Microwave spectrum and<i>ab initio</i>calculations of ethylbenzene: potential energy surface of the ethyl group torsion

Camináti, Walther; Damiani, D.; Corbelli, G.; Velino, Biagio; Bock, Charles W.

doi:10.1080/00268979100102661

Cited by 63 publications

(32 citation statements)

References 17 publications

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“…Supersonic molecular, jet laser spectroscopy (5) and low- (6) and high- ' 3 3 H (7) resolution microwave spectra for the vapor show that 4 is the conformation of lowest energy; the latter spectra 5 6 (7) are consistent with an internal barrier ranging from 4.9 to 7.8 kJ/mol, in rough agreement with various (7,8) ab itzitio molecular orbital computations at the Hartree-Fock or post-Hartree-Fock level of theory, as well as with heat capacity data (9). In solution (8), the long-range coupling constant over six bonds between the methylene and para ring protons suggests that the conformational behaviour of ethylbenzene is the same in various solvents and that, if the barrier is purely twofold, its magnitude is 5.3, 2 0.3, kJ/mol.…”

Section: Introductionsupporting

confidence: 59%

The conformational behavior of isobutylbenzene in CS₂/C₆D₁₂ solution at 300 K

Schaefer¹,

Lee²

1992

Can. J. Chem.

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The 1H nuclear magnetic resonance spectrum of isobutylbenzene as a dilute solution in CS2/C6D12 at 300 K is analyzed. The gauche conformer (statistical weight 2) predominates, as was previously shown for a jet-cooled stream of this compound. The apparent twofold barrier to rotation about the Csp2—Csp3 bond is 10.5 ± 0.5 kJ/mol, as must be the case for the analogous gauche conformer of n-propylbenzene. The internal barriers are compared for ethylbenzene, gauche isobutylbenzene, and neopentylbenzene. AM1 and STO-3G MO computations of the conformer stabilities and barriers are reported, the latter being in better agreement with experiment.

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Section: Introductionsupporting

confidence: 59%

The conformational behavior of isobutylbenzene in CS₂/C₆D₁₂ solution at 300 K

Schaefer¹,

Lee²

1992

Can. J. Chem.

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“…Computations at various levels of ab initio molecular orbital theory (1,2) agree that 1 and 2 represent the conformers of lowest and highest energy, respectively, but predict the presence of a minor fourfold, in addition to the major twofold, component of the internal rotational potential. For example, if a theoretical fourfold component of 0.9 kJ/mol is used to fit the rotational spectrum in the vapor phase (2), then the twofold component is 4.9 + 0.7 kJ/mol; alternatively, the latter is 7.8 + 0.7 kJ/mol if the former vanishes.…”

Section: Introductionmentioning

confidence: 99%

“…For example, if a theoretical fourfold component of 0.9 kJ/mol is used to fit the rotational spectrum in the vapor phase (2), then the twofold component is 4.9 + 0.7 kJ/mol; alternatively, the latter is 7.8 + 0.7 kJ/mol if the former vanishes. A combined molecular mechanicsmolecular orbital method (3) arrives at 4.2 kJ/mol for the energy difference between 1 and 2.…”

Section: Introductionmentioning

confidence: 99%

Concerning the internal rotational barrier and the experimental and theoretical ⁿJ(¹³C,¹³C) and ⁿJ (¹H,¹³C) in ethylbenzene-β-¹³C

Schaefer¹,

Chan²,

Sebastian³

et al. 1994

Can. J. Chem.

