Structure of the Methyl Halides

Abstract

Microwave spectroscopic measurements on the partially deuterated forms of CH3Cl, CH3Br, and CH3I allow a determination of the structural parameters which is less subject to zero-point vibration errors than other methods. In addition, examination of all measured isotopic species reveals that the C—D distance is shorter than C–H by 0.009A, and the D—C—D angle greater than that for H–C–H by about 12 minutes. Best values of structural parameters for the species containing the light isotope of hydrogen only are C–Cl distance 1.781, C–Br 1.939, C–I 2.139, C–H 1.11 (same for all halides), H–C–H angle 110°31′ for CH3Cl, 111°14′ for CH3Br, and 111°25′ for CH3I. Deuteration not only gives a change in the C–H bond but also a well-correlated change in the quadrupole coupling constant of the halogen.

Experimental Molecular Structure

“…For 12, however, he found an anomalous electron scattering at a certain applied voltage, which should be taken account of in the interpretation of the data obtained (1). For CHaCi (17, 103) and CHaCN (37,47) the results of the electron diffrac tion measurements are in good agreement with those of the microwave in vestigations. The microwave measurement of CFsCI was not sufficiently complete for the determination of the molecular structure, but yielded moments of inertia in agreement with the electron diffraction data recently obtained by Bartell & Brockway (17).…”

The Rotational Zeeman Effect of Methyl-and Silylbromide

“…For SiH3Br the present study has shown, that the corresponding g-factor associated with the rotation of a silyl group has about the same absolute value but the opposite sign: <7 (SiHr) = -0. 32. Further examples are silane, where a gr-factor of <7(SiH ) = -0.27 was observed [18], and H3C-SiH3, where the contributions from the methyl-and silylgroups nearly cancel to give a very small g\\ of (/i; (H3csiH3) -±0.018 [19].…”

“…The geometries of the nuclear frames are taken from Refs. [31] and [32]. The bulk magnetic susceptibilities are calculated from the Pascal constants [33], with an assumed uncertainty of ± 5% for CH3Br and -because of the special bonding situation -± 10% for SiH3Br.…”

C-H and C-D interbond coupling in CHD2Cl

“…Previous work on CHD2C1 has included measurements of the microwave [11] and infrared spectra [12]. In this paper we present FTIR spectra of the fundamental and low-energy overtones of vapour-phase CHD2CI, and laser photoacoustic spectra of the Vca = 5 and 6 regions.…”