Studies of steric hindrance and intramolecular interactions in 3-vinylcoumarin and its fluorinated analogues

Density Functional Theory (DFT) has been applied to the study of intramolecular interactions in 3-vinylcoumarin and its analogues, containing respectively 1, 2 or 3 fluorine atoms in vinyl fragment. In calculations, rotational isomerism around the single C3-C11 bond was considered in order to find the most stable conformers. The optimum geometry was obtained for different conformations. The dependence of substitution position on geometrical parameters and Gibbs free energy has been estimated to establish how electronic interactions contribute to the bent geometry. Theoretical investigation in the gas phase has led to the conclusion, that fluorine can be involved in the intramolecular hydrogen bond formation in our model compounds. That results in a better overlap of side orbitals, planarity of the molecule and thermodynamic stability. (c) 2005 Elsevier B.V. All rights reserved.