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Experimental and theoretical studies of the products of addition–elimination reactions between benzil dihydrazone and three isomeric chlorobenzaldehydes
Author(s) -
Liu YunNa,
Cheng ShuangShuang,
Wang Chao,
Xing DianXiang,
Liu Yun,
Tan XueJie
Publication year - 2015
Publication title -
acta crystallographica section c
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.304
H-Index - 17
ISSN - 2053-2296
DOI - 10.1107/s2053229615010682
Subject(s) - triclinic crystal system , chemistry , monoclinic crystal system , schiff base , crystallography , benzil , density functional theory , orthorhombic crystal system , homo/lumo , space group , supramolecular chemistry , molecule , intermolecular force , crystal structure , computational chemistry , x ray crystallography , organic chemistry , diffraction , catalysis , physics , optics
A series of mono‐ and di‐Schiff bases formed between benzil dihydrazone {BDH; systematic name: (1 Z )‐[(2 E )‐2‐hydrazinylidene‐1,2‐diphenylethylidene]hydrazine} and three isomeric chlorobenzaldehydes were designed and synthesized to be used as model compounds to help to explain the reaction mechanisms for the formation of Schiff bases. These compounds are 1‐(2‐chlorobenzylidene)‐2‐{2‐[2‐(2‐chlorobenzylidene)hydrazin‐1‐ylidene]‐1,2‐diphenylethylidene}hydrazine (BDHOCB), and the 3‐chloro (BDHMCB) and 4‐chloro (BDHPCB) analogues, all having the formula C 28 H 20 Cl 2 N 4 . Surprisingly, only di‐Schiff bases were obtained; our attempts to push the reaction in favour of the mono‐Schiff bases all failed. Density functional theory (DFT) calculations were performed to explain the trend in the experimental results. In the case of the systems studied, the type of Schiff base produced exhibits a clear dependence on the HOMO–LUMO energy gaps (Δ E HOMO–LUMO ), i.e. the product is mainly governed by its stability. The compounds were characterized by single‐crystal X‐ray diffractometry, elemental analysis, melting point, 1 H NMR and 13 C NMR spectroscopy. The structural features of the three new Schiff bases are similar. For instance, they have the same chemical formula, all the molecules have a symmetrical double helix structure, with each Ph—C=N—N=C—Ph arm exhibiting an anti conformation, and their supramolecular interactions include intermolecular π–π and weak C—H...π stacking interactions. The crystal systems are different, however, viz. triclinic (space group P ) for BDHPCB, monoclinic (space group P 2 1 / n ) for BDHOCB and orthorhombic (space group Pnna ) for BDHMCB.