Lying Electronic Spectra

Compared with ground states of BHs, the low-lying excited states of these systems have been less studied from the semiempirical VB approaches. This is not accidental because even for benzene (1) the descriptions of the classical VB 

The calculated S-T energy gap may also be employed to deduce the kinetic reactivities of a given BH. One might notice that those BHs with large S-T gaps commonly behave relatively inert toward the various reactions, while those BHs 

Energies of the singlet ground and lowest triplet states and the corresponding S-T energy gaps for all benzenoid hydrocarbons shown in Fig. 1  

The lowest triplet spectra for some benzenoid hydrocarbons 

Lowest triplet spectra11 Lowest triplet spectra11 

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The absorption in the electronic spectrum lies in the normal range (Amax between 413 and 475 nm) (see Table I) for acyclic digermencs.60 63 75 A hypsochromic shift was observed for cyclotrigermene 75 (326 nm64). 

The meso-tetraphenylporphyrin complex [Zr(TPP)Cl2] has been prepared by reaction of H2TPP with ZrCl4 in boiling benzonitrile. The electronic spectrum of [Zr(TPP)Cl2] and the facile kinetics of TPP dissociation in acidic media suggest that the zirconium atom lies considerably out of the plane of the TPP ligand with both chlorine atoms being located on the same side of the TPP plane.708... 

Spectra of AH2 Molecules.—(i) Spectrum of H20. In the ground state of the H20 molecule all the orbitals represented in the Figure are fully occupied. These are the only low-lying orbitals of the molecule. No electronic spectrum of H20 is therefore expected until comparatively short wave-lengths are reached. In agreement, the first absorption of the molecule occurs as a continuum between 1830 and 1500 A (W ca. 1675 A Hopfield, Phys. Review, 1950, 77, 560). 

For a weak CF the ground CFT is 5Eg and the first excited CFT lies at A0 = 10Dq. The electronic spectrum for the octahedral complex also contains a transition A to the 3 Tig term arising from the free-atom 3H term (this is spin forbidden and consequently of a weak intensity, Table 73 and Fig. 123). 

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