Charge separation

Tropone, 1 (a), and azulene, II (a), shown in Fig. 4 have resonance energies, of 12 and 28 kcal/mole, respectively. The theoretical implication of a stable system being achieved by six r-electrons, is that the structures are closer to those shown in I (6) and II (5) certainly this is in keeping with the observed physical and chemical properties. 

In both of these cases a certain amount of energy is expended, relative to the classical structures, in separation of the charges. Hence the true resonance energies will be increased by this amount from the figures calculated either by bond energies or from heats of hydrogenation. 

Likewise, in the reference compound, which in this case is cyclohexene, the heat of hydrogenation, also includes a term, 

HuckeFs rule leads one to expect resonance stabilization in the cyclopentadienate and cycloheptatrienyl (tropyllum) ions. With a view to determining the resonance energy of the latter, Turner has measured the heat of hydrogenation of tropylium chloride to cycloheptaiie and hj drogen chloride, in acetic acid solution, ag — 86 23 rt 0 08 kcal/mole. An energetic comparison of the relative stabilities of tropylium chloride and the isomeric benzyl chloride 

The heats of formation of liquid cycloheptane ( -37-7kcal/ mole) and of gaseous hydrogen chloride (—22-1 kcal/mole) can be used in conjunction with their respective heats of solution in acetic 

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Derive the expression for the electric field around a point dipole, Eq. VI-5, by treating the dipole as two charges separated by a distance d, then moving to distances X d. 

Kirmaier C and Holten D 1988 Subpicosecond spectroscopy of charge separation in Rhodobacter capsulatus reaction centers Isr. J. Chem. 28 79-85... 

Holzapfel W, Finkele U, Kaiser W, Oesterhelt D, Scheer H, Stilz H U and Zinth W 1989 Observation of a bacteriochlorophyll anion radical during the primary charge separation in a reaction center Chem. Rhys. Lett. 160 1-7... 

Triton X-100 and y-cyclodextrin, and subsequent charge separation via reductive quenching Chem. Phys. Lett. 223 511-16... 

Williams R M, Koeberg M, Lawson J M, An Y-Z, Rubin Y, Paddon-Row M N and Verhoeven J W 1996 Photoinduced electron transfer to Cgg across extended 3- and 11 a-bond hydrocarbon bridges creation of a long-lived charge-separated state J. Org. Chem. 61 5055-62... 

Bell TDM, Smith T A, Ghiggino K P, Ranasinghe M G, Shephard M J and Paddon-Row M N 1997 Long-lived photoinduced charge separation in a bridged Cgg-porphyrin dyad Chem. Phys. Lett. 268 223-8... 

Liddell P A, Kuciauskas D, Sumida J P, Nash B, Nguyen D, Moore A L, Moore T A and Gust D 1997 Photoinduced charge separation and charge recombination to a triplet state in a carotene-porphyrin-fullerene triad J. Am. Chem. Soc. 119 1400-5... 

The various fonns of betaines are very important for their charge control functions in diverse applications and include alkylbetaines, amidoalkylbetaines and heterocyclic betaines such as imidazolium betaines. Some surfactants can only be represented as resonance fonns having fonnal charge separation, although the actual atoms bearing the fonnal charge are not ftmctionally ionizable. Such species are mesoionic and an example of a trizaolium thiolate is illustrated in table C2.3.3. 

Charge separation Bohr electron 1 Bohr electron = 2.541765 Debye... 

QM/MM methods do not allow for charge transfer between different regions of the system. Thus, partitioning should not divide sections expected to have a charge separation. 

The Poisson equation assumes that the solvent is completely homogeneous. However, a solvent can have a significant amount of charge separation. An example of a heterogeneous solution would be a polar solute molecule surrounded by water with NaCl in solution. The positive sodium and negative... 

The Poisson-Boltzmann equation is a modification of the Poisson equation. It has an additional term describing the solvent charge separation and can also be viewed mathematically as a generalization of Debye-Huckel theory. 

The carbonyl group withdraws rr electron density from the double bond and both the carbonyl carbon and the p carbon are positively polarized Their greater degree of charge separation makes the dipole moments of a p unsaturated carbonyl compounds signifi cantly larger than those of comparable aldehydes and ketones... 

However, not all excitons have sufficiently long lifetimes to reach the interface before recombining. To circumvent this problem and increase device efficiency, heterostmcture devices have been fabricated. In these devices, donors and acceptors are mixed together to create a network that provides many internal interfaces where charge separation can occur. Heterostmcture devices made from the donor polymer... 

An electric dipole consists of two equal and opposite charges separated by a distance. AH molecules contain atoms composed of positively charged nuclei and negatively charged electrons. When a molecule is placed in an electric field between two charged plates, the field attracts the positive nuclei toward the negative plate and the electrons toward the positive plate. This electrical distortion, or polarization of the molecule, creates an electric dipole. When the field is removed, the distortion disappears, and the molecule reverts to its original condition. This electrical distortion of the molecule is caHed induced polarization the dipole formed is an induced dipole. 

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