Observation of an Eclipsed C‐CH₃ Bond in a Tricyclic Orthoamide; Experimental and Theoretical Evidence for CH O Hydrogen Bonds

Abstract

The inversion of the rotational barrier of a methyl group can be accomplished by a suitable arrangement of water molecules, as shown by X-ray crystal structure investigations of the orthoamide 1. In the trihydrate, the methyl group adopts a nearly elipsed conformation, whereas in the anhydrous compound the normal staggered conformation is found. The H…O bond strengths of the C−H·O hydrogen bonds required for this inversion (ca. 1.8 kcal nol−1) were confirmed by quantum-chemical calculations only when correlation effects were taken into consideration.