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 > But, and, when meta, But > 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.