On the generation of oxirene and dimethyloxirene by retro-Diels–Alder reactions, and reactions of dimethyloxirene: a computational study

2002 ◽  
Vol 80 (1) ◽  
pp. 94-105 ◽  
Author(s):  
C Delamere ◽  
C Jakins ◽  
E Lewars
Keyword(s):  
Transition State ◽  
Ring Opening ◽  
Computational Study ◽  
Single Point ◽  
Diels Alder ◽  
Reaction Energy ◽  
One Step ◽  
Reaction Energies ◽  
Level 1 ◽  
Late Transition

The isomerization of oxirene (oxacyclopropene) (1) to ketene, dimethyloxirene (7) to dimethylketene via the oxo carbene ("ketocarbene"), and the retro-Diels–Alder extrusion of oxirene and dimethyloxirene from their formal adducts (9 and 24, respectively) with benzene were studied computationally. All species were optimized at the MP2(fc)/6–31G(df,p) level; the species involving 1 were also subjected to MP2(fc)/6–31G(df,p) frequency and single-point CCSD(T)/6–31G(df,p) calculations. At the CCSD(T)/6–31G(df,p)//MP2(fc)/6–31G(df,p) level 1 isomerized to ketene in one step with a barrier of 2.8 kJ mol–1 and a reaction energy of –320.6 kJ mol–1. The extrusion of 1 from 9 had a late transition state and activation and reaction energies of 264.2 and 214.2 kJ mol–1, respectively, cf. cyclopropene extrusion from its adduct (192.3 and 95.9 kJ mol–1), indicating an antiaromatic destabilization energy of 214.2 – 95.9 = 118 kJ mol–1 for 1. The carbene 8 from ring-opening of 7 lay 10.9 kJ mol–1 above 7 (CCSD(T)/6–31G(df,p)//MP2(fc)/6–31G(df,p)), but the transition state could not be found; 8 isomerized to dimethylketene (252.7 kJ mol–1 below 7) with a barrier of 16.4 kJ mol–1, and to s-(Z)- and s-(E)-butenone with barriers of 28.5 and 35.4 kJ mol–1, respectively. The UV (TDDFT, B3P86/6–311++G**//MP2(fc)/6–31G(df,p)) spectra of 1 and 7 were calculated. Discrepancies were seen between the calculated IR spectra of 7 (bis(trifluoromethyl)oxirene) and perfluoro ethyl methyloxirene, and those attributed to these species in earlier matrix-isolation work. Key words: oxirene, dimethyloxirene, ab initio, retro-Diels–Alder, Diels–Alder.

Exchange of Cl+ between Lone-Pair Donors and π-Donors: A Computational Study

2000 ◽  
Vol 6 (2) ◽  
pp. 153-160 ◽  
Author(s):  
Theis I. Sølling ◽  
Leo Radom
Keyword(s):  
Ab Initio ◽  
Computational Study ◽  
Lone Pair ◽  
Binding Energies ◽  
Lewis Base ◽  
Molecular Orbital Calculations ◽  
Reaction Energy ◽  
Lewis Bases ◽  
Donor Ability ◽  
Reaction Energies

The chemistry of mono-adducts ([Cl–X]+) between Cl+ and a Lewis base (X = NH3, H2O, HF, PH3, H2S or HCl) has been investigated using ab initio molecular orbital calculations at the G2 level. The reactions of such mono-adducts with additional Lewis bases (Y) are found to give [Y–Cl]+ plus X, generally without an intermediate barrier, via a bis-adduct [Y–Cl–X]+. The binding energies of the bis-adduct and the reaction energies are related to the donor properties of the Lewis bases. The reactions between the mono-adducts [Cl–X]+ and the π-donors ethylene and acetylene yield chloriranium and chlorirenium ions, respectively. These reactions proceed via complexes that resemble either the reactants or products depending on the sign of the reaction energy, the latter in turn being determined by the donor ability of the Lewis base. Results for the chlorine systems are compared with those for the corresponding phosphorus systems investigated previously.

