A 1H and 13C NMR Conformational Study of Methyl-Substituted Isochromanes

Article abstract of DOI:10.1002/mrc.1260230915

The 1H and the noise-decoupled 13C NMR spectra of isochromane and 13 of its methyl-substituted derivatives were recorded and analysed.The collected data were used to assign the configurations and to determine the position of the conformational equilibria based on the vicinal 1H coupling constants of the aliphatic moiety of the ring-system.In some cases the substitution site-dependent conformational energies of the methyl substituents were also used to estimate the conformer ratios.The primary and some vicinal methyl substituent effects on the 13C chemical shifts of the oxane ring carbons were derived and compared with those of 1,3-dioxanes.Their usefulness in conformational analysis is demonstrated for 1-methylisochromane.