Electronic circular dichroism spectroscopy of 1-(R)-phenylethanol: the "sector rule" revisited and an exploration of solvent effects

The sensitivity of the electronic circular dichroism (ECD) of a chiral molecule to structural and environmental changes has been investigated using 1-(R)-phenylethanol (1-PE) as the benchmark solute and cyclohexane and water as the trial solvents. Rotatory strengths associated with the π → π* (1Lb) electronic transition have been calculated ab initio for: (a) isolated 1-PE, as a function of the dihedral angles within its chiral side chain and between the side chain and the aromatic ring: these confirm the validity of the empirical “sector rule” but with the signs reversed; (b) the singly and doubly hydrated clusters of 1-PE, isolated in the gas phase; (c) 1-PE and its singly and doubly hydrated clusters embedded in a polarizable dielectric continuum; and (d) 1-PE in an aqueous solution interacting with the local hydration shell and with the polarizable dielectric continuum, using averaged solute structures computed from the fluctuating solute and solvent configurations generated via molecular dynamics simulations.