The intensity ratio of the methyl symmetric deformation mode (ca. 1375 cm−1) and a band at ca. 1440 cm−1 can be employed empirically to determine the presence of methyl groups directly attached to ethylenic carbon atoms. Spectra of approximately 70 di- and trisubstituted acyclic and cyclic compounds containing ethylene methyls were examined. A good correlation was obtained between the number of methyl groups and the intensity ratios.
