Band assignments methyl groups

The IR spectra of methyllithium exhibited two C—H bending vibrational modes at 1480 and 1427 cm . Their assignment was again substantiated by significant isotopic shifts to 1100 and 1043 cm in the deuterium compound (Table 1). Only one weak band was observed for ethyllithium in the C—H deformation region at 1450 cm . Moreover, a new sharp peak was detected at 1385 cm and ascribed to the C—H symmetrical bending mode of CH3. Its absence in the IR spectrum of methyllithium is a further indication that free methyl groups exist only in ethyllithium. 

The absorption of methyl groups occurs at 1375 cm.,"1 but this seems an improbable assignment here. Perhaps the band represents a coupling... 

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