Novel direct access to enantiomerization barriers from peak profiles in enantioselective dynamic chromatography: Enantiomerization of dialkyl‐1,3‐allenedicarboxylates

The axially chiral allenes dimethyl‐1,3‐allenedicarboxylate 1 and diethyl‐1,3‐allenedicarboxylate 2 show characteristic plateau formation during enantioselective GC separation on the chiral stationary liquid phase Chirasil‐β‐Dex. The elution profiles, obtained from temperature‐dependent dynamic GC (DGC) experiments ( 1 : 100–140°C; 2 : 110–150°C) were evaluated with the recently derived approximation function (AF) $k_1^{approx} = f(t^{A}_{R}, t_R^B, w^A_h, h_{plateau}, N)$ to yield the enantiomerization rate constant directly k 1 . These values were compared with those obtained by computer‐aided simulation with ChromWin. The Eyring activation parameters of the experimental interconversion profiles were determined to be: Δ G # (298.15 K) = 103.6 ± 0.9 kJ mol −1 , Δ H # = 44.7 ± 0.4 kJ mol −1 , Δ S # = −198 ± 7 J K 1 mol −1 for dimethyl‐1,3‐allenedicarboxylate 1 , and Δ G # (298.15 K) = 103.5 ± 1.1 kJ mol −1 , Δ H # = 44.7 ± 0.5 kJ mol −1 , Δ S # = −197 ± 9 J K −1 mol −1 for diethyl‐1,3‐allenedicarboxylate 2 . The approximation function (AF) presented here allows the fast determination of rate constants k 1 and activation barriers of enantiomerization Δ G # from chromatographic parameters without extensive computer simulation. Chirality 14:465–470, 2002. © 2002 Wiley‐Liss, Inc.