Asymmetric Imine N-Inversion in 3-Methyl-4-Pyrimidinimine. Molecular Dipole Analysis of Solvation Effects

Abstract

The thermal (E)/(Z)-isomerization of 3-methyl-4-pyrimidinimine, 3MePMI, has been studied in the gas phase at MP2/6-31G* and with the inclusion of medium effects using the polarizable continuum method, PCM(MP2/6-31G*), and the solvation model density method, SMD(MP2/6-31G*). For the free molecule and for 3MePMI in each of 14 solvents, the structures were determined of the (E)- and (Z)-isomers, of the transition state structure for isomerization ITS by asymmetric N-inversion, and of the second-order saddle point structure (SOSP) associated with in-plane N-inversion. The results predict a reduction of the (E)-isomer preference energy of 3MePMI, an increase of the deformation energy ΔEdef = E(SOSP) - E(ITS), and an increase of the activation barrier Eact(Z → E) with increasing solvent polarity. Electronic effects associated with N-inversion are analyzed using molecular orbital theory, results of population analysis, and electrostatic potential maps. The molecular dipole moments are superior parameters for the description of electronic relaxation in the imine basin during N-inversion. In particular, the analysis of dipole moments explains the compatibility of the increase of local CN polarity during N-inversion with the negative solvation effect on the activation barrier.

Department(s)

Chemistry

Keywords and Phrases

Activation Barriers; Deformation Energy; Electronic Effects; Electronic Relaxation; Electrostatic Potential Maps; Free Molecules; Gasphase; In-Plane; Medium Effect; Molecular Dipole; Molecular Dipole Moment; Molecular Orbital Theory; MP2/6-31G; Polarizable Continuum Methods; Population Analysis; Saddle Point; Second Orders; Solvation Effect; Solvation Models; Solvent Polarity; Thermal; Transition State Structure; Electric Dipole Moments; Isomerization; Isomers; Molecular Orbitals; Nitrogen Compounds; Plants (Botany); Solvation; Solvents; Activation Analysis; 3 Methyl 4 Pyrimidine (3h) Imine; Carbon; Chloroform; Hydrogen; Imine; Nitrogen; Pyrimidine Derivative; Unclassified Drug; Aqueous Solution; Chemical Analysis; Chemical Bond; Chemical Reaction; Chemical Structure; Dipole; Energy; Gas; Hydrogen Bond; Isomer; Isomerization; Molecular Electronics; Molecular Stability; Polarization; Static Electricity; Thermodynamics

International Standard Serial Number (ISSN)

0022-3263; 1520-6904

Document Type

Article - Journal

Document Version

Citation

File Type

text

Language(s)

English

Rights

© 2011 American Chemical Society (ACS), All rights reserved.

Publication Date

01 May 2011

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