Coupling constants nitrogen-15-nitrogen-15 and nitrogen-15-hydrogen in phenylhydrazones forming hydrogen bond

Abstract

Absolute values of the coupling constants 1J(15N15N), 1J(15NH) of six phenylhydrazones forming hydrogen bond, 2J(15N15NH) of four, and 4J(15NH) of two phenylhydrazones have been determined. Three coupling constants 1J(15N15N) have been obtained from the nitrogen-15 monolabelled compounds by measuring the other nitrogen at natural abundance. The coupling constants 2J(15N15NH) have been measured with the nitrogen-15 doubly labelled compounds, because in the arrangement 15N14NH there exists a broadening of the proton signal due to nitrogen-14. Absolute values of the coupling constants 1J(15N15N) of the phenylhydrazones forming hydrogen bond to the ester group are smaller ( 10.8 Hz) than those of the phenylhydrazones having hydrogen bond to carbonyl group ( 11.1 Hz). The coupling constants 2J(15N15NH) have a value 2.4 ± 0.2 Hz. The value of 1J(15N15N) of 1-phenylazo-2-naphthalenol decreases with increasing content of hydrazone form. The values of 2J(15N15NH) of this compound are within 1.2 to 1.6 Hz.