Abstract
This contribution sets out to compute thermochemical and geometrical parameters of the complete series of chlorinated isomers of thiophene based on the accurate chemistry model of CBS-QB3. Herein, we compute standard entropies, standard enthalpies of formation, standard Gibbs free energies of formation, and heat capacities. Our calculated enthalpy values agree with available limited experimental values. The DFT-based reactivity descriptors were used to elucidate the site selectivity for the chlorination sequence of thiophene. The relative preference for chlorination was found to be in accord with the thermodynamic stability trends inferred based on the H scale. Calculated Fukui indices predict a chlorination sequence to ensue as follows: 2-chloro → 2,5-dichloro → 2,3,5-trichloro → 2,3,4,5-tetrachlorothiophene.
Highlights
Thiophene (C4H4S) is a heterocyclic organic compound with a five-membered ring similar to cyclopentadiene with replacement of a -CH2- group by sulfur atom [1]
Chlorothiophene isomers may be used in the synthesis of many important organic compounds [6,7,8]
[10], chlorination of 2-chlorothiophene yielded a dichlorothiophene fraction composed of high percent of 2,5-dichloro thiophene and 2,3-dichlorothiophene, 2,3, 2,4, and 3,4dichlorothiophenes were formed largely by dehydrohalogenation of 2,3,4,5-tetrachlorothiolane and not by substitution. 2,5-Dichlorothiophene was formed by substitution
Summary
Thiophene (C4H4S) is a heterocyclic organic compound with a five-membered ring similar to cyclopentadiene with replacement of a -CH2- group by sulfur atom [1]. Medicinal chemistry approaches to minimize the bioactivation potential of thiophenes often include substitution at the α-carbon position to provide a potential site for metabolism. Such thiophene derivative that is often used in medicinal chemistry is the α-chlorothiophene, and there are several examples of marketed drugs containing this moiety such as tioconazole, lornoxicam, and rivaroxaban [4]. The effects of the number and the position of the chlorine atoms on the properties of the thiophene ring for the chlorothiophenes have been studied theoretically by the CBS-QB3 composite method [14]. The focus in this study is on acquiring standard entropies, heat capacities, enthalpy, and the free energy barrier for the addition of Cl to the ring-carbon sites at selected temperature for the optimized structures of chlorinated thiophene compounds which are calculated
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