Competitive H-bonding synthons in organic hydrazides

A theoretical, statistical and crystallographic analysis of the H-bonding patterns in organic monohydrazides is presented. The theoretical analysis has shown that the conformation of the hydrazido group with the two amino H atoms staggered with respect to the amide bond is energetically more favoured. Assuming this conformation, four intermolecular H-bonding patterns can be reasonably foreseen, two forming chains, C(4) and C2 2(8), and two forming rings, R2 2(10) or R2 2(6). The frequency of occurrence of the four patterns in the set of crystal structures of hydrazides retrieved from CSD was evaluated. In particular, it was found that the four motifs are present in 79% of the total number of crystal structures of hydrazides found in CSD. Finally, the crystal structures of four new benzohydrazides having additional H-bonding donor or acceptor groups in the para position are presented and discussed with reference to the H-bonding patterns.