Chemical orbital theory

Keywords Chemical orbital theory. Electron delocalization. Frontier orbital. Orbital amplitude, Orbital energy, Orbital interaction. Orbital mixing rule, Orbital phase, Orbital phase continuity, Orbital phase environment. Orbital synunetry, Reactivity, Selectivity... 

The theory of two-orbital interactions has been described in the preceding sections. The elements of the chemical orbital theory also include the theories of of three-orbital interactions and cyclic interactions of more than two orbitals (Scheme 1). 

Another theory as an important element of the chemical orbital theory is an orbital phase theory for cyclic interactions of more than two orbitals. The cyclic orbital interactions are controlled by the continuity-discontmuity of orbital phase [21-23]. 

Keywords Cycloadditions, Chemical orbital theory. Donor-acceptor interaction. Electron delocalization band. Electron transfer band, Erontier orbital. Mechanistic spectrum, NAD(P)H reactions. Orbital amplitude. Orbital interaction. Orbital phase. Pseudoexcitation band. Quasi-intermediate, Reactivity, Selectivity, Singlet oxygen. Surface reactions... 

Molecules have some occupied and some unoccupied orbitals. There occur diverse interactions (Scheme 1) when molecules undergo reactions. According to the frontier orbital theory (Sect 3 in Chapter Elements of a Chemical Orbital Theory by Inagaki in this volume), the HOMO d) of an electron donor (D) and the LUMO (fl ) of an electron acceptor (A) play a predominant role in the chemical reactions (delocalization band in Scheme 2). The electron configuration D A where one electron transfers from dio a significantly mixes into the ground configuration DA where... 

Thermal dimerization of ethylene to cyclobutane is forbidden by orbital symmetry (Sect 3.5 in Chapter Elements of a Chemical Orbital Theory by Inagaki in this volume). The activation barrier is high E =44 kcal mof ) [9]. Cyclobutane cannot be prepared on a preparative scale by the dimerization of ethylenes despite a favorable reaction enthalpy (AH = -19 kcal mol" ). Thermal reactions between alkenes usually proceed via diradical intermediates [10-12]. The process of the diradical formation is the most favored by the HOMO-LUMO interaction (Scheme 25b in chapter Elements of a Chemical Orbital Theory ). The intervention of the diradical intermediates impfies loss of stereochemical integrity. This is a characteric feature of the thermal reactions between alkenes in the delocalization band of the mechanistic spectrum. 

The HOMO amplitude of olefins determines (Sect 3.4 in Chapter Elements of a Chemical Orbital Theory by Inagaki in this volume) which carbon atom attracts... 

The theory of interaction between a pair of orbitals, (J) and (Scheme la) is well established (Chapter Elements of a Chemical Orbital Theory by Inagaki in this volume) and snccessfnlly applied to nnderstanding and designing molecnles and reactions (Chapter A Mechanistic Spectrum of Chemical Reactions by Inagaki in this volnme). Here, we describe a theory of the interaction of three orbitals, (j), (J), and (j), (Scheme lb). The interactions include indirect interactions of... 

The frontier orbital theory was developed for electrophilic aromatic substitution (Chapter Elements of a Chemical Orbital Theory by Inagaki in this volume). Application is successful to the ortho-para orientation (Scheme 23a) for the benzenes substituted with electron donating groups. The ortho and para positions have larger HOMO amplitudes. The meta orientation (Scheme 23b) for the electron accepting groups is under control of both HOMO and the next HOMO [25]. 

Molecular properties and reactions are controlled by electrons in the molecules. Electrons had been thonght to be particles. Quantum mechanics showed that electrons have properties not only as particles but also as waves. A chemical theory is required to think abont the wave properties of electrons in molecules. These properties are well represented by orbitals, which contain the amplitude and phase characteristics of waves. This volume is a result of our attempt to establish a theory of chemistry in terms of orbitals — A Chemical Orbital Theory. 

The chemical orbital theory has been established almost as described in this volume. The theory is useful and reliable for thinking about molecules and reactions. In the future, applications will shift more and more from understanding to designing molecules and reactions. 

See electron proton bonds, chemical orbital theory ionization radioactivity fission. 

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