Abstract 1, 3, 5-Trineopentylbenzenes (TNB) with one or two benzylic substituents in each neopentyl group were synthesized. The substituents were F, Cl, Br, J, OCH 3, OCOCH 3, OSi (CH 3) 3 and CH 3 and, in cases of disubstitution, F, Cl, Br, CH 3 and Cl, CH 3 and Br and [BOND] SCH 2 CH 2 S [BOND]. Barriers to internal C sp3 [BOND] C sp2 (aryl) and C sp3 [BOND] C sp3 rotation were estimated by 13 C and 19 F NMR band shape methods. ...