The Vibrational Spectrum and Structure of Organic Crystals: Urea, Thiourea, Glycine

Citation

Waldron, Robert Douglas (1952) The Vibrational Spectrum and Structure of Organic Crystals: Urea, Thiourea, Glycine. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/YKFT-HQ71. https://resolver.caltech.edu/CaltechTHESIS:02292012-090540895

Abstract

Investigations of the infra-red spectra of single crystals of urea, thiourea, glycine, and deuterium derivatives with polarized radiation are presented. The polarization measurements are of value in identifying the normal vibrations.

For urea, evidence is presented that the molecular structure is entirely planar. Frequency assignments are made for 14 of the 18 fundamental vibrations tor urea and deutero-urea. A valence force calculation of the skeletal force constants is made. The isotope product rule is applied to the vibrations of 2 symmetry species.

For thiourea, the spectrum is closely related to that of urea. Frequency assignments of fundamental vibrations are made for 15 frequencies of thiourea and 12 frequencies of deutero-thiourea. A valence force calculation of the skeletal force constants is made. The isotope product rule is used to calculate 2 of the unobserved frequencies of deutero-thiourea. Evidence is given in support of a planar or nearly planar molecular structure.

The spectrum of glycine yields polarization data giving the orientation of the transition moment of individual vibrations. This is applied to the analysis of the observed frequencies. The polarizations of the absorption bands associated with stretching vibrations of the NH^+_3 group are compatible with restricted rotation of that group about the C-N bond. The relation between vibrational frequency and hydrogen bonding is discussed. The use of partially deuterated glycine permits the study of the effects of individual hydrogen bonds on the frequency and band shape of ND stretching vibrations.

Some features of the polarization technique are used to predict group orientations in the l-leucine crystal.

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