ORIGINAL RESEARCH A comprehensive theoretical study of tautomeric and conformeric preferences, intramolecular hydrogen bonding, and p-electron delocalization in b-selenoaminoacrolein with its thio and oxo analogs A. Nowroozi • S. Sarhadinia • E. Masumian • E. Nakhaei Received: 30 December 2013 / Accepted: 2 February 2014 Ó Springer Science+Business Media New York 2014 Abstract The quantum chemical study of various aspects of b-selenoaminoacrolein, b-thioaminoacrolein, and b- aminoacrolein was performed at various theoretical levels, HF, B3LYP, and MP2 with 6-311??G(3df,3pd) basis set, and the equilibrium conformations were determined. According to these calculations, tautomeric and confor- meric preferences, intramolecular hydrogen bond, and p-electron delocalization (p-ED) were investigated. Among tautomers, enaminic tautomers have extra stability with respect to the iminic ones, with and without p-ED. All of the criteria predict that the origin of tautomeric prefer- ences is mainly due to the greater p-ED in the framework of enaminic tautomers. Moreover, our computational results reveal that the formation of intramolecular hydro- gen bond is accepted as the origin of conformational preferences. According to the hydrogen bond descriptors, such as HB energy, geometrical, spectroscopic, topologi- cal, and molecular orbital parameters, various HB energy orders were found and interpreted. On the other hand, p- ED of chelated rings were measured using various indices, such as q, HOMA, NICS, PDI, ATI, and FLU p index, and various orders were found. Finally, the orders of hydrogen bond strength and p-ED, obtained by some of indices, support the resonance assisted hydrogen bond theory. Keywords: b-Selenoaminoacrolein  Intramolecular hydrogen bond  p-electron delocalization  AIM and NBO Introduction The resonance assisted hydrogen bond (RAHB) is one of the most important concepts in structural chemistry [1–3]. In RAHB systems, the intramolecular hydrogen bond (IMHB) and p-electron delocalization (p-ED) are strongly coupled. However, the RAHB idea has been the subject of various challenges [4–7], and it reasonably well describes the IMHB of b-dicarbonyls compounds. Over the years, the IMHB in some of simple RAHB rings, such as malonal- dehyde and its derivatives, have been extensively investi- gated, theoretically and experimentally [8–10]. Selenium is an essential trace element with wide range of chemical, physical, and biological applications. Because of these numerous usage, organoselenium compounds have kept the attention of many researchers and scientists [11– 16]. b-selenoaminoacrolein (SAMAC) is the simplest selenium derivatives of b-aminoketon compounds. The replacement of oxygen by selenium in the b-aminoacrolein (AMAC) leads to the production of SAMAC. The molec- ular structure of SAMAC is similar to the parent molecule, except that SAMAC has C=Se instead of C=O function group. Therefore, it can play a role like of AMAC in the selenoaminoketon compounds chemistry. Proton transfer and hydrogen bond are two aspects of SAMAC chemistry. Proton transfer in the tautomeric equilibriums, such as selenal (C–C=Se) $ selenol (C=C–Se–H) and imine (C– C=NH) $ enamine (C=C–NH 2 ), creates selenalenamine (SAA), selenolimine (SOI), and selenalimine (SAI) tau- tomers (Fig. 1). In some of the mentioned tautomers, the suitable configuration of functional groups can lead to Se– HN and N–HSe hydrogen bonds which are coupled with p-ED and make RAHB systems. Small RAHB systems can be used as models for rec- ognition of the behavior of complex biological molecules. Electronic supplementary material The online version of this article (doi:10.1007/s11224-014-0412-8) contains supplementary material, which is available to authorized users. A. Nowroozi (&)  S. Sarhadinia  E. Masumian  E. Nakhaei Department of Chemistry, Faculty of Science, University of Sistan and Baluchestan, P.O. Box 98135-674, Zahedan, Iran e-mail: anowroozi@chem.usb.ac.ir 123 Struct Chem DOI 10.1007/s11224-014-0412-8