Mechanism of the uncatalysed syn–anti-isomerization of imine systems. Part IV. A theoretical study of the influence of substituents

Abstract

Extended Hückel (Hoffmann) calculations have been performed for the ‘lateral shift’syn–anti-isomerization of seven simple imine derivatives H₂CN–X (X = H, Me, NH₂, OH, F, Cl, and Br). The energy-barrier values obtained are in satisfactory agreement with the experimental data (except those for X = Cl or Br). The computed ‘reduced overlap population’ for the N–X bond, and the ‘gross atomic population’ values for the nitrogen atom, together with previous data show that our hypothesis about the influence of the N-bonded substituent is valid: i.e., the isomerization energy barrier isgreatest for substituents with a strong –l(inductive) but no –M(mesomeric) effect.