Carbon-13 Nuclear Magnetic Resonance Spectroscopy. Conformational Analysis of Methyl-Substituted Cycloheptanes, Cycloheptanols, and Cycloheptanones

The ^(13)C chemical shifts were determined of the carbons in 12 cycloheptanes, 21 cycloheptanols, and 8 cycloheptanones. In some cycloheptanols and cycloheptanones, the assignments have been obtained unambiguously by the synthesis of deuterated derivatives and the use of paramagnetic-shift reagents. Substituent effects for the different types of groups have been calculated. The most informative data about the cycloheptane conformations were provided by the relatively well understood y effects. The results are generally in good agreement with predictions based on the twist-chair form, which has been predicted by Hendrickson to be the most stable conformation. spectra. This fact was used to assign the resonances found for cis-trans mixtures of methyl-substituted cycloheptanols to specific isomers.