A reinvestigation of singlet benzyne thermochemistry predicted by CASPT2, coupled-cluster and density functional calculations

Christopher J. Cramer; John J. Nash; Robert R. Squires

doi:10.1016/S0009-2614(97)00855-5

A reinvestigation of singlet benzyne thermochemistry predicted by CASPT2, coupled-cluster and density functional calculations

Christopher J. Cramer, John J. Nash, Robert R. Squires

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Abstract

Recent CASPT2 calculations of the heats of formation of the isomeric benzynes by R. Lindh and M. Schütz [Chem. Phys. Lett. 258 (1996) 409] are re-examined. The unrealistically low value reported for p-benzyne (132.7 kcal/mol) is shown to be an artifact of the use of incorrect CASSCF and CASPT2 energies for p-benzyne, as well as a flawed isodesmic reaction analysis. Use of the correct energies and an appropriate isodesmic reaction leads to excellent agreement between the calculated and measured heats of formation for p-benzyne. The performance of coupled-cluster methods and density functional theory in predicting benzyne thermochemistry and singlet-triplet splittings is also evaluated.

Original language	English (US)
Pages (from-to)	311-320
Number of pages	10
Journal	Chemical Physics Letters
Volume	277
Issue number	4
DOIs	https://doi.org/10.1016/S0009-2614(97)00855-5
State	Published - Oct 10 1997

Bibliographical note

Funding Information:
This work was supported by the National Science Foundation (CJC and RRS) and the Alfred P. Sloan Foundation (CJC).

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title = "A reinvestigation of singlet benzyne thermochemistry predicted by CASPT2, coupled-cluster and density functional calculations",

abstract = "Recent CASPT2 calculations of the heats of formation of the isomeric benzynes by R. Lindh and M. Sch{\"u}tz [Chem. Phys. Lett. 258 (1996) 409] are re-examined. The unrealistically low value reported for p-benzyne (132.7 kcal/mol) is shown to be an artifact of the use of incorrect CASSCF and CASPT2 energies for p-benzyne, as well as a flawed isodesmic reaction analysis. Use of the correct energies and an appropriate isodesmic reaction leads to excellent agreement between the calculated and measured heats of formation for p-benzyne. The performance of coupled-cluster methods and density functional theory in predicting benzyne thermochemistry and singlet-triplet splittings is also evaluated.",

author = "Cramer, \{Christopher J.\} and Nash, \{John J.\} and Squires, \{Robert R.\}",

note = "Funding Information: This work was supported by the National Science Foundation (CJC and RRS) and the Alfred P. Sloan Foundation (CJC).",

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AU - Cramer, Christopher J.

AU - Nash, John J.

AU - Squires, Robert R.

N1 - Funding Information: This work was supported by the National Science Foundation (CJC and RRS) and the Alfred P. Sloan Foundation (CJC).

PY - 1997/10/10

Y1 - 1997/10/10

N2 - Recent CASPT2 calculations of the heats of formation of the isomeric benzynes by R. Lindh and M. Schütz [Chem. Phys. Lett. 258 (1996) 409] are re-examined. The unrealistically low value reported for p-benzyne (132.7 kcal/mol) is shown to be an artifact of the use of incorrect CASSCF and CASPT2 energies for p-benzyne, as well as a flawed isodesmic reaction analysis. Use of the correct energies and an appropriate isodesmic reaction leads to excellent agreement between the calculated and measured heats of formation for p-benzyne. The performance of coupled-cluster methods and density functional theory in predicting benzyne thermochemistry and singlet-triplet splittings is also evaluated.

AB - Recent CASPT2 calculations of the heats of formation of the isomeric benzynes by R. Lindh and M. Schütz [Chem. Phys. Lett. 258 (1996) 409] are re-examined. The unrealistically low value reported for p-benzyne (132.7 kcal/mol) is shown to be an artifact of the use of incorrect CASSCF and CASPT2 energies for p-benzyne, as well as a flawed isodesmic reaction analysis. Use of the correct energies and an appropriate isodesmic reaction leads to excellent agreement between the calculated and measured heats of formation for p-benzyne. The performance of coupled-cluster methods and density functional theory in predicting benzyne thermochemistry and singlet-triplet splittings is also evaluated.

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A reinvestigation of singlet benzyne thermochemistry predicted by CASPT2, coupled-cluster and density functional calculations

Abstract

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