Shape resonances benzene

The shape resonances of benzene and some of its derivatives have been explored by a number of investigators using ETS (16,17,20, 36). With the exception of questions regarding pseudo-Jahn-Teller problems (37), for example in the alkyl-benzenes, substituent effects on the doubly-degenerate ground state anion near 1.1 eV... 

For example, the parentage of the l B2g "shape" resonance at 4.8 eV is not clear-cut, since it is known to decay Into electronically excited states of benzene as well as the ground state (39,40). It has been suggested previously that this anion must be described by an admixture of both shape and core-excited configurations (17). 

In Figure 4 we show the transmission spectrum of benzene at higher energies. The lowest feature Is the second "shape" resonance ( B2g). Above this lie several smaller features which must correspond primarily to core-excited states. Detailed studies of the decay channels of these resonances have not yet been carried out, although some Information is available. The vertical arrows in Figure 4 indicate the energies at which maxima occur in the excitation functions for Vi of the ground electronic state of ben-... 

Triarylmethyl cations (14) are propeller shaped, though the central carbon and the three ring carbons connected to it are in a plane The three benzene rings cannot all be in the same plane because of steric hindrance, though increased resonance energy would be gained if they could. 

R. F. C url, R. F. Smalley, and 11. W. Kroto were awarded the Nobel prize m chemistry in 199fe for the discovery of the soccer ball-shaped molecule C, . The enthalpy of combustion of (J o is 25 937 kj-mol 1 and its enthalpy of sublimation is +233 kj-mol 1 There are 90 bonds in of which 60 are single and 30 are double bonds. is like benzene in that it has a set of multiple bonds for which resonance structures may be drawn, (a) Determine the enthalpy of formation of Cfj) from its enthalpy of combustion, (h) Calculate the expected enthalpy of formation of from bond enthalpies, assuming the bonds to be isolated double and single bonds, (c) Is CMI more or less stable than predicted on the basis of the isolated bond model ... 

The nature and the possible structures of Xj and X2 are indicated by their electronic spectra. The absorption maximum at 425 nm in benzene and the shape of the spectrum of Xl9 the first short-lived intermediate (Figure 15), closely resemble those of the spectrum (A.max at 422 nm in methylene chloride) of TPP Mn(IV) prepared independently (31, 32, 33, 36), possibly indicating a charge-transfer complex (Figure 17). This assumption of a loose side-on complex resulting from a two-electron transfer is consistent with the previous results of the electron spin resonance (ESR) spectrum observed for an oxygencarrying species, TPP Mn(II) or substituted TPP Mn(II) (37). The... 

Having just seen a resonance description of benzene, let s now look at the alternative molecular orbital description. An orbital view of benzene makes clear the cyclic conjugation of the benzene molecule and the equivalence of the. six carbon-carbon bonds. Benzene is a planar molecule with the shape of a regular hexagon. All C-C-C bond angles are 120 , all six carbon atoms are sp -hybridized, and each carbon has a p orbital perpendicular to the plane of the six-membered ring. 

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