By far less, researches have evidenced the existence of numerous new types of interactions, which may be classified as unconventional hydrogen bonds; such as dihydrogen bonds or blue-shifting hydrogen bonds. One of the main tools often recently applied in studies on these unusual bonds is the ‘‘Atoms In Molecules’’ theory (AIM) [1]. β-diketones are a well-known group of tautomeric compounds that are widely employed in organic and inorganic chemistry. The complexity of α-substituent effects come into view when the sequence 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 considerably decrease the enol content [2]. 2-Bromo-1,3-diphenylpropane-1,3-dione (BrDBM) could be an interesting candidate for study of keto-enol tautomerization, since existing of two phenyl groups 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 is completely in the keto form in solid phase [3]. The X-ray diffraction study indicates that two keto forms exist in the crystals of BrDBM [4]. The aim of the present work is study the stability of keto forms in BrDBM by using DFT, NBO, and AIM calculations.

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