Gain or loss of aromaticity in Diels–Alder transition states and adducts: a theoretical investigation

Manoharan, Mariappan; Venuvanalingam, Ponnambalam

doi:10.1002/(sici)1099-1395(199802)11:2<133::aid-poc981>3.0.co;2-r

Cited by 22 publications

(14 citation statements)

References 59 publications

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“…Energy profile presented in Figure 4 and the data presented in Table 2 show that cycloreversion by CO 2 elimination is more facile than HCN elimination, kinetically and thermodynamically CO 2 elimination yields pyridine an aromatic product, and therefore more stable, while HCN elimination leads to the formation of 2P that is partially aromatic and obviously less stable. Thus gain in aromaticityin CO 2 elimination pathway reduces the activation energy greatly as reported [29]. It is noted that barrier to cycloreversion of Al (11.97 kcal.mol -1 ) and A2 (14.52 kcal.mol -1 ) is rather much lower and the reaction is also thermodynamically favoured to a greater extent.…”

Section: A Energetics and Foe Analysissupporting

confidence: 53%

Tandem Cycloaddition-Cycloreversion of 2-pyrone and 1,4-oxazinone with Acetylene - A DFT Insight

Kalpana¹,

Akilandeswari²,

Venuvanalingam³

2021

IJPC

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Reaction of either 2-pyrone or 1,4-oxazinone with acetylene follows the sequence of cycloadditioncycloreversion through concerted mechanism. Transition states for both cycloaddition and cycloreversion pathways have been obtained in both the cases by modelling the reactions at B3LYP/6-31g (d) level. Cycloreversion is faster than cycloaddition in the case of 2-pyrone due to the enhancement of aromaticity resulting the product as benzene. In contrast, oxazinone has rapid cycloaddition. It is ascribed to the presence of nitrogen in this system. Removal of either CO 2 or HCN is plausible in this mechanism to complete the reaction. Even though two pathways are feasible for cycloreversion, CO 2 extrusion is more preferable than HCN elimination. In these two studied molecules, there is an enhancement of aromaticity up to transition states like any other pericyclic reaction and further it diminishes during cycloaddition. Further, aromaticity is specifically augmented in cycloreversion phase during CO 2 elimination resulting to yield pyridine whereas competitive HCN elimination results in the formation of 2-pyrone which is less facile. In both the molecules the aromatic enhancement of the cycloreversion is substantiated through the study of magnetic susceptibility of the ring fragment along the reaction coordinate. Further the study also reveals the effect of halogen substituted at different carbons of 2-pyrone ring.

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Section: A Energetics and Foe Analysissupporting

confidence: 53%

Tandem Cycloaddition-Cycloreversion of 2-pyrone and 1,4-oxazinone with Acetylene - A DFT Insight

Kalpana¹,

Akilandeswari²,

Venuvanalingam³

2021

IJPC

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“…48 Reaction of maleic anhydride ͑dienophile͒ with anthracene can be achieved with up to 90% yield, 49 and the ethylene+ anthracene DA reaction energy has been estimated to be Ϫ20.4 kcal/mol using DFT. 50 The synthesis of anthracene DA dimers have not been reported, however, nor have they been studied with quantum chemical methods.…”

Section: A Singlet Dimersmentioning

confidence: 99%

A quantum chemistry study of Diels–Alder dimerizations in benzene and anthracene

Quenneville

Germann

2009

The Journal of Chemical Physics

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There is considerable experimental evidence of covalent dimerization of aromatic compounds occurring under shock conditions. Because of their endothermicity, these reactions could play a large role in the shock initiation process of aromatic molecular explosives such as 2,4,6-trinitrotoluene and 1,3,5-triamino-2,4,6-trinitrobenzene by withdrawing energy from the shock compression. Very little is known about the energetics, however, and this knowledge is crucial for the design of empirical force fields that can treat shock-induced chemistry. We have employed ab initio electronic structure and density functional methods to study the Diels-Alder (DA) dimerizations of benzene and anthracene. The enthalpy of reaction for DA benzene dimerization is predicted to be +35.9 kcal/mol. The stepwise pathway to this dimer involves formation of a stable triplet intermediate that requires 71.8 kcal/mol of energy. Transition states along both the concerted and stepwise pathways were optimized and the energetics of the reaction pathways are detailed. The former is found to be the energetically preferred mechanism. Nine DA dimers of anthracene were found, with six predicted to have dimerization DeltaH(rxn)'s of 24-55 kcal/mol, two with dimerization energies near zero and one that is formed through an exothermic reaction. Twelve triplet dimers of anthracene, with DeltaH(rxn)'s ranging from 33-50 kcal/mol, are also described. Finally, the potential importance of these reactions in the context of shock compression of these materials is discussed.

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“…25 The reactions between various dienophiles and anthracene, which may be considered as a benzo-annelated diene, are well known in the literature. 2b,20,26, 27 Benzo-fused thiophenes are known for their applications in the pharmaceutical industry. 8c The Diels-Alder strategy has been used in innovative ways to construct novel polycyclic cages using furan and its derivatives as dienes.…”

Section: Introductionmentioning

confidence: 99%

DFT study on the cycloaddition reactions of [c]-annelated carbo- and heterocyclic five-membered dienes with ethyleneElectronic supplementary information (ESI) available: figures and tables of the principal geometric parameters of all the dienes, transition states and products obtained at the B3LYP/6-31G* level and the Cartesian coordinates of all the optimized structures considered in this study. See http://www.rsc.org/suppdata/p2/b2/b205663a/

Dinadayalane

Sastry

2002

J. Chem. Soc., Perkin Trans. 2

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B3LYP/6-31G* calculations were done on a series of [c]-annelated heterocyclic five-membered dienes and their cycloaddition transition state structures and products. Cyclobutano[c]-, cyclobuteno[c]-and benzo[c]-fused fivemembered rings represent non-aromatic, antiaromatic and aromatic ring fused dienes, respectively, and their reactivity was studied with ethylene as dienophile. In the cases of cyclobutano-and cyclobuteno-fused dienes, the fused portion remains a mere spectator and no significant geometric variations are seen along the reaction coordinate. In contrast, in the benzo-fused systems, the fused benzene ring witnesses significant changes in the bond lengths along the reaction coordinate highlighting the active participation of the π-framework in the reaction. Thus, this may be classified as an [8 ϩ 2] cycloaddition. The benzo[c]-fused rings exhibit the lowest activation energies followed by cyclobutano and cyclobuteno analogues, and the exothermicities decrease in the same order. A linear relationship between the reaction exothermicity and activation energy is obtained for the systems under consideration. The percentage bond length alternation on going from reactant to transition state, the Fukui function indices and frontier orbital analysis, extent of charge transfer from diene to dienophile at the transition state, and deformation energies were estimated to explain the reactivity of the dienes with ethylene.

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Gain or loss of aromaticity in Diels–Alder transition states and adducts: a theoretical investigation

Cited by 22 publications

References 59 publications

Tandem Cycloaddition-Cycloreversion of 2-pyrone and 1,4-oxazinone with Acetylene - A DFT Insight

Tandem Cycloaddition-Cycloreversion of 2-pyrone and 1,4-oxazinone with Acetylene - A DFT Insight

A quantum chemistry study of Diels–Alder dimerizations in benzene and anthracene

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