Benzene charge cloud

It is noteworthy that Coulson et al. [50], calculating the electron density in benzene in the plane 0.35 above the molecular plane, found that there is only a very small region directly above each of the six carbon nuclei where the charge density of the n electrons is as great as that of the a electrons, meaning that the n electron charge cloud does overlap considerably with that of a electrons. Thus this calculation threw a considerable doubt on the validity of the a—n separation [51],... 

The influence of this cloud of negative charge on the type of reagents that will attack benzene is discussed below (p. 131). 

It is to be expected that attack by nucleophiles on an unsubstituted benzene nucleus will be much more difficult than attack by electrophiles. This is so (o) because the n electron cloud of the nucleus (p. 130) is likely to repel an approaching nucleophile, and (b) because its n orbital system is much less capable of delocalising (and so stabilising) the two extra electrons in the negatively charged (72), than the positively charged Wheland intermediate (73) ... 

The cyclopentadiene anion is stabilized by five equivalent resonance structures. The anion is an aromatic anion by virtue of it being a six-jr-electron system. The indenyl anion is stabilized by a total of seven resonance contributors. However, they are nonequivalent and all but one require that the aromatic cloud of the benzene ring is disrupted. Thus, while the negative charge is well delocalized, the resonance stabilization is less than that of the cyclopentadiene system. Thus the proton is not as easily removed, making indene a weaker acid. 

The ring compound, benzene, C6H6, is given in a tr-bond picture only but a similar streamer picture can be drawn for it also, showing clouds of electric charge above and below the plane of the ring. 

In addition to the supporting self-citations [742,6,457,330], there was much early support for the formation of donor-acceptor complexes. Radke and Praus-nitz [743] interpreted the extensive loadings of phenols even at very low concentrations, in comparison with lower uptakes of several aliphatic adsorbates, as evidence for specific interaction with the activated carbon surface. Barton and Harrison [744] studied the effect of graphite outgassing temperature on the heat of immersion of benzene and attributed a shallow minimum at ca. 800°C to the effect of CO desorption, thus implicitly supporting the donor-acceptor complex proposal in terms of a reduction in the interaction between the partial charge on the carbonyl carbon atom and the 7t-electron cloud of the benzene molecule. ... 

Polarizable hydrocarbons, such as short-chain arenes (benzene, isopropylbenzene), have been shown to be solubilized in quaternary ammonium solutions initially by absorption at the micelle-water interface, replacing water molecules that may have penetrated into the outer core of the micelle close to the polar heads, but solubilization of additional material is either deep in the palisade layer or located in the inner core of the micelle (Eriksson, 1965). The polarizability of the ji-electron cloud of the aromatic nucleus and its consequent ability to interact with the positively charged quaternary ammonium groups at the micelle-water interface may account for the initial adsorption of these hydrocarbons in that location. In POE nonionics, benzene may be solubilized between the polyoxyethylene chains of the hydrophilic groups (Nakagawa, 1967). 

The application of an electric field always causes some physical changes in the medium even if the liquid molecules are non-polar, the electrons in the molecule will be affected by the electric field. The movement of electrons within the molecule results in an induced dipole, ft, and the alignment of the induced dipoles with the electric field gives induced polarization. For example, if a positive charge is placed above the plane of a neutral benzene molecule, the average positions of the electrons will shift upward, giving the benzene molecule a dipole moment whose direction is perpendicular to the molecular plane. In summary, when a non-polar molecule is subjected to an electric field, the electrons in the molecule are displaced from their ordinary positions so that the electron clouds and nuclei are attracted in opposite directions and a dipole is induced thus the molecule temporarily has an induced dipole moment, ft. 

---