On the possibility of conversion of strained bridgehead alkenes into carbenes via 1,2 hydrogen and 1,2 carbon migrations. A theoretical study of the rearrangements in the adamantene and protoadamantene systems

1998 ◽  
Vol 76 (6) ◽  
pp. 851-861 ◽  
Author(s):  
Gennady V Shustov ◽  
Michael TH Liu
Keyword(s):  
Experimental Data ◽  
Ab Initio ◽  
Theoretical Study ◽  
Activation Barrier ◽  
Main Channel ◽  
Diels Alder ◽  
Activation Barriers ◽  
Ab Initio Computation ◽  
Carbon Migration ◽  
High Level

Rearrangements of 2-adamantene 3, adamantylidene 4, and 4-protoadamantylidene 5 have been studied theoretically using high level ab initio computations. Adamantene 3 and adamantylidene 4 have singlet ground states. The conversion of 3 into 4 via 1,2 hydrogen migration ( Δ Gdouble dagger = 69.1 kcal mol-1) cannot compete with 1,2 carbon migration of 3 to 5 (30.3 kcal mol-1). The singlet carbene 5 rearranges to 2,4-dehydroadamantane 6 and 4,5-protoadamantene 9 via 1,3H and 1,2H shifts, respectively, with identical activation barriers of 8.8 kcal mol-1. The 1,2 migration of the bridge hydrogen in 5 leading to 3,4 protoadamantene 8 has a higher activation barrier (37.2 kcal mol-1). A retro Diels-Alder cycloaddition of 3 to 5-allyl-3-methylenecyclohex-1-ene 7 is the main channel of the unimolecular conversion of 3 ( Δ Gdouble dagger = 20.5 kcal mol-1). A predicted ratio of 7 > > 6 approx 9 of the products of thermolysis of 3 is in agreement with experimental data. The rearrangement of 4 into 6 via the 1,3H shift ( Δ Gdouble dagger = 11.8 kcal mol-1) dominates over the 1,2C shift of 4 to 8 (13.5 kcal mol-1), also in accord with experiment.Key words: adamantene, protoadamantenes, carbenes, rearrangements, ab initio, computation.

Electronic factors influencing the activation barrier of the Diels-Alder reaction. An ab initio study

1989 ◽  
Vol 54 (12) ◽  
pp. 2931-2935 ◽  
Author(s):  
Robert D. Bach ◽  
Joseph J. W. McDouall ◽  
H. Bernhard Schlegel ◽  
Gregory J. Wolber
Keyword(s):  
Ab Initio ◽  
Activation Barrier ◽  
Alder Reaction ◽  
Diels Alder ◽  
Ab Initio Study ◽  
Diels Alder Reaction ◽  
Factors Influencing

Facile formation of azines from reactions of singlet methylene and dimethylcarbene with precursor diazirines: theoretical explorations

1999 ◽  
Vol 77 (5-6) ◽  
pp. 540-549 ◽  
Author(s):  
Gennady V Shustov ◽  
Michael TH Liu ◽  
K N Houk
Keyword(s):  
Density Functional Theory ◽  
Ab Initio ◽  
Ring Opening ◽  
Density Functional ◽  
Activation Barrier ◽  
Thermal Reaction ◽  
Orbital Theory ◽  
Functional Theory ◽  
Activation Barriers ◽  
Singlet Methylene

The reactions of the singlet methylene (1a) and dimethylcarbene (1b), with their diazirine precursors, diazirine (2a), and dimethyldiazirine (2b), have been studied theoretically using ab initio and density functional theory. The reaction has no activation barriers for the parent system (1a + 2a) and proceeds via a reactive complex and a transition state with a small negative enthalpy of activation Δ Hnot =298 = -1.1 kcal mol-1, ΔSnot =298 = -34.4 cal mol-1 K-1, ΔG°298 = 9.2 kcal mol-1) for the dimethyl derivatives (1b + 2b). The formation of N-methylene diazirinium ylides (3a,b) is exothermic by 64-80 kcal mol-1. The isomer, 1,3-diazabicyclo[1.1.0]butane (4a), is more stable (5-12 kcal mol-1) than isomer 3a, but can neither be formed by direct thermal reaction of 1a with 2a nor undergo the direct rearrangement into formaldazine (5a). The rearrangement of ylides 3a,b into azines 5a,b proceeds by conrotatory C3-N1 ring opening. The predicted activation barrier of ca. 15 kcal mol-1 for the ring opening in ylide 3b is in excellent agreement with experimental data. The formation of pyridinium ylides from carbenes and pyridine is also studied.Key words: diazirinium ylide, ab initio MO (molecular orbital) theory, density functional theory, pyridinium ylide, CIS (singles configuration interaction) transition energies.

Understanding Metal-Free Catalytic Hydrogenation: A Systematic Theoretical Study of the Hydrogenation of Ethene

2004 ◽  
Vol 57 (7) ◽  
pp. 659 ◽  
Author(s):  
Bun Chan ◽  
Leo Radom
Keyword(s):  
Catalytic Activity ◽  
Ab Initio ◽  
Proton Affinity ◽  
Molecular Orbital ◽  
Catalytic Hydrogenation ◽  
Theoretical Study ◽  
Molecular Orbital Theory ◽  
Orbital Theory ◽  
Metal Free ◽  
High Level

Metal-free catalytic hydrogenation of ethene has been examined using high-level [G3(MP2)-RAD] ab initio molecular orbital theory. The dependence of the catalytic activity on the nature of the catalyst Z–X–H has been explored. We find that the catalytic activity is generally greater as Z–X–H becomes more acidic, both for first- and second-row atoms X. Molecules in which X is a second-row atom generally lead to more effective catalysis than the corresponding first-row analogues. The proton affinity at X of Z–X–H also contributes significantly to the catalysis in some cases (e.g. amines).

Étude DFT des réactions de cycloaddition de type Diels–Alder sur le 4-aza-6-nitrobenzofuroxane

2007 ◽  
Vol 85 (5) ◽  
pp. 331-335 ◽  
Author(s):  
Sameh Ayadi ◽  
Manef Abderrabba
Keyword(s):  
Theoretical Study ◽  
Dft Method ◽  
Diels Alder ◽  
Point Of View ◽  
Activation Barriers ◽  
Inverse Electron Demand ◽  
Electron Demand

The purpose of this work is a theoretical study of Diels–Alder reactions between the 4-aza-6-nitrobenzofuroxan 1 with a series of dienophiles 3a–3c. From a thermodynamic and orbital point of view, we discuss the reactivity and the stereoselectivty of these reactions. Activation barriers in the Diels-Alder reactions of compound 1 with a series of dienophiles 3a–3c have been calculated and discussed.Key words: inverse electron demand Diels–Alder (IEDDA), DFT method, 4-aza-6-nitrobenzofuroxane.

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