Acetaldehyde azine, $CH X_{3} - CH = N - N = CH - CH X_{3}$ , is a symmetrical molecule with two $C = N$ bonds. Considering only the configurations of the two $C = N$ bonds (ignore conformations about the $N - N$ bond), how many geometrical isomers exist?

Answer: A

Each

C = N

has

H

and

CH X_{3}

on carbon and the other nitrogen versus a lone pair on nitrogen, so each is stereogenic (

E

Z

). Four combinations arise, but

(E, Z)

and

(Z, E)

are the same compound by the symmetry of the molecule, leaving

(E, E)

(Z, Z)

and

(E, Z)

3