AM1 calculation of hydration to aldehyde group in nitro‐substituted benzaldehydes

Hydration to the aldehyde group in nitro‐substituted benzaldehydes was studied theoretically by using an AM1 method. The calculated values of activation energy and heat of reaction showed good correlations with the experimental values of rate constants and equilibrium constants, respectively. To examine the hydration mechanism, localized molecular orbitals were calculated. Furthermore, expression of the molecular orbitals of supermolecular complexes in terms of occupied and vacant orbitals of the component molecules elucidated that the interaction between the lonepair orbital of water and the antibonding CO π‐orbital of aldehyde was important. 2,6‐DNBAl was concluded to be less reactive toward water than was 2.4‐DNBAl. This is consistent with the experimental result that the mutagenic activity of 2,4‐DNBAl depends not only on the reduction of the nitro group by a bacterial enzyme but also on the acetyl conjugation, but that in the case of 2,6‐DNBAl the mutagenic activity is manifested through the reduction by a bacterial enzyme. © 1993 John Wiley & Sons, Inc.