Benzene orbital regions

Figure 21.9 The Orbital Regions of the Delocalized Pi Orbitals in Benzene by the Hiickel Method. Positive regions are in black and...

FIGURE 113 (a) The framework of bonds shown in the tube model of benzene are cr bonds (b) Each carbon is sp hybridized and has a 2p orbital perpendicular to the cr framework Overlap of the 2p orbitals generates a tt system encompass mg the entire ring (c) Electrostatic potential map of benzene The red area in the center corresponds to the region above and below the plane of the ring where the tt electrons are concentrated... 

According to the orbital hybridization model benzene has six tt elec Irons which are shared by all six sp hybridized carbons Regions of high TT electron density are located above and below the plane of the ring... 

Using the molecular orbital method, Coulson showed how certain electrons in benzene, namely, the p electrons, can move over the whole molecule instead of being restricted to the region between two particular atoms. 93 Coulson, collaborating later with Longuet-Higgins and the French theoreticians Pascaline and Raymond Daudel and Alberte and Bernard Pullman, was to become a major presence in quantum chemistry. But on the whole, Coulson said, he was inclined to characterize the period from 1933 until the end of the Second World War as the "Mulliken Era. "94... 

Several investigators132,179 184 have examined the ultraviolet absorption spectra of tetraphenylantimony halides. The fine structure in the 250-270 ny< region is characteristic of unperturbed benzene rings and indicates that there is comparatively little pit-dn resonance between it orbitals of the benzene ring and the vacant d orbitals of the antimony atom. 

Solutions of iodine in organic solvents illustrate an important aspect of solution chemistry. Iodine vapor has a deep purple color as a result of absorption of light in the visible region, which shows a maximum at 538 nm. Solutions of iodine have absorption maxima that vary with the nature of the solvent, and when I2 is dissolved in a solvent such as CC14 or heptane the solution has a blue-purple color. However, if the solvent is benzene or an alcohol the solution is brown. This difference in color is the result of the change in the relative energy of the n and n orbitals of the I2 molecule as a result of their interaction with the solvent. The interaction is very weak for solvents such as CCI4 and heptane so in... 

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