Vibrations of the y CH Modes

The spectra of substituted thiazole derivatives, especially the methyl derivatives, can be used to determine harmonic and combination bands of the T(ch) modes 27(c.,h T(c.hi + T C5H). nd 7(C2hi + 

It should be noted that several authors have assigned the band at 1616 cm to a vibration of the thiazole ring (128-131, 134). 

The vibrations of the thiazole ring have been assigned in the case of thiazole, using the appellations Wj to Wy for the in-plane vibrations and Fj and Fj for the out-of-plane vibrations (135). For the substituted derivatives, they are classified in series numbered I to X (see Table III-10) (99). 

It can be seen that of the series numbered I to VIII, five (I, II, III, IV, VII) are relatively constant in position, and because of the similarity of their frequencies they seem to correspond to the cu, oi2, 3, 0)4, and wy modes of thiazole. The frequencies classified as V and VI are variable, and it can be noted that  

It is possible that for the methyl derivatives of thiazole the variable frequencies of the series V and VI correspond to the modes resulting from a coupling of the V(c-ch,) vibration with the vibration in the case of 2- or 5-substituted derivatives and with the vibration in the case of 4-substituted derivatives (99). 

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