The transferability of the carbonyl group in aldehydes and ketones

The atomic and bond properties of the carbonyl group of a series of 42 aldehydes and ketones were calculated in order to analyze the transferability of this group. This was done by using the theory of atoms in molecules (AIM) on 6- 31++G**/ 6-31G* wave functions. We found that the magnitudes rho(r(c)), mu(O), mu(C), v(C), and lambda(3) differ between aldehydes and ketones, and can be said to be transferable within each of these series, with the exception of the formaldehyde molecule, which behaves in a specific way. We considered N(O), N(C), r1(O), r1(C), v(O), R, r, epsilon, and H(r(c)) as transferable dividing them into three groups: Aldehydes, methylketones, and ketones of greater length; we omitted formaldehyde, acetaldehyde, and acetone molecules, which behave in a specific way. Both the total and potential energies, either absolute or by unit of population of the C and O atoms, together with their summation, varied in accordance with molecule size and, therefore, cannot be considered transferable properties of the carbonyl group in any group of compounds. However, the molecular energies of the compounds studied can be reproduced extremely accurately by means of a group contribution model which distinguishes the classic fragments: H aldehyde, C=O, CH2, and CH3. The AIM study proves that this reproduction stems from the complementary variation which the values of the energies of the different fragments undergo throughout the series of compounds. At the level of accuracy with which we determined the maximum surface of the oxygen atom, none of the integrated properties are affected by the value of L(Omega). However, for the carbon atom the population and the first moment depend linearly on L(Omega) within each of the established groups, which prevents the values obtained for the above properties from being used directly in the analysis of transferability or evolutions of properties. The relationships between the concrete property and L(Omega), however, were found useful for both studies. (C) 1999 American Institute of Physics. [S0021-9606(99)30714-5].