87938-08-7Relevant academic research and scientific papers
Equilibrium Configurations of Azines of Esters
Keus, Diane,Warkentin, John
, p. 3466 - 3469 (2007/10/02)
The equilibrium configuration of hydrazonates (ester azines) such as R2O(R1)C=NN=C(R3)2 (2) and 2O(R1)C=N>2 (3) is to found to be that in which the alkoxy group is anti (E configuration) even if the alkyl group (R1) is larger than the alkoxy group.This is the same as the configuration of imidates ( CH3O(R)C=NCH3 ) and opposite to the configuration observed for azines, hydrazones, and semicarbazones of aldehydes and ketones, where the more bulky group occupies the anti position.With R2=CH3 or CH2CH3, R1 groups smaller than tert-butyl do not force the hydrazonates into the Z configuration and even in the case R1=tert-butyl (R2=CH3), the E isomer predominates in the two-component system (2) at equilibrium.Similarly, in the three component system (3) (R2=CH3, R1=C(CH3)3) the order of predominance at equilibrium is E,E,>E,Z,>Z,Z.It is concluded that dipole alignment is an important factor stabilizing the E configuration and that there may also be some destabilization of the Z configuration resulting from repulsions between nonbonded electrons at nitrogen and at oxygen.Both factors are illustrated above with the isomers of 2.
