Substituent effects on strain energies

Dill, James D.; Greenberg, Arthur; Liebman, Joel F.

doi:10.1021/ja00517a005

Cited by 160 publications

(73 citation statements)

References 21 publications

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“…Also it was found that CT substituent is highly stabilizing as compared to radical and cation, probably because the O" substituent is a relatively strong a and n donor [56], which causes the cyclopropenyl anion to obtain aromatic character (6 n electrons), as compared to the radical (5 n electrons) and the cation (4 n electrons). For the electron withdrawing substituents such as CHO, CN and N0 2 , the stabilizing effect is more pronounced in the case of anion than in that of both radical and cation.…”

Section: Stabilization By Substituentsmentioning

confidence: 99%

A Theoretical Study of Monosubstituted Cyclopropenyl System

Yahya

Khalil

1992

Zeitschrift Für Naturforschung A

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MONDO-Forces calculations have been performed, with complete optimization of geometry on X-cyclopropenyl system (cations, radicals and anions), where X is H, O", OH, CH 3 , CN, N0 2 , F and CF 3 . All substituents prefer planar structure when substituted on both cations and radicals, while they prefer pyramidal structure in the case of anions except CF 3 . The substituents O", OH and F act as electron releasing, while CHO, N0 2 and CF 3 act as electron withdrawing when substituted on cyclopropenyl system. CH 3 and CN show amphielectronic behaviour. They act as electron releasing on the cations and withdrawing on both radicals and anions depending on electron demand. In the case of cations and radicals, all substituents were found to increase the vicinal bonds and decrease the distal bonds and bond angles to which the substituent is attached. For anions the substitutents show no such regularity because the substituents are out of the three-membered ring plane. All substituents increase the stability of the cyclopropenyl system except CF 3 in the case of the cation.The cyclopropenyl cation is the smallest aromatic molecule which has two ^-electrons and satisfies the Hückel 4 n + 2 rule. The electronic structure is of great interset since the molecule is highly strained but despite of this the ion is stable in the form of salts, e. g. C 3 H 3 • SbCl^, and also in polar solvents [1]. D 3h configuration of the ion is indicated by its IR and NMR spectra [1], Allen has reported a structural analysis for two cyclopropenyl cation derivatives based upon Xray crystallographic data [2]. Clark carried out ab initio LCAO SCF MO Calculations on both C 3 H 3 + and C3H3 and discussed the aromaticitiy and antiaromaticity [3]. Ha et al. reported an ab initio LCAO SCF MO investigation on C 3 H 3 + , C 3 Hj and C 3 H 3~ and discussed the geometry and stability of these species [4j. Random et al. aiso carried out ab initio calculations on C3H3 using STO-3G and 6-31G and obtained the equilibrium structure of the ion [5]. Takada and Ohno also published an ab initio CI calculation on the electronic structure of C3H3 [6]. The most recent ab initio calculations on the molecular structure and vibrational spectrum of C3H3 were performed by Xie et al. [7], and Lee et al. [8], Cyclopropenyl free radical, the simplest member of the series of fully conjugated cyclic radicals, has been the subject of experimental [9-13] and theoretical studies [4,[14][15][16][17][18][19][20],The theoretical work by Chipman and Miller [20] predicts an ethylenic structure of C s symmetry as the lowest energy form. The hydrogen atom at the apex of the isoceles triangle is bent substantially out of the ring plane. The allylic structure, which satisfies the Jahn-Teller theorem, is predicted to be 5 kcal/mole higher in energy. Experimental work by Closs and Redwine [13] support the C s structure and rules out the allylic structure. There is no experimental information on the properties of the neutral radical, so it is necessary to resort to theoretical studies.The cyc...

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Section: Stabilization By Substituentsmentioning

confidence: 99%

A Theoretical Study of Monosubstituted Cyclopropenyl System

Yahya

Khalil

1992

Zeitschrift Für Naturforschung A

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“…They characterized the microwave and infrared spectra of VA and EI two isomers, E-and Z-ethyleneimine in a temperature range from 150 to 900 °C and suggested a non-planar structure of vinylamine (CH 2 =CHNH 2 ) [1,2]. Moreover, theoretical studies on VA structure produced the same result [16,18,20,[56][57][58][59][60]. Traeger et.…”

Section: Introductionmentioning

confidence: 88%

Computational study for the second-stage cracking of the pyrolysis of ethylamine: Decomposition of methanimine, ethenamine, and ethanimine

