COMMENT ON NEMATIC MIXTURE METHODS FOR THE DETERMINATION OF CHEMICAL-SHIFT ANISOTROPY

Two recent investigations of the C-13 and( 1)H nuclear magnetic shield ing anisotropies of chloroform by liquid crystal NMR methods are compa red. It is shown that the difference of results between the two cannot be attributed to the difference in the ENEMIX and NEMIX methods emplo yed. The interpretation of results as being affected by hydrogen bondi ng of chloroform with the C=N groups of the ZLI1167 liquid crystal sol vent is supported by ab initio calculation of the H-1 NMR association shift of CHCl3 in the chloroform-hydrogen cyanide complex. A model cal culation is shown to reproduce the ab initio result to good accuracy. (C) 1998 Elsevier Science B.V. All rights reserved.