Two rotationally restricted tetrahydrocannabinol (THC) ehters were synthesized to test the concept that the psychopharmacological activity of cannabinoids derives, in part, from the orientation of the lone pairs of electrons of the phenolic hydroxyl oxygen. These compounds, O,2-propano-Δ 8 -THC (3) and O,10-methano-Δ 9 -THC (12), lock the orientation of the lone pairs of electrons toward and away from the cyclohexene ring, respectively, by restricting bond rotation through the formation of cyclic ethers