![]() ![]() ![]() 29-33 Thus exploration of global and local reactivity descriptors to understand the mechanistic aspects for a cycloaddition reaction is worth important. 21-28 Moreover, recent literature study reveals that global and local descriptors are very useful and reliable tools for the predication of reaction mechanisms. In this context, for a long time, Domingo's group has been involved in the study of the DA reactions using these parameters to establish the polar character of cycloaddition. Moreover, the local reactivity descriptors provide a deep insight about the regioselectivity of cycloaddition reactions. Fukui function and local electrophilicity/nucleophilicity are extensively applied to probe the local reactivity and site selectivity. In this regards global electrophilicity, 8 chemical potential, 9-10 global hardness, 11-16 global softness, 10,17 and nucleophilicity 18-20 are highly successful in predicting the feasibility and polarity of cycloaddition reactions. Global and local reactivity descriptors evaluated using DFT are very much useful in explaining the behavior of reactant and products in an organic reaction. In this context, several reactivity descriptors have been proposed and used to analyze chemical reactivity and site selectivity. 7, has studied the Diels-Alder reaction of 2-furyl substituted 1-thia-1, 3-butadiene with various electrophilic olefins affording 2-furyl substituted 2H-thiopyran derivatives with high stereo selectivity.ĭensity functional theory (DFT) has been quite successful in explaining theoretical background of molecular properties and chemical concepts. Among these compounds the study of the behavior of carbon chalcogen double bonds (-C=S, -C=O, -C=Se) as dienes in hetero-Diels-Alder (HDA) reaction is worth important. In recent years, the chemistry of multiple bond compounds is quite interesting. Hetero-Diels-Alder reactions are the most powerful available methodologies for the construction of six membered heterocyclic derivatives which have wide applications in the area of medicinal, computational and synthesis. Keywords: Enaminothione, DFT, B3LYP-6-31G*, global and local reactivity descriptors These outcomes were found to be in exact correlation with the experimental outcomes achieved by Bogdanowicz et al. Regional nucleophilicity at the interacting site of diene were evaluated using local nucleophilicity descriptor N k. However, unsymmetrical dienophiles 16,18a-e and 21 have shown a preference towards a particular regioisomer and shown high regioselectivity during cycloaddition reaction. For symmetrical dienophiles viz., 2, 5, 8, 11a, 11b, 13 and 14 the local descriptors concentrates equally (50%) at both interacting sites, to allocate non-regioselective cycloadditions. The local descriptors based on Parr functions proposed by Domingo were found to be quite promising to explain the regioselectivity of cycloaddition processes. The results preluded that the polarity and charge transfer flow between diene and dienophiles was consistent with the global reactivity descriptors and substitutional pattern. * e-mail: mechanism of the Diels-Alder reaction of 1-(2-furyl)-3-(dimethylamino)-2-propene-1-thione with various dienophiles resulting in the formation of 2H-thiopyran derivatives were discussed by evaluating global and local electrophilicity and nucleophilicity descriptors for whole series of diene and dienophiles at B3LYP/6-31G* level of theory. VINITA SAHU, *,† PRATIBHA SHARMA, ‡ ASHOK KUMAR ‡ĭepartment of Chemistry, Alliance College of Engineering and Design, Alliance University, Bangalore, Karnataka, India This is true when either the diene or the dienophile is a meso compound (i.e., when either of the reactants is symmetrical).IMPACT OF GLOBAL AND LOCAL REACTIVITY DESCRIPTORS ON THE HETERO-DIELS-ALDER REACTION OF ENAMINOTHIONE WITH VARIOUS ELECTROPHILES The generic mechanism above implies that the dienophile can have either position relative to the diene, so long as one carbon binds with carbon 1 in the diene and the other carbon interacts with 4. This results in a highly negative change in entropy of transition state formation.Īs shown above, the Diels-Alder requires no acid nor base catalyst, meaning that a variety of non-extreme pH conditions are acceptable for the reaction. Kinetically, the Diels-Alder tends to proceed slowly, due to the exact position of the reactants required for transition state formation. Thermodynamically, this means that enthalpy drives the Diels-Alder reaction. However, the reaction also has a negative change in entropy, generally, because only one product forms from two reactants. Because sigma bonds are lower in energy than pi bonds, this means that the Diels-Alder reaction is exothermic. As we can see, the reaction nets two pi bonds broken and two sigma bonds formed. ![]()
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