C-13 NMR RELAXATION STUDIES OF CYCLOALKYLIDENE BISPHENOLS, METHYL ETHERS, AND SIMPLE BENZOATE ESTERS IN SOLUTION - DIFFERENT AVERAGE CORRELATION TIMES FOR DIPOLE-DIPOLE AND CHEMICAL-SHIFT ANISOTROPY RELAXATION

Carbon-13 NMR relaxation of a series of cycloalkylidene bisphenol monomers and related compounds has been examined. The following monomers were studied: cyclohexylidene bisphenol and its dimethyl ether, 4-tert- butylcyclohexylidene bisphenol and its dimethyl ether, cyclopentylidene bisphenol, phenyl 1,3,5-tribenzoate, and triphenyl 1,3,5-benzenecarboxylate. The motional properties of these compounds in solution have been determined from,their carbon T-1 relaxation times. Phenyl motion is generally faster than overall molecular tumbling except for the axial group of tBBP6. The order of phenyl mobilities was TPBC > PTB > tBBP6 eq similar to BP5 > BP6 > tBBP6ax. In PTB and TPBC dipole-dipole (DD) coupling relaxes the protonated carbons, and chemical shift anisotropy (CSA) is a major contributor for substituted carbons, especially at 150 MHz. Different average diffusional correlation times were found for DD and CSA relaxation for the fast internal phenyl motion. Small-angle rotational diffusion about the phenyl C-2 axis was inferred to be faster than overall tumbling, but complete rotational averaging was slower. Three bond C-13-H coupling constants were measured for PTB and TPBC. The C-13 isotope-induced shift for H2 of PTB was 2.0 ppb. The activation energy for ring inversion in BP6 was measured to be 11 +/- 1 kcal/mol.