Quantum-Chemical ab initio Calculations on the Three Isomers of Diborabenzene (C4H4B2)

AbstractQuantum-chemical ab initio calculations up to the ZPE+CCSD(T)/aug-cc-pVTZ//MP2/6- 311++G** level were performed on three possible structural isomers of diborabenzene (C4H4B2). All three molecules were found to be local minima on the C4H4B2 energy surface and to have closed shell singlet ground states. While the ground states of the 1,3- and 1,4-isomer are planar and of C2v and D2h symmetry, respectively, 1,2-diborabenzene is non-planar with a C2 axis passing through the center of the BB bond and the middle of the opposite carbon-carbon bond as the only symmetry element. The energetically most favourable 1,3-diborabenzene was found to be about 19 and 36 kcal/mol lower in energy than the 1,2- and the 1,4-isomer. Planar 1,3- and 1,4-diborabenzene have three doubly occupied π orbitals while non-planar 1,2-diborabenzene has also three doubly occupied orbitals which can be derived from the π orbitals of its 3.7 kcal/mol energetically less favourable planar form (“π-like” orbitals). The lowest unoccupied orbitals of all three isomers have σ symmetry with large coefficients at the two boron atoms. These orbitals are lower in energy than the lowest unoccupied molecular orbitals (LUMOs) of e. g. benzene and pyridine and might cause pronounced acceptor properties which could be one of the reasons for the elusiveness of the title compounds. The results of bond separation reactions show that cyclic conjugation stabilizes all three diborabenzenes relative to their isolated fragments. The most effective stabilization energy of about 24 kcal/mol was found for the energetically lowest 1,3-isomer. This value amounts to approximately one third of the experimental value for the bond separation energy of pyridine. In all cases the energetically lowest triplet states are significantly (16 - 24 kcal/mol) higher in energy than the singlet ground states. Also among the triplets the 1,3-isomer is the energetically most fabourable species.

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Quantum-Chemical Ab Initio Calculations on Inda- and Thallabenzene (C5H5In and C5H5Tl) and their Structural Isomers η5-C5H5In and η5-C5H5Tl

Australian Journal of Chemistry ◽

10.1071/ch17472 ◽

2018 ◽

Vol 71 (3) ◽

pp. 102

Author(s):

Emma Persoon ◽

Yuekui Wang ◽

Gerhard Raabe

Keyword(s):

Ab Initio ◽

Quantum Chemical ◽

Density Functional ◽

Single Point ◽

Normal Modes ◽

Dft Method ◽

Basis Sets ◽

Triplet States ◽

Structural Isomers ◽

Td Dft

Quantum-chemical ab initio, time-independent, as well as time-dependent density functional theory (TD-DFT) calculations were performed on the so far elusive heterocycles inda- and thallabenzene (C5H5In and C5H5Tl), employing several different methods (MP2, CISD, CCSD, CCSD(T), BD, BD(T), QCISD, QCISD(T), CASSCF, DFT/B3LYP), effective core potentials, and different basis sets. While calculations on the MP2 level predict the ground states of the title compounds to be singlets with the first triplet states between 13 and 15 kcal mol−1 higher in energy, single point calculations with the QCISD(T), CCSD(T), and BD(T) methods at CCSD-optimized structures result in energy differences between the singlet and the triplet states in the range between 0.3 and 2.1 kcal mol−1 in favour of the triplet states. According to a CASSCF(8,8) calculation the triplets are also more stable by about 2.5–2.9 kcal mol−1. Calculations were also performed for the C5v-symmetric η5 structural isomers (cyclopentadienylindium, CpIn, and cyclopentadienylthallium, CpTl, Cp = C5H5) of the title compounds. At the highest level of theory employed in this study, C5H5In is between 79 and 88 kcal mol−1 higher in energy than CpIn, while this energy difference is even larger for thallabenzene where C5H5Tl is energetically between 94 and 102 kcal mol−1 above CpTl. In addition we report on the UV/vis spectra calculated with a TD-DFT method as well as on the spectra of the normal modes of C5H5In and C5H5Tl. Both types of spectra might facilitate identification of the title compounds eventually formed in photolysis or pyrolysis experiments.

