Table 1. Favored Development Strategy As a Function of Atropisomer Interconversion Barrier (ΔG^⧧)^a.

Interconversion barrier (ΔG⧧; kcal/mol)	Isomerization time (1% conversion; 23 °C)	Development strategy
<20 (‘Class 1’)	<1 s	Rapidly equilibrating mixtureb
20–30 (‘Class 2’)	1 s to 9 months	Case dependent; disfavored for developmentc
>30 (‘Class 3’)	>9 months	Single atropisomerd

^aInterconversion barrier classification and development strategies taken from refs (6) and (20).

^bInterconversion rapid versus pharmacological and manufacturing processes.

^cInterconversion on the same time scale as pharmacological and manufacturing processes.

^dInterconversion slow versus pharmacological and manufacturing processes.