Static and Dynamic Stereochemistry of Chloropentakis(dichloromethyl)benzene

Chloropentakis(dichloromethyl)benzene (2) was synthesized by photochlorination of chloropentamethylbenzene. The barrier for internal rotation of the side chains was measured by the spin saturation transfer technique and by the coalescence approximation. Empirical force field calculations show that the preferred conformation is the all geared, in agreement with the NMR data, and that the mechanism of topomerization involves stepwise rotation of the side chains. The calculations closely reproduce the topomerization barrier (experimental 20 kcal mol^-1; calculated 22 kcal mol^-1).