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Analysis of the I3C n.m.r. spectrum of 2-methoxytetrahydropyran [(I ) + (2)] in the range 143 to 165 K, and of the H n.m.r. spectrum of the equilibrated mixture of cis-and trans-2-methoxy-4-methyltetrahydropyran at 245 and 273 K gives [(2)]/[(1)] ca. 0.26, AH0 ca. 0, and ASo[(l) -+ (Z)] ca.-2.7 cal K-I mol-1 ( -1 1.3 J K-I mol-l) for the solvent CFCI3-CDCI3 (85:15 v/v); the smaller entropy of the equatorial conformation is consistent with a stronger exo-anomeric effect in that conformation.

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