Limitations of restricted open-shell self-consistent field calculations applied to molecules with multiple bonds. Electronic structure and geometry of the ground state of cyanocarbene

Harrison, J.; Dendramis, A.; Leroi, G. E.

doi:10.1021/ja00482a005

Cited by 23 publications

(14 citation statements)

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“…Thus, the best estimate of the vibrationless total atomization energy for X 3 A′′ HCCN is ∑D e ) 398.3 ( 0.6 kcal/mol. The harmonic zero-point vibrational energy for the ground 3 A′′ state was determined by the RCCSD(T) method to be 3868 and 3864 cm -1 with the cc-pVTZ and cc-pVQZ basis sets, respectively. Comparing the calculated harmonic vibrational frequencies (see Table 10 of ref 12) with the experimental fundamentals, 57,58 a maximum error of 0.3 kcal/ mol can be assigned to the calculated zero-point energy.…”

Section: Resultsmentioning

confidence: 99%

“…For both states, the HCNC molecule is well bent. At the RCCSD(T)/cc-pVnZ level of theory, the barrier to linearity for the 3 A′′ state was predicted to be 3450, 2977, 2876, and 2846 cm -1 for n ) D, T, Q, and 5, respectively. Thus, the barrier to linearity for a 3 A′′ HCNC is ∼9 times higher than that for X 3 A′′ HCCN.…”

Section: Resultsmentioning

confidence: 99%

“…9,11,13 The energetics of HCCN were investigated by Francisco. 10 At the highest level of theory applied in that study, QCISD(T)/6-311G-(3df,3pd)//QCISD(T)/6-311G(2d,2p), 14,15 the heat of formation at 0 K for X 3 A′′ HCCN was calculated to be 114.8 kcal/mol, and the singlet-triplet splitting was found to be 11.6 kcal/mol. Both calculated values are in reasonable agreement with the recent experimental data.…”

Section: Introductionmentioning

confidence: 81%

“…2 For HCNC, the singlet-triplet splitting was determined to be an order of magnitude smaller, being only 1.4 ( 0.6 kcal/mol. 2 The theoretical studies on cyanocarbene [3][4][5][6][7][8][9][10][11][12] focused on the problem of a ground-state equilibrium structure of the HCCN molecule, and those on HCNC are rather sparse. 9,11,13 The energetics of HCCN were investigated by Francisco.…”

Section: Introductionmentioning

confidence: 99%

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Ab Initio Heat of Formation and Singlet−Triplet Splitting for Cyanocarbene (HCCN) and Isocyanocarbene (HCNC)

Koput

2003

J. Phys. Chem. A

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The heat of formation and singlet-triplet splitting for cyanocarbene (HCCN) and isocyanocarbene (HCNC) have been determined in large-scale ab initio calculations, using the coupled-cluster method and basis sets of double-through quintuple-zeta quality. The heats of formation at 0 K for X 3 A′′ HCCN and X 1 A′ HCNC are predicted to be 116.8 and 140.5 kcal/mol, respectively, with the uncertainty estimated to be (2 kcal/mol or less. These values are substantially larger than those derived recently from experimental data, suggesting that the true values of the heats of formation must be at the upper end of their (large) experimental ranges. The singlet-triplet splittings are calculated to be 10.8 and 1.3 kcal/mol for HCCN and HCNC, respectively, with both values being in good agreement with the experimental data. The biradical nature of both molecules is discussed, on the basis of the results of calculations using the multireference methods.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 81%

Section: Introductionmentioning

confidence: 99%

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Ab Initio Heat of Formation and Singlet−Triplet Splitting for Cyanocarbene (HCCN) and Isocyanocarbene (HCNC)

Koput

2003

J. Phys. Chem. A

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“…They and others (36,37) have shown that the RHF SCF geometry optimization for open shell molecules containing multiple bond(s) tends to over-estimate the stability of the extreme, localized structures. SCF-CI optimization gives a completely delocalized structure with a global minimum lying below either of the local minima in the SCF hypersurface.…”

Section: Thioformylmethylenementioning

confidence: 99%

Abinitio molecular orbital studies on thiirene and its isomeric structures

Gosavi¹,

Strausz²

1983

Can. J. Chem.

