Large structural effects in neutral and protonated species: a computational study

The B3LYP/6-31G(d) methodology was applied to the study of the diketone pen tacyclo[5.4.0.0(2) (,6).0(3,10).0(5,9)] undecane-8,11-dione (1), the hydroc arbon pentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecane (2) and the ketone pe ntacyclo[5.4.0.0(2,6).0(3,10).0(5, 9)]undecane-8-one (3). Also examined wer e the oxygen-protonated species 1H(+) and 3H(+). The diketone pentacyclo[5. 4.0.0(2,6).0(3,10).0(5,9)]undecane-4,8-dione (4) and the ketone pentacyclo[ 5.4. 0.0(2,6).0(3,10).0(5,9)]undecane-4-one (5) and their protonated forms were used for comparison purposes. This information was used to construct s everal isodesmic reactions, allowing the quantitative estimate of the influ ence of the carbonyl groups on the stability of the various species in the gas phase. These results were in excellent agreement with the experimental thermochemical and structural data available. Analyses by means of the natu ral bond orbital theory and simple electrostatic models were also performed . Copyright (C) 2001 John Wiley & Sons, Ltd.