Vibrational spectra and symmetry of 3,3,6,6-tetramethylcyclohexa-1,4-diene

The vibrational spectra of 3,3,6,6‐tetramethylcyclohexa‐1,4‐diene as a vapour, a liquid, a crystalline solid and isolated in argon and nitrogen matrices at 13K have been recorded and interpreted in terms of a planar ring structure (D2h). The fundamental modes of vibration have been assigned with the aid of a normal coordinate calculation and by comparison with the spectra of cyclohexa‐1,4‐diene.