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Geometric and Energetic Data from Ab Initio Calculations of Haloethene, Haloimine, Halomethylphosphine, Haloiminophosphine, Halodiazene, Halodiphosphene and Halocyclopropane

10.26434/chemrxiv.9895874.v1 ◽

2019 ◽

Author(s):

Kridtin Chinsukserm ◽

Wanutcha Lorpaiboon ◽

Peerayar Teeraniramitr ◽

Taweetham Limpanuparb

Keyword(s):

Ab Initio Calculations ◽

Ab Initio ◽

Quantum Chemical ◽

Theoretical Data ◽

Geometric Optimization ◽

Basis Set ◽

Halogenated Compounds ◽

Wolfram Mathematica

<p>This article presents theoretical data on geometric and energetic features of halogenated compounds of cyclopropane (∆) and ethene (C=C), imine (C=N), methylphosphine (C=P), iminophosphine (N=P), diazene (N=N) and diphosphene (P=P). The data were obtained from <i>ab initio</i> geometric optimization and frequency calculations at HF, B3LYP, MP2 and CCSD levels of theory on 6-311++G(d,p) basis set. Input structures were generated by shell scripts and run by Q-Chem quantum chemical package. The output files were processed to extract geometric and energetic information by Wolfram Mathematica.</p>

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Excitons in poly(para phenylene vinylene): a quantum-chemical perspective based on high-level ab initio calculations

Physical Chemistry Chemical Physics ◽

10.1039/c5cp07077e ◽

2016 ◽

Vol 18 (4) ◽

pp. 2548-2563 ◽

Cited By ~ 33

Author(s):

Stefanie A. Mewes ◽

Jan-Michael Mewes ◽

Andreas Dreuw ◽

Felix Plasser

Keyword(s):

Ab Initio Calculations ◽

Ab Initio ◽

Quantum Chemical ◽

Phenylene Vinylene ◽

High Level ◽

Quantum Chemical Computations

Exciton analyses of high-level quantum-chemical computations for poly(paraphenylene vinylene) reveal the nature of the excitonic bands in PPV oligomers.

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Ab Initio calculations of the stabilization energies of the conformational and the structural isomers of C3H7X where X = F, Cl, and Br

Journal of Computational Chemistry ◽

10.1002/jcc.10047 ◽

2002 ◽

Vol 23 (10) ◽

pp. 966-976 ◽

Cited By ~ 4

Author(s):

Mustafa R. Helal ◽

Yaser A. Yousef ◽

Akef T. Afaneh

Keyword(s):

Ab Initio Calculations ◽

Ab Initio ◽

Structural Isomers ◽

Stabilization Energies

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Ab initio calculations on vibronic coupling in the lower triplet states of pyrimidine

Journal of the American Chemical Society ◽

10.1021/ja00050a038 ◽

1992 ◽

Vol 114 (24) ◽

pp. 9544-9551 ◽

Cited By ~ 10

Author(s):

W. J. Buma ◽

M. C. J. M. Donckers ◽

E. J. J. Groenen

Keyword(s):

Ab Initio Calculations ◽

Ab Initio ◽

Vibronic Coupling ◽

Triplet States

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Cleavage of the radical cations of alkenes; 1-butene and 4,4-dimethyl-1-pentene. Ab initio calculations on the interaction between the allyl and alkyl radical and carbocation moieties

Canadian Journal of Chemistry ◽

10.1139/v91-202 ◽

1991 ◽

Vol 69 (9) ◽

pp. 1365-1375 ◽

Cited By ~ 14

Author(s):

Xinyao Du ◽

Donald R. Arnold ◽

Russell J. Boyd ◽

Zheng Shi

Keyword(s):

