13C Nuclear Magnetic Resonance Studies. 32. The 13C Spectra of Several Norbornyl Derivatives

The 13C n.m.r. spectra of several norbornyl derivatives have been recorded to examine the variation of 13C shieldings with molecular geometry. Since it is well established that nonbonded interactions between vicinal carbon nuclei lead to pronounced upfield shifts, the so-called γ effects, series of methyl-substituted norbornanes, norbornenes, norbornan-2-ones (norcamphors), and norborn-5-en-2-ones were prepared as model systems having a variety of γ interactions between vicinal methyl groups. The observed shifts of these methyl carbons are considered in terms of the dihedral angle relating the vicinal nuclei. The use of specific deuteration for unequivocal signal assignments of carbons geminal and vicinal to the site of deuteration is illustrated.