Carbon-13 chemical shifts and substituent effects in 4-substituted camphors, N-nitrocamphorimines, and diazocamphors

Abstract

Carbon-13 chemical shifts of a series of 4-substituted camphors (1)–(11) are reported, and are considered in relation to substituent effects and related systems. Electron-withdrawing substituents cause high-field shifts of the carbonyl carbon [C(2)] signal, whose shieldings correlate empirically with the linear free energy parameter, σ_I. In the derived nitroimines (13)–(l7), where no evidence is found for geometrical isomerism at the carbonnitrogen double bond, C(2) is shielded by ca. 30 p.p.m. with respect to the corresponding camphor. In compounds (2), (5). and (11) and norcamphor, deuteriation at C(3) brings about high-field isotope shifts at certain carbon atoms. Carbon-13 and nitrogen-15 chemical shifts of diazocamphors and 9-diazofluorene are reported and discussed.