Synthesis of bicyclic diones and thiones. Facile methylation of the enolates of bicyclo[2.2.1]heptane-2,5-dione and bicyclo[2.2.2]octane-2,5-dione. An AM1 computational study of bicyclic enolates

1992 ◽  
Vol 70 (3) ◽  
pp. 974-980 ◽  
Author(s):  
N. H. Werstiuk ◽  
S. Yeroushalmi ◽  
Hong Guan-Lin
Keyword(s):  
Raney Nickel ◽  
Good Yield ◽  
Computational Study ◽  
Alder Reaction ◽  
Diels Alder ◽  
Am1 Calculations ◽  
Diels Alder Reaction ◽  
Bicyclic Ketones ◽  
One Step

A group of bicyclic ketones and thiones have been synthesized for homenolization studies. Bicyclo[2.2.1]heptane-2,5-dione (6) undergoes unusually rapid tetramethylation giving 3,3,6,6-tetramethylbicyclo[2.2.1]heptane-2,5-dione (1) in good yield. Treatment of 1 with P2S5 in xylene gave 3,3,6,6-tetramethylbicyclo[2.2.1]heptane-2,5-dithione (2) and 3,3,6,6-tetramethyl 15-oxo-bicyclo[2.2.1]heptane-2-thione (3), which was converted into 4 with Raney nickel. Bicyclo[2,2,2]octane-2,5-dione (7), prepared via a Diels–Alder reaction between 2-trimethylsilyloxy-1,3-cyclohexadiene and and α-acetoxyacrylonitrile followed by a one-step desilylation/hydrolysis, also undergoes facile tetramethylation giving 3,3,6,6-tetramethylbicyclo[2.2.2]octane-2,5-dione (5) in good yield. AM1 calculations were carried out on the α-enolates of bicyclo[2.2.1]heptan-2-one, 6, 5-methylidenebicyclo[2.2.1]heptan-2-one, and 4-acetylbicyclo[2.2.1]-heptan-2-one in an attempt to gain information on the source of the enhanced acidity of the C-3 hydrogens of 6 and 7. Keywords: bicyclic ketones, thiones, synthesis.

scholarly journals A Density-Functional Study of the Conformational Preference of Acetylcholine in the Neutral Hydrolysis

Molecules ◽  
2020 ◽  
Vol 25 (3) ◽  
pp. 670 ◽  
Author(s):  
Rizka N. Fadilla ◽  
Febdian Rusydi ◽  
Nufida D. Aisyah ◽  
Vera Khoirunisa ◽  
Hermawan K. Dipojono ◽  
...  
Keyword(s):  
Transition State ◽  
Density Functional Calculations ◽  
Density Functional ◽  
Experimental Results ◽  
Functional Study ◽  
Conformational Preference ◽  
Reaction Energy ◽  
Density Functional Study ◽  
One Step ◽  
Experimental Findings

Acetylcholine, which is associated with Alzheimer’s disease, is widely known to have conformers. The preference of each conformer to undergo neutral hydrolysis is yet to be considered. In this study, we employed density-functional calculations to build the conformers and investigated their preference in one-step neutral hydrolysis. The results showed the preference in ten possible hydrolysis pathways involving seven acetylcholine conformers (reactant), four transition state structures, and two choline conformers (product). Three out of the seven acetylcholine conformers predicted from the results confirmed experimental findings on the conformers stability. We suggested that two out of ten possible pathways were observed in the experimental results based on agreement in reaction energy. Eventually, this study will emphasize the importance of considering acetylcholine conformers in its hydrolysis study.

scholarly journals Computational Study of Electronic Influence of Guanidine Substitution on Diels-Alder Reactions of Heterocyclic Dienes

