Nuclear Magnetic Resonance Study of the Effect of the Hydrogen Bond on the Internal Rotation of Biphenyls

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Abstract
Internal rotation about the pivot bond of several biphenyl derivatives has been studied by means of the nuclear magnetic resonance technique using non-identical chemical shifts of the two methyls in the isopropyl group which is located close to the center of dissymmetry. The results with the 2-methoxy and 2-hydroxy derivatives are compared. The solvent effect is marked in 2-hydroxy derivatives. These results, together with the substituent effect, indicate that the fact that the energy of activation for rotation about the pivot bond of the 2-hydroxy derivatives is a little higher than the corresponding methyl ether may be attributed to the stabilization of the ground state resulting from the presence of intramolecular O–H···π interaction. The infrared data agree with the above conclusion.