s-Trideuterobenzene and the Structure of Benzene

Abstract

THE first and probably largest single step in the solution of the spectroscopic problem of the structure and vibrations of benzene was taken when, by comparison of the Raman and infra-red spectra of C₆H₆ and C₆D₆, the eleven active fundamental frequencies were identified, and shown to have isotope shifts agreeing with an application of Teller's theorem to the D_6h model¹. It remained to determine the nine inactive frequencies, and secure the confirmation they should yield. For this purpose the plan outlined was to remove symmetry piecemeal by oriented deuteration in the sequence 1: 3: 5-C₆H₃D₃ (no centre), ]: 4-C₆H₄D₂ (no 3-fold axis), C₆H₅D (no centre, no 3-fold axis), thus allowing previously inactive frequencies to become active a few at a time.