Heterocycles. CLXIX. Barriers to rotation in some N,N ‐Dimethyl‐ N ′‐heteroaryl, N,N ‐Diethyl‐ N ′‐heteroaryl‐substituted formamidines and N,N ‐Dimethyl‐ N ′‐heteroaryl‐substituted acetamidines

The free energies of the rotational barriers, ΔG*, about CHNMe 2 bond in N ′‐heteroaryl N,N ‐dimethylformamidines (A), about CHNEt 2 bond in N ‐heteroaryl N,N ‐diethylformamidines (B), and about C(Me)NMe 2 bond in N ′‐heteroaryl N,N ‐dimethylacetamidines (C) have been found to be in the range 17.5–20.1 kcal/mole for type A, 18.8–21.6 kcal/mole for type B and 13–14 kcal/mole or below for type C of compounds, respectively. The compounds of the types A and B exist in the forms IIa, IIIa, IV, V, and VI, while the compounds of the type C exist in the forms IIb and IIIb.