Ab Initio Calculations ◽

Ab Initio ◽

Radical Cation ◽

Alkyl Radical ◽

Radical Cations ◽

Molecular Orbital Calculations ◽

Allyl Radical ◽

Allyl Cation ◽

Tert Butyl ◽

Carbon Carbon Bond

Carbon–carbon bond cleavage of the radical cations of 1-butene [Formula: see text] and 4,4-dimethyl-1-pentene [Formula: see text] will generate the allyl and alkyl radical and carbocation fragments. Alternative bonding arrangements between the allyl and methyl moieties in [Formula: see text] and between the allyl and tert-butyl moieties in [Formula: see text] possible metastable intermediates or transition states preceding complete separation of the fragments, have been investigated by ab initio molecular orbital calculations. Structures were fully optimized at the UHF/6-31G* or UHF/STO-3G levels, and some of the calculations on [Formula: see text] were expanded with single point MP2/6-31G*//UHF/6-31G* computations. The C4H8+ radical cation, having a structure similar to that of 1-butene, is more stable than the separated fragments: 183 kj mol−1 lower in energy than the sum of the energies of the allyl cation and the methyl radical, and 385 kJ mol−1 lower than the sum of the energies of an allyl radical and a methyl cation, at the MP2/6-31G* level. The corresponding values at the UHF/STO-3G level are 276 and 415 kj mol−1, respectively. There is less bonding interaction between the allyl and tert-butyl moieties in [Formula: see text] The summation of the energies of the allyl radical and tert-butyl cation is 123 kj mol−1 lower than the summation of the energies of the allyl cation and tert-butyl radical, and 115 kJ mol−1 higher in energy than the bonded radical cation [Formula: see text] at the UHF/STO-3G level. These calculated values are compared with thermochemical data and with experimental results on the cleavage of these, and related, radical cations. Key words: radical cation, cleavage, ab initio calculations, electron transfer, photochemistry.

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Quantum-Chemical Ab Initio Calculations on Ala-(C5H5Al) and Galabenzene (C5H5Ga)

Zeitschrift für Naturforschung A ◽

10.5560/zna.2014-0015 ◽

2014 ◽

Vol 69 (7) ◽

pp. 349-359 ◽

Cited By ~ 2

Author(s):

Stefanie Mersmann ◽

Halima Mouhib ◽

Matthias Baldofski ◽

Gerhard Raabe

Keyword(s):

Ab Initio ◽

Quantum Chemical ◽

Density Functional ◽

Normal Modes ◽

Closed Shell ◽

Basis Sets ◽

Moderate Intensity ◽

Spectral Curves ◽

Singlet States ◽

Td Dft

1Quantum-chemical ab initio and time-dependent density functional theory (TD-DFT) calculations employing various basis sets were used to elucidate the spatial as well as the electronic structure of C5H5Al () and C5H5Ga (2) (ala- and galabenzene). The lowest closed shell singlet states of both compounds were found to have a non-planar structure of CS symmetry with C-X-C bond angles of about 116° (MP2/6-311++G**) and 125° (CCSD/aug-cc-pVDZ). At approximately 103°, the corresponding angles of the lowest triplets are significantly smaller. The lowest triplet state of alabenzene is also non-planar (CS) at the MP2 level while optimization with the CCSD and the CASPT2 method resulted in planar structures with C2v symmetry. The corresponding state of galabenzene has C2v symmetry at all levels of optimization. The relative stability of the lowest closed shell singlet and the lowest triplet (ΔE(T1-S0)) state is small and its sign even strongly method-dependent. However, according to the highest levels of theory applied in this study the singlet states of both molecules are slightly lower in energy than the corresponding triplets with singlet/triplet gaps between about 0.5 and 5.8 kcal/mol in favour of the singlet states. Most of the applied methods give a slightly smaller splitting for ala- than for galabenzene. Independent of the applied method (TD-DFT/CAM-B3LYP/6-311++G(3df,3pd)//MP2/6- 311++G** or SAC-CI/6-31++G(3df,3pd)//MP2/6-311++G**), the general shape of the calculated UV/VIS spectral curves are quite similar for the lowest singlet states of ala- and galabenzene, and the same applies to the spectra of the normal modes. The calculated UV/VIS spectra of C5H5Al and C5H5Ga are featured by long wavelength bands of moderate intensity around 900 nm at the TD-DFT and between 1300 and 1500 nm at the SAC-CI level. According to both methods these bands are predominantly due to HOMO(π)→LUMO(σ*) transitions. The results of isodesmic bond separation reactions for the singlet states indicate some degree of stabilization due to delocalization in both of the title compounds. With our best values between 29 and 32 kcal/mol this stabilization appears to be only slightly less than the previously reported value for borabenzene (∼38 kcal/mol).

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