Changing pictures of molecular faces and depths of potential acting on an electron in molecule for intramolecular proton transfer reactions of formic acid and malonaldehyde

Abstract

Proton transfer plays a critical role in many chemical and biological processes. MF theory is used to investigate intramolecular proton transfer reactions of formic acid and malonaldehyde. A MELD package with our in-house program is employed to calculate potential acting on an electron within a molecule (PAEM), molecular face (MF), molecular intrinsic characteristic contour (MICC) parameters, molecular face surface area (MFSA), as well as molecular face volume (MFV) of the two proton transfer reactions along the IRC routes. Vivid MF graphs are drawn. Then we found the following features: Firstly, the difference of frontier electron density (MICCED) distribution of formic acid is larger than malonaldehyde. Secondly, for formic acid, the trends of polarization and deformation of O atomic region are the same as another O, whereas opposite for malonaldehyde. Thirdly, the electron density uniformity of the formic acid reaction has minimum value at the transition state, whereas maximum with wave-like shape for malonaldehyde. Finally, the change tendencies of MFSA and MFV for formic acid are opposite to those for malonaldehyde. The uniformity of TS is a maximum from our PAEM method, Bader QTAIM and Gilli structure of views for malonaldehyde. In brief, although the both intramolecular proton transfers look similar, the changing features of both shape and frontier electron density along IRC routes are quite distinct, even opposite.