Anab initio molecular orbital study of substituted carbonyl compounds
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Ab initio SCF calculations with a minimal STO-3G basis set have been performed to determine the equilibrium geometries of two series of carbonyl compounds, RCHO and R2 CO. For the mono-substituted compounds, R may be CH3, NH2, OH, F, CHO, and C2 H3. In the disubstituted compounds, R has been restricted to the isoelectronic saturated groups. The computed equilibrium geometries of these compounds are in satisfactory agreement with the experimentally-determined geometries, with an average difference of 0.021 Å between computed and experimental bond lengths, and 1.9 ° in corresponding bond angles. An analysis of the effect of the substituent on the electronic structure of the carbonyl group has also been made. The saturated groups are found to be electron-withdrawing groups relative to H, with the electron withdrawing ability increasing in the order CH3 <NH2 <OH <F. The unsaturated substituents CHO and C2H2 are also electron withdrawing relative to H, and comparable to CH3 in acetaldehyde. Vertical ionization potentials andn→π* transition energies have also been calculated for these molecules at their optimized geometries, experimental geometries, and geometries given by a standard model. The effect of changes in molecular geometry on these computed properties has been analyzed.
Key wordSubstituted carbonyls
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