Conformational analysis and structural stability of 3-fluoropropanals

The conformational stability and structure of 3-fluoro-, 3,3-difluoro- and 3,3,3-trifluoropropanal were investigated by ab initio calculations with the 3-21G, 3-21G^* and 6-31G^* basis sets. The calculated O...F and O...H equilibrium separations indicate possible dipolar interactions that would stabilize the molecules in the conformers with minimum oxygen-fluorine and maximum oxygen-hydrogen interactions. For 3-fluoropropanal, the trans-cis conformer is predicted by the 3-21G and 6-31G basis sets to be the most stable, while for 3,3-difluoropropanal, the gauche-cis conformer is predicted to be the most stable. 3,3,3-Trifluoropropanal is predicted by both basis sets to exist as a mixture of more than one conformation with a very small energy difference between the gauche, trans and cis conformers.