Effects of modification of molecular structure on Raman spectral depolarization ratios: Aqueous betaine (CH₃)₃NCH₂CO₂·29D₂ O versus (CH₃)₄NBr·29D₂O

Replacement of a CH in (CH₃)₄N⁺ by a CO₂^- group raises ρ from 0.012 to 0.034 for symmetric N-C stretching and from ca. 0.026 to 0.031 for all-in-phase methyl C-H stretching. ρ for antisymmetric C-H stretching and CH₃ bending remains in the 0.73-0.75 range. No significant effect on ρ attributable to the failure of solvation sheath symmetry to match the symmetry of the solute molecule is seen either near ρ = 0 or near p = 3/4. The drastic change in charge distribution on going from cation to zwitterion, too, does not cause a major change near ρ=0. Corroborative evidence of weakness of interaction between most surrounding D₂O molecules and the Me₃N⁺ portion of the zwitterion, derived from the O-D stretching region of the Raman spectrum, and implying the absence of symmetry in the solvation sheath, is discussed in Appendix A.