As shown in Fig. , the diazirine adopts a nearly coplanar conformation in its ground state, in which the φCF 3 -C diazirine -C ipso -C ortho dihedral angle is approximately 10°. The coplanar conformer was favoured over the corresponding 90° structure by ca. 1.8 kcal/mol. By contrast, the saturated diaziridine molecule preferentially adopted a twisted conformation (φ = 130°), in which the steric repulsions within the molecule were minimized.