of the potential energy coupling term. The results show clearly how degeneracies arise and are broken as the coupling term varies between limiting cases. The C4v case that has been numerically treated shows both double‐minimum and fourfold tunnelling phenomena, and would be an appropriate zero‐order model for describing the amino wagging motions of a molecule such as hydrazine.