Different hydrogen-bonded chains in the crystal structures of three alkyl N-[(E)-1-(2-benzyl­idene-1-methyl­hydrazin­yl)-3-hy­droxy-1-oxopropan-2-yl]carbamates

The crystal structures of three methyl­ated hydrazine carbamate derivatives prepared by multi-step syntheses from l-serine are presented, namely benzyl N-{(E)-1-[2-(4-cyanobenzylidene)-1-methylhydrazinyl]-3-hydroxy-1-oxopro­pan-2-yl}carbamate, C(20)H(20)N(4)O(4), tert-butyl N-{(E)-1-[2-(4-cyanobenzylidene)-1-methylhydrazinyl]-3-hydroxy-1-oxopropan-2-yl}carbamate, C(17)H(22)N(4)O(4), and tert-butyl N-[(E)-1-(2-benzylidene-1-methylhydrazinyl)-3-hydroxy-1-oxopro­pan-2-yl]carbamate, C(16)H(23)N(3)O(4). One of them shows that an unexpected racemization has occurred during the mild-condition methyl­ation reaction. In each crystal structure, the mol­ecules are linked into chains by O—H⋯O hydrogen bonds, but with significant differences between them.