Ring vibrations and hydrogen deformations

The remaining characteristic region is that between 900 cm and 700 cm in which CH deformations occur. It has been shown in the 

2 3- and 2 4-Dimethylquinolines contain four free hydrogen atoms in the carbocyclic ring and only one in the heterocyclic ring. These show their strongest bands in this region at 755 cm and 758 cm (corresponding to or /zo-substitution), respectively. They 

The apparent ease with which the quinoline derivatives comply with these correlations is surprising. However, it should be remembered that, as in the case of the aromatic compounds, substitution by strongly polar groupinp will materially alter these CH frequencies. 

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