EFFECT OF HYDROXYL AND CARBONYL GROUPS ON LONG-RANGE PROTON CARBON COUPLING-CONSTANTS

Long-range H-1-C-13 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 heteronucl ear coupling constant values were analysed in terms of the nature of s ubstituent, the position along the coupling path and the orientation o f the substituent relative to the bounds. In some cases, through-space interactions of the substituent group were also observed. Sizeable su bstituent effects are associated with the electronegativity and lone p air of the oxygen nucleus in the hydroxyl and carbonyl systems. In add ition, the pi-system of the carbonyl group may also be important. Such substituent effects may be as large at +/- 5 Hz. Since (n)J(CH) const ants rarely exceed 10 Hz, these effects can produce important deviatio ns in (n)J(CH) magnitudes and therefore are essential for applications to stereochemical and conformational analysis.