The PMR spcctra of twelve pinene derivatives are reported, analysed and assigned. The proton couplings in the bridged cyclobutane group are compared with those of other strained cyclobutanes, and the relationship between 2 J~f~ and the C.CH,.C angle is shown to be anomalous in these systems, suggesting unusually small H.C.H. angles in cyclobutanes.The very large values of 4 J~~( e q -e q ) in buckled cyclobutanes are interpreted in terms of current M.O. theory and also given a simple geometric rationalisation based on the direct mechanism.The various couplings in the pinene skeleton are discussed in terms of present theories and minor conformational effects in these molecules. Substituent chemical shift (SCS) values for Me and OH groups around the pinene skeleton are obtained, and shown not to agree with calculations based on present theories of chemical shifts.

Nuclear magnetic resonance and chemical evidence shows that the product of lithium aluminium hydride reduction of verbenone is cis-verbenol, and that of lead tetra-acetate oxidation of a-pinene is trans-verbenol. The physical properties of both alcohols differ from those reported for the alcohols separated from the product of Meerwein-Po n ndorf-Verley reduction of verbeno ne.

The 220 MHz 'H spectra of isoverbanone, nopinone and verbanone are reported. The spectra of the first two are completely assigned but that of verbanone only partially. The coupling constants obtained provide information about the conformation of these molecules. The isoverbanone molecule is almost Y shaped, but that of nopinone is between a Y shape anda half-chair conformation with the six membered ring bent away from the gem dimethyl groups. These conformations are consistent with the known steric interactions in these molecules.

Methanolysis of the 2-pinanyl p-nitrobenzoates in the presence of base gives a mixture of products including both cis-and trans-methyl 2-pinanyl ethers from both esters. In contrast, other substitution products show a rigid retention of stereochemistry. It is suggested that each ester forms a delocalised ion, and that these ions can subsequently be interconverted. The results contrast with data reported from the study of the nopinol system, but both sets of results have been shown to be consistent with a mechanism of interconversion of ions in which two possible reaction paths exist, the direction of reaction being controlled by the substituent on C-2. Elimination products fit this general pattern except for a very high yield of a-pinene from the cis-ester, which may arise from elimination within an intimate ion pair, rather than from the ' free ' ion. The trans-ester, in contrast, gives an intimate ion pair which undergoes collapse rather than elimination. 6 N. A. Abraham and M.

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