The ortho-hydroxy-ortho′-formyl biaryl/lactol equilibrium: Quantumchemical studies on structure and dynamics

The equilibrium between the lactol-bridged biaryls 3 and the ring opened hydroxy aldehyde isomers 4 as well as their atropisomerization are investigated by quantumchemical calculations. The suitability of semiempirical and different modern ab initio methods is validated by comparison with experimentally observed equilibria and crystallographic data. It is shown that for the description of the equilibrium between 3 and 4 Hartree-Fock ab initio methods lead to a significant improvement compared with semiempirical methods. Furthermore, the consideration of solvent effects by using AM1-SM4, PM3-SM4 and PM3-SM3 gives satisfying results in the description of the equilibrium investigated. (C) 1998 Elsevier Science Ltd. All rights reserved.