Conformations of Bark Beetle Pheromones: The Importance of the Medium.

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Abstract
The conformational composition of ipsenol (1) and ipsdienol (2) has been investigated by 1H NMR and IR spectroscopy of solutions in CCl4 CFCl3 and MeOH. The relative energies of the stable conformations have been estimated by molecular mechanics calculations (MMPMI). In CCl4 and CFCl3 (to mimic the gas phase) the dominant conformations are those with an anti conformation of the carbon-carbon chain. For both compounds, the hydroxy group hydrogen is partly hydrogen bonded to the butadiene fragment of the molecules. In methanol, a conformation with a gauche rotamer around the C3-C5 bond is important in addition to the anti conformation. The conformational change takes place in a region of the molecule which has been shown to be important for the effect of the pheromone.