Almatarneh

Barhoumi

Al-Tayyem

et al. 2016

Computational and Theoretical Chemistry

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Accepted ManuscriptThis is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractThe mechanism that accounts for the observed experimental activation energy for the decomposition of ethylamine (EA) is still unknown. This paper reports the first detailed study of possible mechanisms for the pyrolysis of second-stage cracking product of ethylamine: the decomposition reaction of methanimine, ethanimine, and aminoethylene. Investigated reactions charactarise either H 2 elimination or 1,3-proton shift. These pathways result in the removal of H 2 , CH 4 , and NH 3 ; and the formation of hydrogen cyanide, acetylene, acetonitrile, ethynamine, and ketenimine. The IRC analysis was carried out for all transition state structures to obtain the complete reaction pathways. The stationary points were fully optimized at B3LYP and MP2 levels of theory using the 6-31G(d), 6-31G(2df,p), and 6-31++G(3df,3dp) basis sets. Based on comparing energetic requirements, we find 1,3-proton shift is the most probable pathway for the decomposition of ethanimine. The decomposition reaction of ethenamine was the most plausible reaction with an activation energy of 297 kJ mol −1 calculated at the composite method of G4MP2.

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“…Methylene is a ground state triplet (la), lying -10 kcal/mol below the singlet state (lb) (28). If the substituent X is a m--donor then, as in carbocations, the singlet structure is stabilised by donation into the "vacant" p-orbital on the carbene carbon.…”

Section: (B) Carbenesmentioning

confidence: 99%

“…T-Donating substituents are weakly stabilising in ethylene (28) but are strongly stabilising in a-X-ethyl cations (6), with the result that the proton affinities of alkenes H2C=CHX are larger for T-donors and are very substituent dependent (Table 4). The cyano group is weakly stabilising in acrylonitrile, HZC=CH(CN) (28), and is destabilising in CH7CH(CN)+ (6) and consequently the proton affinity of acrylonitrile is 18.2 kcal/mol less than that of ethylene. By comparison, in the protonation of singlet carbenes, both CHX and CH,Xi are strongly stabilised by T-donors and the proton affinities of the carbenes are therefore less substituent dependent than those of the ethylenes.…”

Section: (C) Proton Affinities Of Singlet Carbenesmentioning

confidence: 99%

Substituent effects in carbocations CX⁺, CHX^+•, and CH₂X⁺, and in singlet and triplet carbenes CHX. Proton affinities of singlet carbenes

Hopkinson¹,

Lien²

1985

Can. J. Chem.

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Abinitio molecular orbital calculations with a 6-31G* basis set have been used to optimise structures for CX+, CHX+•, CHX (both singlets and triplets), H2CX+ and H3CX (X = H, CH3, NH2, OH, F, CN, and NC). Single point calculations were then performed on the 6-31G* optimised structures using a configuration interaction method involving all single and double excitations from the valence shell. Stabilisation energies for the carbocations are compared with those already reported for H2CX+. For the carbenes the single-triplet energy gap is examined as a function of substituent and the stabilisation energies of the singlet carbenes are compared with those of the isoelectronic carbocations H2CX+. Proton affinities are reported for the singlet carbenes and are compared with the proton affinities of similarly substituted ethylenes, H2C=CHX.

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Substituent effects on strain energies

Cited by 160 publications

References 21 publications

A Theoretical Study of Monosubstituted Cyclopropenyl System

A Theoretical Study of Monosubstituted Cyclopropenyl System

Computational study for the second-stage cracking of the pyrolysis of ethylamine: Decomposition of methanimine, ethenamine, and ethanimine

Substituent effects in carbocations CX⁺, CHX^+•, and CH₂X⁺, and in singlet and triplet carbenes CHX. Proton affinities of singlet carbenes

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Substituent effects on strain energies

Cited by 160 publications

References 21 publications

A Theoretical Study of Monosubstituted Cyclopropenyl System

A Theoretical Study of Monosubstituted Cyclopropenyl System

Computational study for the second-stage cracking of the pyrolysis of ethylamine: Decomposition of methanimine, ethenamine, and ethanimine

Substituent effects in carbocations CX+, CHX+•, and CH2X+, and in singlet and triplet carbenes CHX. Proton affinities of singlet carbenes

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Substituent effects in carbocations CX⁺, CHX^+•, and CH₂X⁺, and in singlet and triplet carbenes CHX. Proton affinities of singlet carbenes