Numbering, Activity, and Nomenclature of the Vibrations

The planar structure of thiazole (159) implies for the molecule a Cj-type symmetry (Fig. 1-8) and means that all the 18 fundamental vibrations are active in infrared and in Raman spectroscopy. Table 1-22 lists the predictions made on the basis of this symmetry for thiazole. 

The distinction between in-plane A symmetry) and out-of-plane (A symmetry) vibrations resulted from the study of the polarization of the diffusion lines and of the rotational fine structure of the vibration-rotation bands in the infrared spectrum of thiazole vapor. 

The out-of-plane vibrations of thiazole correspond to C-type vibration-rotation bands and the in-plane vibrations to A, B, or (A + B) hybrid-type bands (Fig, 1-9). The Raman diffusion lines of weak intensity were assigned to A -type oscillations and the more intense and polarized lines to A vibration modes (Fig. I-IO and Table 1-23). 

From Table 1-24 it appears that A -type vibrations may, to a first approximation, decompose into six modes of vibration for CH bonds three for elongation v(CH), three for bending 6(CH), and seven for ring 

TABLE 1-22. NUMBERING AND ACTIVITY OF THIAZOLE RING VIBRATIONS (C SYMMETRY) 

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