Linear combination of hybrid orbitals: Cyclobutane as test-case (original) (raw)
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Tetra-radical and ionic S1/S0 conical intersections of cyclobutadiene
Chemical Physics, 2010
We have located two conical intersections between the first singlet excited (S 1) and singlet ground (S 0) states of cyclobutadiene (CBD) using the complete active space self-consistent field (CASSCF) method. One is the ionic-structure S 1 /S 0 conical intersection (CI ionic), which was located by carrying out a minimum-energy-path calculation from the Franck-Condon point of the HOMO to LUMO double-electron excited state, and the other is the tetra-radical S 1 /S 0 conical intersection (CI tetra), which was located by exploring the S 1 /S 0 degeneracy space. While CI ionic is only involved in the automerization of CBD, CI tetra is involved in not only the automerization but also the criss-cross reaction. It is possible for one of the highest constrained compounds, tetrahedrane, to be produced if S 1 excited CBD undergoes a transition to the S 0 state via the tetra-radical S 1 /S 0 conical intersection. In this paper, we discuss the possibility that unsubstituted tetrahedrane can be produced by irradiating CBD.
The vibrational spectra and conformations of polyhalogenated cyclobutanes
Journal of Molecular Structure, 1990
The vibrational spectra of 1 chloro-2,2,3,3-tetrafluoro-and 1 -cyano-2,2,3,3tetrafluorocyclobutane reveal that these compounds have a conformational equilibrium strongly shifted towards equatorial Cl and CN substituents, although to a smaller extent than for the chloro and cyanocyclobutane.
A simple geometrical path towards hybrid orbitals
Materials Research, 2014
It is shown that the standard sp n hybrid orbitals are orthogonal orbitals that minimize the total quadratic spread. This is done in a concise way that may improve the understanding of hybrid orbitals. The fact that maximally localized Wannier functions of crystalline materials may resemble hybrid orbitals is discussed.
The Journal of Chemical Physics, 1994
The high resolution IR spectrum of cyclobutane in a supersonic molecular beam was obtained for the region of 2981 to 2991 cm-1. The spectrum reveals four overlapping bands suggestive of vibrational mode coupling in the C-H stretching region. Ground state combination differences demonstrate that these bands__ Ac_:e io For originate from 2 different ground states, the symmetric and INT IS CF-., asymmetric ring puckering states. Evidence of vibrational mode, ' coupling is present in all four bands. The coupling depends on' J both J and the symmetry of the puckering state. A model:. coupling scheme involving two qualitatively different types of y couplings is developed to explain the observed spectrum..
Spectrochimica Acta Part A-molecular and Biomolecular Spectroscopy, 2011
Variable temperature (-55 to -100 °C) studies of the infrared spectra (3500-400 cm -1) of fluorocyclobutane, c-C 4H 7F, dissolved in liquid xenon have been carried out as well as the infrared spectra of the gas. By utilizing eight pairs of conformers at 10 different temperatures, the enthalpy difference between the more stable equatorial conformer and the axial form has been determined to be 496 ± 40 cm -1 (5.93 ± 0.48 kJ/mol). The percentage of the axial conformer present at ambient temperature is estimated to be 8 ± 1%. The ab initio MP2(full) average predicted energy difference from a variety of basis sets is 732 ± 47 cm -1 (9.04 ± 0.44 kJ/mol) and the average value of 602 ± 20 cm -1 from density functional theory predictions by the B3LYP method are significantly larger than the experimentally determined enthalpy value. By utilizing previously reported microwave rotational constants for the equatorial and axial conformers combined with ab initio MP2(full)/6-311+G(d,p) predicted structural values, adjusted r0 parameters have been obtained. The determined heavy atom structural parameters for the equatorial [axial] conformer are: distances (Å) C-F = 1.383(3) [1.407(3)], C α-C β = 1.543(3) [1.546(3)], C β-C γ = 1.554(3) [1.554(3)] and angles (°) ∠C αC βC γ = 85.0(5) [89.2(5)], ∠C βC αC β = 89.3(5) [89.2(5)], ∠F-(C βC αC β) = 117.4(5) [109.2(5)] and a puckering angle of 37.4(5) [20.7(5)]. The conformational stabilities, harmonic force fields, infrared intensities, Raman activities, depolarization ratios and vibrational frequencies have been obtained for both conformers from MP2(full)/6-31G(d) ab initio calculations and compared to experimental values where available. The results are discussed and compared to the corresponding properties of some other monosubstituted cyclobutanes with halogen and pseudo-halogen substituents.
Study the Electronic Structure of Tetragermanium-Cyclobutane Molecule Density Functional Theory
This work reports a theoretical study to investigate the electronic structure and electronic properties for a saturated molecules group by using density functional theory (DFT) at B3LYP level with bases set 6-31G. Cyclobutane molecule is original molecule before substitute carbon atoms by germanium atoms. The effect of substitute on cyclobutane molecule discussed based on the calculated electronic properties. The electronic properties included total energy, energy gap, ionization potential, electronic affinity, hardness, softness, electronegativity and electrophilicity, have been found with varying differences for each molecule, with comprehensive analysis of the calculated highest-occupied (Homo) and lowest-unoccupied orbital (Lumo) energies. These calculations have performed using Gaussian 03 package.
Nature of the Singlet and Triplet States of Cyclobutadiene as Revealed by Quantum Interference
Chemphyschem : a European journal of chemical physics and physical chemistry, 2015
The Generalized Product Function Energy Partitioning (GPF-EP) method has been applied to the description of the cyclobutadiene molecule. The GPF wave function was built in order to reproduce Generalized Valence Bond (GVB) and Spin-Coupled (SC)wave functions. The influence of quasi-classical and quantum interference contributions to each chemical bond of the system were analysed along the automerization reaction coordinate for the lowest singlet and triplet states. The results show that the interference effect on the π space reduces the electronic energy of the singlet cyclobutadiene relative to the second-order Jahn-Teller distortion, which takes the molecule from a D4h to a D2h structure. Our results also suggest that the π space of the 1B1g state of the square cyclobutadiene is composed of a weak 4-centre 4-electron (4c-4e) bond, while the 3A2g state has a 4-centre 2-electron (4c-2e) π bond. Finally, we also show that, although strain effects are non-negligible, the thermodynamics...
Cycloreversion of Formylcyclobutane Radical Anion: Two-Step Rotating Mechanism
The Journal of Physical Chemistry A, 2004
The [2+2] cycloreversion reaction of formylcyclobutane radical anion (c-C 4 H 7-CHO •-) has been investigated at the UB3LYP level with the augmented Dunning's correlation-consistent polarized valence double-basis set supplied with four even-tempered sp shells. Very diffuse p-π*-like singly occupied orbitals (SOMO) are found for the cC 4 H 7-CHO •and product CH 2 CHCHO •radical anions, necessitating the use of a rather diffuse basis set for mechanistic study. The respective electron affinities of cC 4 H 7-CHO and CH 2 CHCHO are calculated to be 5.4 and 16.1 kcal/mol, showing the ability to bind an extra electron. The intermediate structure • (CH 2) 3 CHCHOis found to be a valence-bound distonic anion apt to the elimination of C 2 H 4. The present two-step "rotating" cycloreversion mechanism for cC 4 H 7-CHO •is formally similar to the biradical one for neutral cyclobutane structures, but with evidently lower potential barrier. For efficient electronattachment catalysis, the extra electron should be trapped by suitable functional groups in some orbitals with substantial overlap with the σ*-orbitals of the cyclobutane structure.