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This article is dedicated to Professor Harry E. Gunning on the occasion of' his 65111 birthclqRATNAKAR K. GOSAVI and OTTO P. STRAUSZ. Can. J. Chem. 61, 2596Chem. 61, (1983. Ab initio molecular orbital calculations have been carried out on the lowest closed shell singlet states of six isomeric forms of CzHIS at the SCF and C1 levels using STO-3G and 6-3 1G" basis sets. Molecular geometries of the isomers and the activatcd complexes for their isomerization reactions were optimized by the energy gradient method at the SCF .level and the C1 calculations were performed at these geometries. In addition, the lowest singlet and triplet states of the. SCHCH diradical were also studied and their geometries optimized by the Restricted Hartree Fock method.The computed stabilities follow the orderThe pseudo antiaromatic character of the 4n-T electron thiirene is manifested by its drastically reduced C-S bond energy, -15 kcal mol-I as compared to the value of >40 kcal mol-' estimated for its 21-1-71. electron analog, thiirane. This explains why thiirenes can be stabilized in inert matrices at 8 K but decompose readily at higher temperatures. In agreement with experimental results the lowest energy path for the unimolecular decomposition of thiirene leads to thioketene via the lowest singlet (or triplet) state of thioformylmethylene.The ir frequencies calculated for thiirene from rib initio mo theory using 6-31'3 + polarization functions on the sulfur show reasonably good agreement with the experimental frequencies, confirming the carlier assignments of the ir spectrum of thiirene. Les stabilites calculCes sont dans I'ordrc suivant:Le caractere pseudo antiaromatique de I'Clectron 41-1-71. du thiirene se manifestc par la reduction drastique de son Cnergie de liaison C-S de = 15 kcal mol-' telle que comparCe 6 la valeur supkrieure 6 40 kcal mol-' CvaluCe pour I'Clectron 211-71. analogue du thiirane. Ceci expIique pourquoi on peut stabiliser les thiirenes dans des matrices inertes 6 8 K mais ils se decomposent rapidement i des tempkratures plus 6levCes. En accord avec les rCsultats expCrimentaux, la voie de plus faible Cnergie pour la dCcomposition unimolCculaire du thiirkne conduit au thiocetkne via I'Ctat singulet (ou triplet) le plus bas du thioformylene.Les frkquences ir calculCes pour le thiirene 6 partir de la theoric ab irlitio des OM utilisant la base 6-31G + les fonctions de polarisation du soufre montrent un accord raisonnablement bon avec les frkqucnces experimentales confirmant ainsi les attributions anterieures du spectre ir du thiirene.[Traduit par le journal]

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ChemInform Abstract: LIMITATIONS OF RESTRICTED OPEN‐SHELL SELF‐CONSISTENT FIELD CALCULATIONS APPLIED TO MOLECULES WITH MULTIPLE BONDS. ELECTRONIC STRUCTURE AND GEOMETRY OF THE GROUND STATE OF CYANOCARBENE

Harrison¹,

Dendramis

Leroi

1978

Chemischer Informationsdienst

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Limitations of restricted open-shell self-consistent field calculations applied to molecules with multiple bonds. Electronic structure and geometry of the ground state of cyanocarbene

Cited by 23 publications

References 1 publication

Ab Initio Heat of Formation and Singlet−Triplet Splitting for Cyanocarbene (HCCN) and Isocyanocarbene (HCNC)

Ab Initio Heat of Formation and Singlet−Triplet Splitting for Cyanocarbene (HCCN) and Isocyanocarbene (HCNC)

Abinitio molecular orbital studies on thiirene and its isomeric structures

ChemInform Abstract: LIMITATIONS OF RESTRICTED OPEN‐SHELL SELF‐CONSISTENT FIELD CALCULATIONS APPLIED TO MOLECULES WITH MULTIPLE BONDS. ELECTRONIC STRUCTURE AND GEOMETRY OF THE GROUND STATE OF CYANOCARBENE

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