ORIENTAL JOURNAL OF CHEMISTRY www.orientjchem.org An International Open Free Access, Peer Reviewed Research Journal ISSN: 0970-020 X CODEN: OJCHEG 2017, Vol. 33, No. (3): Pg. 1265-1275 Solvent Effects on the Mechanistic of Ketene and Halogenated Ketene Cycloadditions with Cyclopentadiene: A DFT Study NASRIN FARAHANI 1 and SEYED MAJID MUSAVI 2 * 1 Department of Chemistry, Buinzahra Branch, Islamic Azad University, Buinzahra, Iran. 2 Department of Chemistry, Shahr-e- Qods Branch, Islamic Azad University, Tehran, Iran *Corresponding author E-mail: moosavi_majid@yahoo.com http://dx.doi.org/10.13005/ojc/330326 (Received: January 28, 2017; Accepted: March 19, 2017) ABSTRACT The energetic and activation barriers for 4 possible [2+2] and [4+2] cycloadditions of ketene and dihaloketenes with cyclopentadiene are investigated at B3LYP/6-31G* level of theory. Three solvents including DMSO, CCl 4 and water, using the CPCM model, are considered and their results are compared to those of gas phase. The entire studied cycloadditions take place via clear asynchronous TSs. For the parent ketene, all solvents stabilize the reactants within the range of 9.4-13.7 kcal/mol and reduce the thermodynamic achievability of this reaction (∆E=-18.4, -10.9, -11.6 and -12.8 kcal/ mol for gas phase, CCl 4 , DMSO and H 2 O, respectively, for [2+2] across C=C) and the energy barriers are increased to the maximum of 6.1 kcal/mol. In contrast, for dihaloketenes all solvents make the thermodynamics less favorite by decreasing the exoergicity (within 1-5 kcal/mol), however, most of reaction pathways become kinetically favored by lowering the energy barriers (within 1-7 kcal/ mol) in the presence of polar solvents. The nonpolar solvent CCl 4 behaves like that of gas phase. Moreover, the preference of two-step cycloaddition via [3+3] sigmatropic rearrangement is reduced in the presence of solvents. The ultimate effect is pertaining to dichloroketen where it prefers the routine one-step cycloaddition pathway in H 2 O like that observed for the parent ketene. Keywords: Dihaloketene; Cycloaddition; Dielectric constant, Density functional theory, Dielse-Alder (Footnotes). INTRODUCTION Ketene chemistry started at the beginning of the previous century and subsequently it has extensively blossomed because of its theoretical significance as well as its utility in the organic synthesis 1,2 . The most characteristic reaction of ketenes is the cycloaddition, which is a powerful method to generate four membered ring heterocyclics. Ketenes mainly participate in [2+2] cycloadditions with a variety of dienophiles across the C=C, C=O, C=N, C=S, N=N, N=O, N=S, and P=N bonds 3 . Ketenes prefer to primarily form vinylcyclobutanone in the reaction with dienes which many reports argued their mechanisms by a single step [2+2] or by a [4+2] following a 3,3 rearrangement 4,9 . Despite the large number of reports on the gas phase cycloadditions of ketenes 10 theoretical investigations on the roles