Orbital Phase Theory Research Articles

Orbital Phase Theory and the Diastereoselectivity of Some Organic Reactions

The orbital phase refers to the relationship between orbitals that originates from their wave character. We show here that the orbital phase essentially determines the diastereoselectivity of the following three organic reactions. 1) Torquoselectivity of the electrocyclicring-opening reaction of 3-substituted cyclobutenes; 2) Contradictory torquoselectivity of the retro-Nazarov reaction; 3) Diastereoselectivity in electrophilic addition to substituted ethylenes.

ChemInform Abstract: Orbital Phase Design of Diradicals

AbstractReview: 164 refs.

ChemInform Abstract: An Orbital Phase Theory

AbstractReview: 146 refs.

The Origin of Cis Effect in 1,2-Dihaloethenes: The Quantitative Comparison of Electron Delocalizations and Steric Exchange Repulsions

Abstract The “cis effect” is a phenomenon in which the cis isomer is more stable than the corresponding trans isomer or almost the same stability in some molecules with double bonds. In order to clarify the predominant factor of this cis effect in the 1,2-dihaloethenes (XHC=CHX; 1: X=F, 2: Cl, and 3: Br), the energetic amount of electron delocalizations and steric exchange repulsions were theoretically estimated using the natural bond orbital (NBO) theory at MP2/6-311++G(3df,3pd) level. Two delocalization mechanisms, periplanar hyperconjugations (synperiplanar and antiperiplanar effects) and halogen lone pair delocalizations into the C=C bond antibonding orbitals (LP effect), were found as the cis stabilizing forces, in which the total amount of LP effect was greater than those of periplanar effects, the dominant factor of the cis effect. Moreover, the origin of the cis preference of the LP effect was clearly elucidated with the application of orbital phase theory, i.e., the cyclic orbital interaction was continuous only in the cis isomers of 1–3. The total steric exchange repulsion between two isomers were all trans stabilizing and their energetic gains were 1.26, 16.48, and 23.22 kJ mol−1 for 1, 2, and 3, respectively. These steric forces obviously counteract against cis preferable delocalization mechanisms, especially in compounds with larger halogen atoms, but their amounts are apparently less than those of electron delocalizations (29.82, 40.00, and 34.46 kJ mol−1 for 1, 2, and 3, respectively). Therefore, electron delocalization, not exchange repulsion, has the largest responsibility for the relative energies of 1,2-dihaloethene systems. The importance of this work is the quantitative elucidation of the dominance of delocalization mechanisms over steric effects on the electronic and energetic view of a simple molecular structure.

Stable silicon‐centered localized singlet 1,3‐diradicals XSi(GeY2)2SiX: theoretical predictions

AbstractSome localized singlet 1,3‐σ‐diradicals, XSi(GeY2)2SiX, (X = H, CH3, SiH3, C(CH3)3, NH2 for X = F; Y = H, CH3, OH, NH2, SiH3 for X = H) are theoretically designed by the orbital phase theory, the density functional theory (DFT) calculations , the second order Møller–Plesset perturbation theory (MP2), and the complete active space self‐consistent field (CASSCF) methods. The silicon‐centered singlet diradicals are more stable than the lowest triplets and than the bicylic σ‐bonded isomers if the isomers exist. The most stable singlet diradicals are not the π‐type diradicals, but the σ‐type diradicals where the radicals interact with each other through the SiGe bonds in the four‐membered rings. Copyright © 2007 John Wiley & Sons, Ltd.

Theoretical design of singlet localized σ-diradicals: C(MH 2) 3C (M = Si, Ge, Sn, Pb)

Some localized singlet 1,3-σ-diradicals, C(MH 2) 3C, (M = Si, Ge, Sn, Pb) were theoretically designed by the orbital phase theory and density functional theory calculations. The bicyclic carbon-centered singlet diradicals were more stable than the lowest triplets. Except for M = C, σ-bonded isomers were not located for 1,3-σ-diradicals. 1,4-σ-diradicals, C(M 2H 4) 3C, also had singlet ground states, but they were less stable than σ-bonded isomers.

An orbital phase theory for the torquoselectivity of the ring-opening reactions of 3-substituted cyclobutenes: geminal bond participation.

We apply an orbital phase theory to the torquoselectivity of the electrocyclic reactions of 3-substituted (X) cyclobutenes. The torquoselectivity is shown to be controlled by the orbital-phase relation of the reacting pi(CC) and sigma(CC) bonds with the sigma(CX) bond geminal to the sigma(CC) bond to be cleaved. The inward rotation of electron-donating sigma(CX) bonds and outward rotation of electron-withdrawing sigma(CX) bonds have been deduced from the orbital-phase theory. Enhancement of the inward rotation by the electron-donating capability of the sigma(CX) bonds is confirmed by the correlation between the torquoselectivity and sigma(CX) orbital energy. The orbital overlaps between the geminal sigma(CX) (sigma(CH)) and sigma(CC) bonds are found to be important as well. Unsaturated substituents with low-lying unoccupied pi orbitals also promote the inward rotation.

Theoretical designs of singlet localized 1,3-diradicals.

