The effect of unconventional hydrogen bonding in the stability of keto forms of 2- Bromo-1,3-diphenylpropane-1,3-dione

By far less, researches have evidenced the existence of numerous new types ofinteractions, which may be classified as unconventional hydrogen bonds; such as dihydrogenbonds or blue-shifting hydrogen bonds. One of the main tools often recently applied instudies on these unusual bonds is the ‘‘Atoms In Molecules’’ theory (AIM) [1]. β-diketonesare a well-known group of tautomeric compounds that are widely employed in organic andinorganic chemistry. The complexity of α-substituent effects come into view when thesequence of the enol contents on going from Z = Cl to Z = Br and to Z = I is considered.Substitution of Cl at α-position enhance the enol content whereas Br and I considerablydecrease the enol content [2]. 2-Bromo-1,3-diphenylpropane-1,3-dione (BrDBM) could be aninteresting candidate for study of keto-enol tautomerization, since existing of two phenylgroups in the β-positions highly increase the enol content whereas substitution of Br in the α-position decreases the enol content. The IR spectroscopy study indicated that BrDBM iscompletely in the keto form in solid phase [3]. The X-ray diffraction study indicates that twoketo forms exist in the crystals of BrDBM [4]. The aim of the present work is study thestability of keto forms in BrDBM by using DFT, NBO, and AIM calculations.