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Understanding the conformational, electronic and vibrational properties of Tetrahydrocannabinol (THC) and Cannabidiol (CBD). Pharmacophoric similarities and differences

(-)-trans-Δ9- tetrahydrocannabinol (THC) and (-)- cannabidiol (CBD) are natural cannabinoids found in cannabis plant which interact with cannabinoid receptors in human body. THC is primary psychoactive compound while CBD is non- psychotropic constituent, i.e. they have different receptor activity, function, and physiological effects. These dramatic differences in their behavior are derived from not so dramatic differences in their structures. Calculations of the structures and infrared and Raman spectra of all THC and CBD conformers were performed by means of density functional theory (DFT) at the B3LYP-D3BJ/6-31+G(d, p) level. Conformational flexibility due to the presence of alkyl (pentyl) side chain was thoroughly investigated and shown to be weakly dependent on the molecular frame . The result of the QSAR analysis by Keimowitz et al. J. Med. Chem. 43 (2000) 59–70 that for optimum affinity and potency the side chain must have conformational flexibility to fold over and thus come with its end methyl group close to the phenolic ring was examined with respect to the energies needed for such transformation. Assignments of the observed vibrational spectra reported in the literature were made by attempting to have a strong calculated band assigned to the strong observed band lying in the same narrow wavenumber interval. Evidences for intra- and intermolecular hydrogen bonding in CBD based on experimental and calculated data are given.

(-)-trans-Δ9- tetrahydrocannabinol ; (-)-cannabidiol ; Vibrational assignment ; Molecular conformation ; Hydrogen bonding

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