The Baker-Nathan Order: Hyperconjugation or a Solvent Effect?

Abstract

The electronic effect of alkyl groups attached to an aromatic ring has been determined under varying conditions of electron demand by measuring their influence on the ¹³C n.rn.r. chemical shifts of the β-carbon of β-substituted styrenes. When the group, is para to the side chain their ability to donate electrons follows the order Me > Et > Prⁱ > Bu^t, and, when meta, Bu^t > Prⁱ > Et > Me. This order is the same in CCl₄, CDCl₃, Me₂SO and EtOH solvent, the results suggesting that the Baker-Nathan effect is a hyperconjugative rather than solvation phenomenon.