The torsional energy levels of ethylene: A re-evaluation

Wallace, R.

doi:10.1016/s0009-2614(89)87449-4

Cited by 31 publications

(15 citation statements)

References 8 publications

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“…Interestingly, a good estimate of the C=C bond rotational barrier of ethylene in S 0 is obtained when its optimal C=C bond length [1.326 with M06-2X/6-311 + + GA C H T U N G T R E N N U N G (d,p)] is used in the exponential expression derived through the fit of Figure S2 (61.2 kcal mol À1 for our estimated barrier versus 59.7-64.5 kcal mol À1 for the barrier height as earlier deduced from experiments and high-level calculations). [52][53][54][55][56][57][58][59] From the point of view of applications, it would be useful if the shape of the T 1 PES of a new but not yet synthesized olefin could be predicted from a calculated ground-state property prior to synthesis and photochemical experimentation. Indeed, for set A olefins we found a relationship between DE(T 1 ) and the degree of (anti)aromaticity at the planar S 0 olefin, as given by NICSA C H T U N G T R E N N U N G (S 0 ;1) zz (r 2 = 0.916 and 0.993 for linear and sigmoidal fits, respectively; Figure 4).…”

Section: Resultsmentioning

confidence: 99%

Aromaticity Effects on the Profiles of the Lowest Triplet‐State Potential‐Energy Surfaces for Rotation about the CC Bonds of Olefins with Five‐Membered Ring Substituents: An Example of the Impact of Baird’s Rule

Zhu

Fogarty

Möllerstedt

et al. 2013

Chemistry A European J

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A density functional theory study on olefins with five-membered monocyclic 4n and 4n+2 π-electron substituents (C4H3X; X=CH(+), SiH(+), BH, AlH, CH2, SiH2, O, S, NH, and CH(-)) was performed to assess the connection between the degree of substituent (anti)aromaticity and the profile of the lowest triplet-state (T1) potential-energy surface (PES) for twisting about olefinic C=C bonds. It exploited both Hückel's rule on aromaticity in the closed-shell singlet ground state (S0) and Baird's rule on aromaticity in the lowest ππ* excited triplet state. The compounds CH2=CH(C4H3X) were categorized as set A and set B olefins depending on which carbon atom (C2 or C3) of the C4H3X ring is bonded to the olefin. The degree of substituent (anti)aromaticity goes from strongly S0 -antiaromatic/T1 -aromatic (C5H4 (+)) to strongly S0 -aromatic/T1- antiaromatic (C5H4(-)). Our hypothesis is that the shapes of the T1 PESs, as given by the energy differences between planar and perpendicularly twisted olefin structures in T1 [ΔE(T1)], smoothly follow the changes in substituent (anti)aromaticity. Indeed, correlations between ΔE(T1) and the (anti)aromaticity changes of the C4 H3 X groups, as measured by the zz-tensor component of the nucleus-independent chemical shift ΔNICS(T1;1)zz , are found both for sets A and B separately (linear fits; r(2) =0.949 and 0.851, respectively) and for the two sets combined (linear fit; r(2) =0.851). For sets A and B combined, strong correlations are also found between ΔE(T1) and the degree of S0 (anti)aromaticity as determined by NICS(S0,1)zz (sigmoidal fit; r(2) =0.963), as well as between the T1 energies of the planar olefins and NICS(S0,1)zz (linear fit; r(2) =0.939). Thus, careful tuning of substituent (anti)aromaticity allows for design of small olefins with T1 PESs suitable for adiabatic Z/E photoisomerization.

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Section: Resultsmentioning

confidence: 99%

Aromaticity Effects on the Profiles of the Lowest Triplet‐State Potential‐Energy Surfaces for Rotation about the CC Bonds of Olefins with Five‐Membered Ring Substituents: An Example of the Impact of Baird’s Rule

Zhu

Fogarty

Möllerstedt

et al. 2013

Chemistry A European J

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“…Δ E R represents the energy required for decoupling the three electron pairs associated with the Zn−C bond, the C−Cl bond, and the olefin π bond (addition) or, alternatively, the C−H σ bond (insertion) and can be evaluated to a good approximation from the energies of these breaking bonds. Since the contribution to Δ E R arising from the ClCH 2 ZnCl fragment is the same for the two reactions, the variation of Δ E R on going from addition (Δ E R (a) ) to insertion (Δ E R (i) ) is determined by the difference between the energy of the olefin π bond and that of a vinylic C−H bond: since the former (about 60 kcal mol -1 ) is much smaller than the latter (about 108 kcal mol -1 ), Δ E R (i) is larger than Δ E R (a) . In a similar way we can evaluate the relative magnitude of Δ E P (a) and Δ E P (i) , which represent the energy required for decoupling the electron-pair of the Zn−Cl bond in ZnCl 2 and the two electron-pairs of the two new C−C bonds in cyclopropane (addition) or the two new C−C and C−H bonds in propene (insertion).…”

