MAGNETIC SUSCEPTIBILITY ANISOTROPY, MOLECULAR QUADRUPOLE MOMENT, MOLECULAR G VALUES, AND SIGN OF ELECTRIC DIPOLE MOMENT IN METHYLACETYLENE

The high-field molecular Zeeman effect has been observed for CH3C=CH, CH3C=CD, and CD3=CH under high resolution. An analysis of the data gives the perpendicular molecular g values of g┴ = +0.00350 ± 0.00015 for CH3C=CH, g┴ = +0.00271 ± 0.00015 for CD3C=CH, and g┴= +0.00367 ± 0.00015 for CH3C=CD. The parallel molecular g value is g11 = 0.312 ± 0.002 for methylacetylene. The magnetic susceptibility anisotropy is found to be (x┴ — χ||) = (7-70 ± 0.14) × 10−6erg/(G2mole), and the molecular quadrupole moment in CH3C=CH is Q|| = (+4.82 ± 0.23) × 10−26 esu cm2. The sign of the electric dipole moment for methylacetylene is found to be +CH3G=CH−. The elements in paramagnetic susceptibility tensor are [formula-ommited] = 9.50 ± 0.03 and [formula-ommited] = 158.41 ± 0.04 in units of 10−6erg/(G2 mole). The anisotropy of electronic charge distribution is [formula-ommited] = (33.28 ± 0.05) × 10−16 cm2. Using an estimated bulk magnetic susceptibility, the total magnetic susceptibility tensor elements are determined, giving [formula-ommited] = —36.6 ± 2.1 in units of 10−6 erg/(G2 mole). The second moments of electronic charge distribution are 〈0|σiai2|0〉 = (38.72 ± 0.30) × 10−16 cm2 and 〈0|σibi2|0〉 = (5.44 ± 0.25) × 10−16 cm2. The a axis is the symmetry axis of the molecule. The D-C bond deuterium nuclear quadrupole coupling constant is determined for CD3C=CH to be χD(C-D bond) = +(176 ± 15) kHz. The results are discussed and comparisons are made with other similar molecules. © 1969, American Chemical Society. All rights reserved.