Carbon-13 Nuclear Magnetic Resonance Studies of ortho-Substituted Anisoles and Diphenyl Ethers

Carbon-13 n.m.r. chemical shifts for 8 anisoles and 15 diphenyl ethers are reported. para-Carbon shieldings are found to be sensitive to the degree of steric interference to conjugative electron release by the ethereal oxygen atom. An empirical correlation between the para-carbon shifts and the average twist angle of the phenyl rings from a reference plane has been developed. Satisfactory agreement has been found between the angles of twist derived from carbon chemical shifts and those based on other physical measurements.