Resolution by chiral hplc of the stable free radical perchlorotriphenylmethyl: Thermodynamic and chiroptical properties

The perchlorotriphenylmethyl radical (PTM) shows enantiomerism due to restricted internal rotations. Several chiral stationary phases have been tested in different conditions for the resolution of PTM by HPLC. Only poly(triphenylmethyl methacrylate) provided sufficient resolution for carrying out a micropreparative scale separation. Racemization of (+)‐ and (−)‐PTM was monitored polarimetrically as a function of time. The process was found to follow strict first‐order kinetics. The value of ΔG#303.8 = 23.6 Kcal · mol−1 agrees with that determined previously by HPLC with the stopped flux technique (Crespo, Doctoral Thesis, CETS Institut Químic de Sarrià, 1991). Following the helicity rules in the circular dichroism spectrum, (+)‐PTM can be assumed to have (P) configuration and (−)‐PTM (M) configuration. © 1995 Wiley‐Liss, Inc.