2019 ◽  
Vol 92 (2) ◽  
pp. 279-286
Author(s):  
Ivana Antol ◽  
Luka Barešić ◽  
Zoran Glasovac ◽  
Davor Margetić
Keyword(s):  
Transition State ◽  
Quantum Chemical Calculations ◽  
Electronic Structures ◽  
Quantum Chemical ◽  
Computational Study ◽  
Cycloaddition Reaction ◽  
Diels Alder ◽  
Reaction Barriers ◽  
Reactivity Order

Quantum-chemical calculations of cycloaddition properties of cyclic heterodienes substituted with guanidine functionality were carried out. Molecular and electronic structures of series of dienes (pyrrole, furan, thiophene, isoindole and 1,3-butadiene) were calculated and reactivity order established on the basis of FMO theory. Transition state calculations of model [4+2] cycloaddition reaction with acetylene indicate that guanidine substitution influences reaction barriers in moderate extent (up to ~4 kcal mol–1). The substitution position plays an important role on the sign and magnitude of the effect and protonation of nitrogen possessing substituents increases reactivity of dienes.

Exo selectivity and the effect of disubstitution in the Diels–Alder reactions of butadiene with 3,3-disubstituted cyclopropenes

2004 ◽  
Vol 82 (11) ◽  
pp. 1589-1596 ◽  
Author(s):  
Tammy L Gosse ◽  
Raymond A Poirier
Keyword(s):  
Transition State ◽  
Density Functional ◽  
Computational Study ◽  
Alder Reaction ◽  
Diels Alder ◽  
Anomeric Effect ◽  
Isodesmic Reactions ◽  
Activation Barriers ◽  
Additional Stabilization ◽  
Transition State Structures

A density functional computational study was performed to accomplish two tasks: to examine the endo–exo selectivity in the Diels–Alder reactions of 3,3-disubstituted cyclopropenes with s-cis-butadiene, and to study the effect of disubstitution on the reactivity of the cyclopropene dienophile. Cyclopropene is substituted at C-3 with CH3, SiH3, NH2, PH2, OH, SH, F, and Cl; both 3-substituted and 3,3-disubstituted ground states are examined to determine relative reactivities. The exo transition-state structures are consistently lower in energy than the endo transition-state structures for the 3,3-disubstituted cyclopropene – butadiene system, and surprisingly, both modes of addition have lower activation barriers than the syn 3-substituted cyclopropene – butadiene system. Through a series of isodesmic reactions, we have concluded that there is an additional stabilization in the transition-state structures of the 3,3-disubstituted system that can account for the lowering of the activation barriers below that of the 3-substituted cases. This stabilization is a combination of the anomeric effect and the ring relaxation that occurs in the transition-state structure.Key words: Diels–Alder reaction, cyclopropene, exo selectivity, anomeric effect.

scholarly journals C-C and C-H bond cleavage reactions in acenaphthylene aromatic molecule, an ab-initio density functional theory study

2019 ◽  
Vol 10 (4) ◽  
pp. 403-408 ◽  
Author(s):  
Muthana Abduljabbar Shanshal ◽  
Qhatan Adnan Yusuf
Keyword(s):  
Transition State ◽  
Ab Initio ◽  
Ring Opening ◽  
Density Functional ◽  
Bond Cleavage ◽  
Dft Method ◽  
Functional Theory ◽  
Ring Opening Reaction ◽  
Reaction Energies ◽  
Cleavage Reactions

The ab-initio DFT method (B3LYP) is applied to the study of the C-C and C-H bond cleavage reactions in acenaphthylene molecule. It is found that the C-C bond cleavage proceeds via a singlet aromatic transition state, compelled through a disrotatoric ring opening reaction. A sigmatropic H atom shift follows the transition state in some of these reactions, where the formation of a methylene -CH2,acetylenyl-, allenyl- or butadienyl moiety in the final product is possible. The calculated activation and reaction energies for the C-C ring opening are 164-236 and 52-193 kcal/mol, respectively. The calculated cleavage reaction energies for the C-H bonds are 117-122 kcal/mol and the activation energies are 147-164 kcal/mol.

