EXCEPTIONALLY LARGE C-13-C-13 COUPLING-CONSTANTS OF COMPOUNDS CONTAINING A CF3 GROUP

Coupling constants, 1J(13C,13C), of compounds containing a CF3 group are reported. The values for the coupling of the CF3 carbon with the neighbouring carbon are exceptionally large. In a series of compounds in which the CF3 group is bonded to an sp3, sp2 or sp carbon the 1J(C,C) values show a good linear correlation with the product of the s characters of the two orbitals forming the CC bond. Furthermore, compounds containing a CCl3 group have been measured. A correlation of the 1J(CC) values with the sum of the group electronegativities in compounds of the CX3‐CY3 type is found. The results for compounds containing highly electronegative substituents suggest a contribution to the CC coupling from a relatively large variation of the valence‐shell s‐orbital density at the carbon nucleus, Sc2(0). Additional 13C and 19F NMR data of the compounds are presented. Copyright © 1990 John Wiley & Sons, Ltd.