Section: Resultsmentioning

confidence: 99%

A DFT Study of the Simmons−Smith Cyclopropanation Reaction

1997

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In this paper we have used a DFT (B3LYP) approach to investigate the potential energy surface for the reaction between ethylene and (chloromethyl)zinc chloride (ClCH2ZnCl), which represent a model system for the Simmons−Smith cyclopropanation reaction. Two reaction channels have been found: one leads to the cyclopropane product (addition channel) and the other to the propene product (insertion channel). The addition reaction has an activation energy of 24.7 kcal mol-1 and, as experimentally found, is favored with respect to the insertion, which is characterized by a larger activation energy (36.0 kcal mol-1). The addition transition state corresponds to a three-centered structure which explains the stereochemical features which have been experimentally observed for this reaction. A simple diabatic model is used to rationalize the reactivity pattern that characterizes the Simmons−Smith cyclopropanation and the different behavior observed for the reaction between singlet methylene 1CH2 and olefins.

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“…The rotational barrier in ethylene computed using the same basis set and a similar GVB method is 69.6 kcal/mol, which is 9.6 kcal/mol too large. 15…”

Section: Resultsmentioning

confidence: 99%

The beryllium-carbon double bond: bonding in CH2Be(CO)n (n = 1, 2)

Sunil¹

1993

J. Phys. Chem.

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The results of theoretical studies on the structure, stability, and properties of CHzBeCO and CH2Be(C0)2 are discussed. It is shown that the Be to methylene carbon bond is a double bond in both molecules. In CHIBe(C0)2 the properties of the Be-C(CH2) double bond are as follows: bond length of 1.592 & bond energy of 99.6 kcal/mol, stretching frequency of 1174 cm-*, and a rotational barrier of 57.9 kcal/mol. The properties of the BeC(CH2) bond in CHzBeCO are similar to those in CH2Be(C0)2. The binding energies of the first and second CO in CHzBe(C0)z are 36.4 and 25.6 kcal/mol, respectively.Recently, it was shown that Be(C0)Z is a bent molecule with a triplet ground state,lJ and its electronic structure is analogous to the 3B1 ground state of methylene. Thevalidity of this analogy was tested by quantum chemical studies of the structure, stability, and properties of Be2(C0)4 and Be3(C0)6. The results of these studies show that Be2(C0)4, an ethylene analogue, is an exceptionally stable molecule with a double bond between Be atoms2 and that BeS(C0)6 is also a strongly bound molecule with a geometrical structure analogous to cy~lopropane.~ These results led to the question of whether Be(C0)2 can interact with CH2 to form CH2Be(C0)2, a molecule with a B e C double bond. This possibility was studied by ab initio quantum chemical studies of CH2BeC0 and CH2Be(C0)2, the results of which are described below. This is not the first attempt to study the possible stability of a molecule with a B e C double bond. The molecule CH2Be which formally contains a Be-C double bond has been studied by Lamanna and Maestro? Pople, Schleyer, and co-w~rkers,~.~ and Sana and Leroy.' All the studies of this molecule agree that the ground state is a strongly bound 3B1 state. In this paper, the properties of the methylene carbon to Be bond in CHzBeCO and CH2Be(CO)z are compared with that in CH2Be. MethodThe spin-restricted HartreeFock (HF) self-consistent-field wave function was used to describe the closed-shell systems and the spin-unrestricted wave functions for the open-shell systems. The geometries were optimized at both the HF and second-order perturbation theory (MP2) level of approximations using the 6-3 1G*(5d) basis sets for all the molecules. Harmonicvibrational frequencies were computed at both levels of theory to determine the natureof the stationary points on the potential energy surfaces.The electron correlation energies were computed for both the HF and MP2 optimized geometries through complete fourthorder Moller-Plesset perturbation theory? and second-, third-, and fourth-order energies are denoted MP2, MP3, and MP4, respectively. In addition, the quadratic configuration interaction theory10 including the effects of triple excitations (QCISD(T)) was also employed in determining the electron correlation energies. The electron correlation energy computations included only the valence electrons. All the computations were carried out using the Gaussian 90 program." Results and DiscussionThe geometries of the ground and lowest excited...

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The torsional energy levels of ethylene: A re-evaluation

Cited by 31 publications

References 8 publications

Aromaticity Effects on the Profiles of the Lowest Triplet‐State Potential‐Energy Surfaces for Rotation about the CC Bonds of Olefins with Five‐Membered Ring Substituents: An Example of the Impact of Baird’s Rule

Aromaticity Effects on the Profiles of the Lowest Triplet‐State Potential‐Energy Surfaces for Rotation about the CC Bonds of Olefins with Five‐Membered Ring Substituents: An Example of the Impact of Baird’s Rule

A DFT Study of the Simmons−Smith Cyclopropanation Reaction

The beryllium-carbon double bond: bonding in CH2Be(CO)n (n = 1, 2)

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