Studies of sterically hindered and overcrowded molecules

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Abstract
A comparative study of the proton magnetic resonance spectra of the mono-, di-, tri- and tetra-t-butyl and methyl substituted benzenes shows that a t-butyl group interacts with the ring as strongly as a methyl group. Low-field chemical shifts of ring protons (amounting to -0·50 p.p.m.) and t-butyl protons (amounting to -0·23 p.p.m.) ortho to a t-butyl group are attributed to intramolecular van der Waals forces. The possibility of severe ring puckering in the t-butylbenzenes is rejected since it is felt that this phenomenon should produce high-field shifts of the ring proton signals.