The infrared spectra of methyl substituted aromatic hydrocarbon with aniline have been obtained in the 3400-1670 cm^-1 region. The many researches on the effects of hydrogen bonding on the vibrations of hydroxyl groups have provided information from which the environment of hydroxyl groups in molecules can be deduced. Factors influencing infrared absorption of aromatic aldehyde groups have not yet been so fully explored. This paper presents information obtained from an examination of these groups in Ccl₄ solution.