0 Determined on a Varían A-60 spectrometer in CC14; values are given in ppm relative to (CH3) 4Si as internal standard; letters in parentheses denote singlet (s), doublet (d), triplet (t), broad (br), coupling constant(J); numbers in parentheses de-note number of protons determined by integration of areas. 6 Peak disappears on addition ofD20. three methyl groups which are either a to an oxygen or are olefinic. This observation places the double bond in the 1 or 1 (6) position. It is of interest to compare the chemical shifts of the C-2 and C-3 protons in tetra-hydrocannabinol (I) and in cannabidiol6 (III). The olefinic proton in I (6.35) is unshielded as compared to that in III (5.59), while the reverse relationship exists as regards the C-3 protons (I, 3.14; III, 3.85). This can be readily understood by examination of molecular models of these two compounds. In cannabidiol, the aromatic ring, which can rotate freely, is most probably in the same plane as the C-3 hydrogen, which is there-fore unshielded. 7 In tetrahydrocannabinol the addi-tional ring tilts the aromatic ring, so that the latter is now in (or nearly in) the same plane as the olefinic proton, which is therefore unshielded. Such an effect is possible only if the double bond occupies the 1 position and the protons on the two asymmetric carbons are irons, ie, if tetrahydrocannabinol possesses structure I. This structural determination is supported by a partial synthesis. A solution of cannabidiol (III) in absolute ethanol containing 0.05% hydrochloric acid on boiling for 2 hr. gives a mixture of the starting material and I. It can be assumed that these rather mild conditions cause no isomerization of the asymmetric centers or of the double bond.

Tetrahydrocannabinol (I) shows strong activity in the ataxia test8 in dogs. A full report will be sub-mitted elsewhere by Dr. H. Edery. Acknowledgments.—We are indebted to Prof. F. Sondheimer for his kind interest and encouragement, to Dr. Y. Shvo for the nmr spectra, to Dr. H. Edery of the Israel Institute for Biological Research for the