Crystal and Molecular Structures and Acid–Base Equilibria of N-(4-Chlorophenyl)-2-Benzoylethylamine and Bis[3-(o-Chlorophenyl)-1-Phenylaminopropyl]diazene

N-(Phenyl)-2-benzoylethylamine ( I ), N-(4-chlorophenyl)-2-benzoylethylamine ( II ), and N-(2-chlorophenyl)-2-benzoylethylamine hydrazone ( III ) were synthesized in the crystalline state. The heating of ethanolic solutions of compound III at reflux gave dimeric bis[3-( о -chlorophenyl)-1-phenylaminopropyl]diazene ( IV ). The crystal and molecular structures of compounds II and IV were determined by X-ray diffraction. In the crystal of II , the molecules are packed in stacks in a head-to-head fashion stabilized by intermolecular hydrogen bonds involving carbonyl oxygen atoms and hydrogen atoms at nitrogen. Compound IV is composed of two independent bis[3-( о -chlorophenyl)-1-phenylaminopropyl]diazene molecules as structural units. Each structural unit is a centrosymmetric dimer. There are no hydrogen bonds in compound IV . Acid–base equilibrium reactions were studied by spectrophotometric titration. The protonation constants are 4.68 ± 0.14 for I and 4.11 ± 0.13 for II .