Tests for aromaticity applied to the pentalenoquinones — A computational study

2001 ◽  
Vol 79 (10) ◽  
pp. 1492-1504
Author(s):  
C Delamere ◽  
C Jakins ◽  
E Lewars
Keyword(s):  
Computational Study ◽  
Single Point ◽  
Resonance Energy ◽  
Dft Method ◽  
Diels Alder ◽  
Chemical Hardness ◽  
Bond Orders ◽  
Resonance Energies ◽  
Ring Opening Reactions ◽  
Nics Calculations

Criteria for aromaticity and antiaromaticity were applied to the four pentalenoquinones, 1,2-, 1,5-, 1,4-, and 1,6-pentalenoquinone, i.e., bicyclo[3.3.0]octa-4,6,8-triene-2,3-dione (7a), bicyclo[3.3.0]octa-3,5,8-triene-2,7-dione (7b), bicyclo[3.3.0]octa-1(5),3,7-triene-2,6-dione (7c), and bicyclo[3.3.0]octa-1(5),3,6-triene-2,8-dione (7d). Geometry optimizations and frequency calculations were done with the pBP/DN* DFT method as implemented in Spartan, and single-point HF/3-21G calculations to obtain Löwdin bond orders (Spartan), as well as HF/6-31G* NICS calculations (Gaussian 98) were also carried out. Geometries and bond orders, chemical hardness, and NICS values gave no definite indication of aromatic or antiaromatic character. However, homodesmotic ring-opening reactions to give acyclic analogues indicated that 7a and 7b are nonaromatic (resonance energies –11 and 5 kJ mol–1) while 7c and 7d are antiaromatic (resonance energies –83 and –54 kJ mol–1). The resonance energies were obtained with the aid of an estimate of the strain energy of the molecules 7 (86 kJ mol–1) by a novel extrapolation procedure on hydropentalenes. Calculated pBP/DN* activation energies for Diels–Alder reactions with ethyne and ethene placed 7a and 7b in an "unreactive" class similar to 1,3-butadiene and fulvene, and 7c and 7d in a "reactive" class, similar to cyclopentadienone.Key words: aromaticity, pentalenoquinones, DFT, hardness, NICS, homodesmotic, resonance energy, bicyclo[3.3.0]octatrienediones.

On the Conrotatory Ring Opening of 3-Carbomethoxycyclobutene Vis-À-Vis 3-Carbomethoxy-1,2-Benzocyclobutene and the Predominant Inward Opening of 3-Dimethylaminocarbonyl-1,2-Benzocyclobutene

2018 ◽  
Author(s):  
Veejendra Yadav ◽  
Dasari L V K Prasad ◽  
Arpita Yadav ◽  
Maddali L N Rao
Keyword(s):  
Transition State ◽  
Ring Opening ◽  
Electron Process ◽  
Ring Opening Reaction ◽  
Stable Species ◽  
Electron Event

<p>The torquoselectivity of conrotatory ring opening of 3-carbomethoxycyclobutene is controlled by p<sub>C1C2</sub>→s*<sub>C3C4</sub> and s<sub>C3C4</sub>→p*<sub>CO</sub> interactions in the transition state in a 4-electron process as opposed to only s<sub>C3C4</sub>→p*<sub>CO</sub> interaction in an apparently 8-electron event in 3-carbomethoxy-1,2-benzocyclobutene. The ring opening of 3-carbomethoxy-1,2-benzocyclobutene is sufficiently endothermic. We therefore argue that the reverse ring closing reaction is faster than the forward ring opening reaction and, thus, it establishes an equilibrium between the two and subsequently allows formation of the more stable species <i>via</i> outward ring opening reaction. Application of this argument to 3-dimethylaminocarbonyl-1,2-benzocyclobutene explains the predominantly observed inward opening.</p>

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