The methyl ester of methanimidic acid or O-methylformimidate exists in E and Z stereoisomers and anti-and synperiplanar conformations of C s symmetry, Fig. , as delineated by Lumbroso and Papparlardo in early SCF-MO/4-31G calculations who found that the (E, ap) form is the most stable. A conclusion which is reinforced by G4 calculations which ranks their ∆ f H -• (0 K) as follows: