Conformations and Restricted Rotation about Amide C–N Bonds of 2,2-Dichloro-1′-formyl-3′,4′-dihydrospiro[cyclopropane-1,2′(1′H)-quinoline] and Related Compounds

Abstract

Abstract Conformational preference and rotational barriers of 1′,1′,2,2-tetrachloro-3′-formyl-1′a,7′b-dihydrospiro[cyclopropane-1,2′(3′H)-cyclopropa[c]quinolines] (1) and related N-formyl heterocyclic compounds were determined by 1H- and 13C-NMR spectroscopy. The sp-conformer is usually more preferable in 1 and their rotational barriers about amide C–N bond are within a relatively narrow range from 70.7 to 72.8 kJ mol−1. Infrared carbonyl absorptions of these compounds also support the preferred conformation from the NMR data. The results were discussed from the view point of N–C=O conjugation.