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The 1H nuclear magnetic resonance spectra of ethylbenzene-β-13C in CS2/C6D12 and acetone-d6 solutions yield long-range 1H,1H and 1H,13C coupling constants. The 13C {1H} NMR spectra yield 13C, 13C couplings. The conformational dependence of some of these coupling constants is compatible with two values of the barrier to internal rotation about the exocyclic Csp2—Csp3 bond. If the fourfold component of the internal rotational potential is not larger than about 20% of the twofold component and the perpendicular conformer is most stable, then the barrier height is probably less than 6 kJ/mol. However, if the stable conformer has a torsion angle of 60° for the exocyclic C—C bond, then the coupling constants are consistent with a twofold barrier of about 23 kJ/mol. Experimental values of [Formula: see text] and [Formula: see text], where ψ and θ are the torsion angles for the exocyclic C—C and C—H bonds, respectively, are compared to those obtained from INDO MO FPT computations of the angular dependence of nJ(H,C), and nJ(H,H), nJ(C,C) for n ≥ 3. For example, the computations very likely give the correct qualitative ψ dependence of 5J(C,C), yet overestimate its extremum by about a factor of two, either because of an overestimate of the σ–π exchange integrals or because of too large a valence orbital density at the carbon nucleus. Other nJ values are discussed in a similar manner and, because optimized geometries are used in the computations, a somewhat more reliable treatment arises for some coupling constants; an example is 3J(C,C) at small torsion angles.

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“…[6 ll] has produced results which are in accord with other evidence for the distribution function PLc(O), or which are close to the predictions of MO theory for an isolated molecule.An alternative method for obtaining PLC(O) overcomes the dependence on order by writing the mean potential as[12] U(~, ~), ~r = Uext(}~, ~2, 1/1) -~-Uint(~/). (7)The additiona!…”

mentioning

confidence: 99%

An investigation of the conformation of 4-chloroethylbenzene as a solute in a nematic liquid crystalline solvent

Celebre

Longeri

et al. 1995

Molecular Physics

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The conformation of the ethyl group relative to the phenyl ring plane in 4-chloroethylbenzene has been investigated by recording and analysing the proton NMR spectrum of a sample dissolved in a nematic liquid crystalline solvent. The dipolar couplings obtained are compared with values calculated by the additive potential (AP) and maximum entropy (ME) molecular mean field theoretical models. In both cases good agreement between observed and calculated couplings could be obtained only by adopting a model for rotation about the ring C bond which allows for geometry relaxation. The ME method produces a conformational distribution with an absolute maximum at 90 ~ and a secondary maximum at 0, which is also the shape found to give the best fit to the data by the AP method. However, constraining the shape of the conformational distribution to that found by the molecular orbital calculations and using the AP method yields an acceptable, if not the best, fit to the dipolar couplings, and so is the preferred solution. It is concluded that the inclusion of geometry relaxation on rotation in this molecule is particularly important when using dipolar couplings to determine the potential for rotation about the ring C bond.

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Microwave spectrum andab initiocalculations of ethylbenzene: potential energy surface of the ethyl group torsion

Cited by 63 publications

References 17 publications

The conformational behavior of isobutylbenzene in CS₂/C₆D₁₂ solution at 300 K

The conformational behavior of isobutylbenzene in CS₂/C₆D₁₂ solution at 300 K

Concerning the internal rotational barrier and the experimental and theoretical ⁿJ(¹³C,¹³C) and ⁿJ (¹H,¹³C) in ethylbenzene-β-¹³C

An investigation of the conformation of 4-chloroethylbenzene as a solute in a nematic liquid crystalline solvent

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Microwave spectrum andab initiocalculations of ethylbenzene: potential energy surface of the ethyl group torsion

Cited by 63 publications

References 17 publications

The conformational behavior of isobutylbenzene in CS2/C6D12 solution at 300 K

The conformational behavior of isobutylbenzene in CS2/C6D12 solution at 300 K

Concerning the internal rotational barrier and the experimental and theoretical nJ(13C,13C) and nJ (1H,13C) in ethylbenzene-β-13C

An investigation of the conformation of 4-chloroethylbenzene as a solute in a nematic liquid crystalline solvent

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The conformational behavior of isobutylbenzene in CS₂/C₆D₁₂ solution at 300 K

The conformational behavior of isobutylbenzene in CS₂/C₆D₁₂ solution at 300 K

Concerning the internal rotational barrier and the experimental and theoretical ⁿJ(¹³C,¹³C) and ⁿJ (¹H,¹³C) in ethylbenzene-β-¹³C