13C Chemical shifts and 13C15N coupling constants of some 15N-labelled bridgehead nitro compounds

Measurement of the 13C NMR spectra of the bridgehead nitro compounds 1a–5a has been performed. It is found that one‐bond 13C15N coupling is not necessarily a reflection of the degree of s character of the bridgehead carbon exocyclic bonding orbital. Although the magnitude of vicinal coupling to the bridgehead carbon increases, in accordance with the number of three‐bond pathways available for transmission of spin information, coupling is actually reduced by opposing contributions from through‐space intramolecular orbital interactions.