Effect of hydroxyl and carbonyl groups on long‐range proton—carbon coupling constants

Abstract

AbstractLong‐range 1H13C coupling constants were measured for some simple, rigid model compounds containing hydroxyl, bromine or carbonyl groups. These were performed using the recently proposed selective J‐resolved SPININEP and SDEPT‐2D experiments. The geminal and vicinal heteronuclear coupling constant values were analysed in terms of the nature of substituent, the position along the coupling path and the orientation of the substituent relative to the bounds. In some cases, through‐space interactions of the substituent group were also observed. Sizeable substituent effects are associated with the electronegativity and lone pair of the oxygen nucleus in the hydroxyl and carbonyl systems. In addition, the π‐system of the carbonyl group may also be important. Such substituent effects may be as large at ±5 Hz. Since nJCH constants rarely exceed 10 Hz, these effects can produce important deviations in nJCH magnitudes and therefore are essential for applications to stereochemical and conformational analysis.