Spin preference and S-T gaps of localized 1,3-diradicals were studied by an orbital phase theory and theoretical calculations. The orbital phase theory was applied to rationalize thermodynamic and kinetic stabilities of diradicals. We theoretically designed some singlet localized 1,3-diradicals, substituted trimethylenes, which are more stable than the lowest triplets. Some diradicals with the four-membered rings, 2,4-disilacyclobutane-1,3-diyls, were designed and shown to have singlet ground states and to be more stable than the sigma-bonded isomers, 2,4-disilabicyclo[1.1.0]butanes. The ab initio calculations supported predictions of the stable carbon-centered localized singlet 1,3-diradicals.

Pentagon Stability in Cycloarsanes

The orbital phase theory leads to the prediction that the saturated arsenic cyclic molecules prefer pentagons, which is substantiated by the negative strain energy of cyclic As 5 H 5 . The puckered five-membered arsenic ring is an important structural unit for the pentagon stability. Possible structures and conformers of polycycloarsanes As 8 H 4 , As 11 H 3 , "roof-like" and "cage-like" As 12 H 4 , As 13 H 3 , As 14 H 2 , and As 15 H 3 with relatively low strain energies were predicted due to many puckered pentagon units in them. The low stability of the dodecahedron As 20 with 12 planar pentagon units was suggested by the high strain energy.

Pentagon stability: cyclic delocalization of lone pairs through sigma conjugation and design of polycyclophosphanes.

The orbital-phase theory was applied to propose pentagon stability in a well-defined manner. Cyclic delocalization of the lone pair electrons on the five-membered ring atoms through the vicinal sigma bonds was shown to be favored by the orbital-phase properties. The pentagon stability was found to be outstanding in saturated phosphorus five-membered rings in the puckered conformation, and was substantiated by the negative strain energy of cyclopentaphosphane, P(5)H(5) (3). The relative increments of the remarkable increase in the strain energies of protonation on the different atoms in the most stable conformers supported the significance of the cyclic delocalization of the lone pairs. Pentagon stability led to the design of three novel polycyclic phosphanes, P(12)H(4) (18), P(13)H(3) (19), and P(14)H(2) (20), with low strain energies due to many puckered pentagon units in them. The low stability of the dodecahedron P(20) (22) was suggested by the high strain energy due to its planar pentagon units. The pentagon stability is less significant in the saturated nitrogen ring molecules due to the greater energy gap between the n and sigma orbitals.

Orbital phase control of conformations of alkyne derivatives

Stable conformers of the alkynes bis-substituted by donor (NH 2 ) and/or acceptor (CHO) groups were predicted by the orbital phase theory and confirmed by the ab initio and density functional calculations. The most stable conformers are planar in the mono-, di-, and triacetylenes substituted by a donor on terminal carbon atom and an acceptor on the other one. The stable conformers of those with donors or acceptors on both terminal carbon atoms are orthogonal. In the most stable conformers of the equatorial isomers of the hypervalent derivatives (RC CSiF 4 − : R NH 2 ; CHO), the donor ( n N ) orbital and σ SiF eq ∗ with same π CC bond orbitals, or the acceptor ( π CO ∗ ) orbital and σ SiF eq ∗ interact with different π CC bond orbitals. Graphic

Orbital phase control of the preferential branching of chain molecules.

The orbital phase theory was applied to the stabilities of the branched isomers (1) of E(4)H(10) (E = C, Si, Ge, Sn) relative to the normal ones (2). The orbital phase prediction was confirmed by ab initio molecular orbital (MO) and density functional theory (DFT) calculations as well as by some experimental results. Further applications to the relative stabilities of other alkane and alkene isomers lead to the preference of the branched to the normal isomers, the neopentane-type to isobutane-type branching, the terminal to inner methyl branching, and the methyl to ethyl inner substitution in the longer alkanes, as well as the preference of isobutene to 2-butene moieties. The preferential stabilization of the branched isomers was shown to be general and controlled by the orbital phase.

Orbital phase control of the conformations of α- and β-substituted enamines and vinyl ethers

The conformational stabilities of the α- and β-substituted enamines and vinyl ethers were predicted by orbital phase theory and confirmed by ab initio molecular orbital calculations. Cyclic interaction significantly occurs among the nonbonding orbital nY for the lone pair on the hetero atom Y (N in the enamines or O in the ethers), the π and π* orbitals of the CC bond, and the σC-H or σ*C-X orbitals on the substituent CH2X. The cyclic -nY-π-σC-H-π*- interaction is favored by the orbital phase continuity in the α-substituted molecules, while the cyclic -nY-π-σ*C-X-π*- interaction is favored in the β-substituted molecules. The most stable conformation was then predicted to be synperiplanar or (pseudo)equatorial in the α-substituted molecules and anticlinical or (pseudo)axial in the β-substituted molecules.

Orbital Phase Control of Trigonal Pyramidal Structures of Tricoordinated Metal Complexes

Abstract Trigonal pyramidal structures of some tricoordinated metal complexes ML3 (M = Mg, Al, Si) are predicted by an orbital phase theory and confirmed by ab initio molecular orbital calculations to have acute L–M–L angles in spite of the steric congestion.