1H and 13C NMR Studies of Conformational Substituent Effect in 4- and 5-Monosubstituted Derivatives of Benzocycloheptene

Article abstract of DOI:10.1016/S0040-4020(01)91866-6

Values of -ΔG^o for the axial<*>equatorial conformational equilibrium of the chair form of 5-substituted (2-8) and 4-substituted (9-14) derivativesof benzocycloheptene were measured from their 1H and/or 13C NMR spectra recorded under conditions of slow exchange (T < 80 deg C).Strikingly different conformational substituent effects are noted in each series of compounds.The results are compared with equivalent parameters published for analogous six-membered cyclic derivatives and interpreted in terms of steric and electrostatic interactions.Substituent effects on 13C NMR chemical shifts were measured and are compared to those reported for the cyclohexane ring.