C-C bond order parameters from H-2 and C-13 solid-state NMR

In this letter we demonstrate the accuracy of the C-k-1-C-k bond order parameters, S-k(CC), when determined from the C-k-D (H-2) bond order parameters, S-k(CD), as experimentally measured on a fully deuterated chain. Two different approaches were taken to determine the C-1-C-2 bond order parameter, S-2(CC), of a palmitic acid chain (k = 1-16) embedded in a Liquid crystal. First, solid-state 2H NMR experiments were performed on the perdeuterated chain in order to obtain its C-D bond order parameter profile. The recursion relation, -2S(k)(CD) = S-k(CC) + S-k+1(CC), between consecutive S-k(CC), where k stands for the labeled carbon position was used to calculate S-2(CC). Second, having included a quantity of palmitic acid specifically C-13-labeled at the C-1 and C-2 positions, the dipolar coupling between these carbons was measured using one- and two-dimensional C-13 solid-state NMR spectroscopy. This coupling provides a direct and independent measure of S-2(CC), the order parameter of interest. Both methods agree within 4%.