Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 2005
Publication Date: June 22, 2005
Citation: Momany, F.A., Willett, J.L., Bosma, W. 2005. Calculations to determine the experimental conformation of a cyclic insect pheromone using a novel multi-faceted ab initio approach [abstract]. American Chemical Society. Paper No. 98. Technical Abstract: A new pheromone from Galerucella calmariensis L. has recently been identified and has the chemical formula: 12,13-dimethyl-5,14-dioxabicyclo[9.2.1]tetradeca-1(13),11-dien-4-one. The structure was determined by mass spectrometry, NMR, and UV spectroscopy. The ring is flexible, and the preferred conformation difficult to deduce from NMR data. A molecular mirror image symmetry exists of the same energy as the original structure. The DFT(GIAO) calculated isotropic 1H and 13C chemical shifts for different conformations of low energy were compared with experiment. Two conformations of low energy were found within less than 0.5kcal/mol of each other, with small rms deviations from observed chemical shift values. Transition state barriers between energy minima were obtained using an eigenvalue following routine and new minimum energy conformations obtained by energy optimization from the transition states. Dihedral angle driving methods were used to examine how driving individual dihedral angles through mirror image values changes the low energy conformations. Quantum dynamics was carried out at the 4-31G* level of theory and many transitions to other conformations were observed.