Pentagon Stability: Cyclic Delocalization of Lone Pairs through σ Conjugation and Design of Polycyclophosphanes

Topics in Current Chemistry

2009

Self Cite

A chemical orbital theory is useful in inorganic chemistry. Some applications are described for understanding and designing of inorganic molecules. Among the topics included are: (1) valence electron rules to predict stabilities of three- and four-membered ring metals and for those of regular octahedral M(6) metal clusters solely by counting the number of valence electrons; (2) pentagon stability (stability of five- relative to six-membered rings in some classes of molecules), predicted and applied for understanding and designing saturated molecules of group XV elements; (3) properties of unsaturated hydronitrogens N( m )H( n ) in contrast to those of hydrocarbons C( m )H( n ); (4) unusually short nonbonded distances between metal atoms in cyclic molecules.

Section: Applicationssupporting

confidence: 76%

Section: Theorymentioning

confidence: 85%

Section: Theorymentioning

confidence: 99%

Section: Applicationsmentioning

confidence: 99%

Section: Applicationsmentioning

confidence: 99%

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Orbitals in Inorganic Chemistry: Metal Rings and Clusters, Hydronitrogens, and Heterocyles

Topics in Current Chemistry

2009

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

Wang

J of Physical Organic Chem

2007

Some 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.

Orbital Phase Design of Diradicals

Wang

2009

Orbitals in Chemistry

Over the last three decades the rational design of diradicals has been a challenging issue because of their special features and activities in organic reactions and biological processes. The orbital phase theory has been developed for understanding the properties of diradicals and designing new candidates for synthesis. The orbital phase is an important factor in promoting the cyclic orbital interaction. When all of the conditions: (1) the electron-donating orbitals are out of phase; (2) the accepting orbitals are in phase; and (3) the donating and accepting orbitals are in phase, are simultaneously satisfied, the system is stabilized by the effective delocalization and polarization. Otherwise, the system is less stable. According to the orbital phase continuity requirement, we can predict the spin preference of π-conjugated diradicals and relative stabilities of constitutional isomers. Effects of the intramolecular interaction of bonds and unpaired electrons on the spin preference, thermodynamic and kinetic stabilities of the singlet and triplet states of localized 1,3-diradicals were also investigated by orbital phase theory. Taking advantage of the ring strains, several monocyclic and bicyclic systems were designed with appreciable singlet preference and kinetic stabilities. Substitution effects on the ground state spin and relative stabilities of diradicals were rationalized by orbital interactions without loss of generality. Orbital phase predictions were supported by available experimental observations and sophisticated calculation results. In comparison with other topological models, the orbital phase theory has some advantages. Orbital phase theory can provide a general model for both π-conjugated and localized diradicals. The relative stabilities and spin preference of all kinds of diradicals can be uniformly rationalized by the orbital phase property. The orbital phase theory is applied to the conformations of diradicals and the geometry-dependent behaviors. The insights gained from the orbital phase theory are useful in a rational design of stable 1,3-diradicals.