Benzene theoretical studies

The excited states of benzene exemplify the importance of the following points in any theoretical study of excited states ... 

We have previously in a number of papers [1-5] investigated these effects ft -both the Jahn-Teller inactive molecule n-butane [1] and the Jahn-Teller active molecules ethane, cyclopropane, and cyclohexane [2-5]. The choice of systems was largely dictated by the availability of experimental results [5-8]. New experiments being performed on selectively deuterated benzene have motivated a closer theoretical study of this system, and a first presentation of these investigations is given in the present paper. 

Allyl (27, 60, 119-125) and benzyl (26, 27, 60, 121, 125-133) radicals have been studied intensively. Other theoretical studies have concerned pentadienyl (60,124), triphenylmethyl-type radicals (27), odd polyenes and odd a,w-diphenylpolyenes (60), radicals of the benzyl and phenalenyl types (60), cyclohexadienyl and a-hydronaphthyl (134), radical ions of nonalternant hydrocarbons (11, 135), radical anions derived from nitroso- and nitrobenzene, benzonitrile, and four polycyanobenzenes (10), anilino and phenoxyl radicals (130), tetramethyl-p-phenylenediamine radical cation (56), tetracyanoquinodi-methane radical anion (62), perfluoro-2,l,3-benzoselenadiazole radical anion (136), 0-protonated neutral aromatic ketyl radicals (137), benzene cation (138), benzene anion (139-141), paracyclophane radical anion (141), sulfur-containing conjugated radicals (142), nitrogen-containing violenes (143), and p-semi-quinones (17, 144, 145). Some representative results are presented in Figure 12. 

Another type of interaction is the association of radical ions with the parent compounds. Recently (118), a theoretical study was reported on the interaction of butadiene ions with butadiene. Assuming a sandwich structure for the complex, the potential curve based on an extended Hiickel calculation for two approaching butadienes (B + B) revealed only repulsion, as expected, while the curves for B + and B + B" interactions exhibit shallow minima (.068 and. 048 eV) at an interplanar distance of about 3.4 A. From CNDO/2 calculations, adopting the parameter set of Wiberg (161), the dimer cation radical, BJ, appears to be. 132 eV more stable than the separate B and B species, whereas the separate B and B species are favored by. 116eV over the dimer anion radical, BJ. This finding is consistent with experimental results formation of the dimer cation radical was proved in a convincing manner (162) while the attempts to detect the dimer anion radical have been unsuccessful. With other hydrocarbons, the reported formation of benzene dimer anion radical (163) represents an exceptional case, while the dimeric cation radical was observed... 

Both benzene dimer ion radicals were a subject of a recent theoretical study (166). 

Stokbro K, Taylor J, Brandbyge M, Mozos JL, Ordejon P (2003) Theoretical study of the nonlinear conductance of di-thiol benzene coupled to Au(l-l-l) surfaces via thiol and thiolate bonds. Comput Mater Sci 27(1/2) 151-160... 

A theoretical study (144) and several experimental studies using selectively deuterated mono-substituted benzenes (145), chlorobenzene (146), and warfarin (147) (Fig. 4.79) provided strong evidence for the stepwise mechanism. Most recently, a theoretical study using density functional calculations reported the same basic conclusion (148). The reaction proceeds by a stepwise mechanism involving initial attack of FeO3"1" on the jt system to form a tetrahedral intermediate (pathway 2). The tetrahedral intermediate then goes... 

Experimental and theoretical studies of the basicity and acidity of benzene-substituted indoles were performed169. In aqueous solution, the pK values are above —4 for the bases and above 15 for the acids. Gas-phase ionization enthalpies have been calculated using the AMI semiempirical method. 

The syntheses and reactivities of fully conjugated rings for these kinds of compounds have not been reported in the available literature. However, the positional isomers of the 1,2-disubstituted benzenes have been theoretically studied using ab initio calculations at the HE, MP2, and CCSD(T) levels of theory and also by using the DFT theory <2000JA11173> and are discussed, together with the 1,3- and 1,4-positional isomers, in Chapter 8.11. 

Possibly the earliest theoretical study of diffusion of aromatics in zeolites was published in 1987 by Nowak et al. (89), who considered diffusion of benzene and toluene in the pores of silicalite and theta-1. Theta-1 (90) has a unidimensional medium-sized pore opening bounded by 10-rings. In this study, only the straight channel of silicalite was considered, making the... 

Although valence isomerization reactions of aromatic compounds have found little by the way of practical application, they are a fascinating area for mechanistic and theoretical study. The details are not completely dear, but it seems that, for benzene itself, benzvalene arises from the lowest excited singlet state, perhaps by way of a biradical intermediate (3.32) that could also be a precursor to fulvene bicyclohexadiene is probably produced from the second excited singlet state. For some other aromatic compounds the electronic nature of 5, and S2 may be reversed, or at least the states are much closer in energy, so that the preference for benzvalene or bicyclohexadiene formation under conditions of long-wavelength irradiation can be rationalized. 

Mulliken attributed the strong absorption band of the system to the excitation of the ground-state complex to the CT state with the aromatic molecule acting as the electron donor and the iodine as the acceptor, that is, Bz+ I2. Several spectroscopic and theoretical studies have predicted that the Bz I2 ground state has a C(,v axial structure with the 1—I bond being perpendicular to the benzene molecular plane. The heat of formation of this complex in the gas phase was determined by spectrometric methods to be on the order of 2-3 kcal/mol and our ab initio calculations support these values. 

Theoretical studies on thiepine-thianorcaradiene (benzene sulfide) valence isomerization have been of continuous interest. In addition, hypervalency of sulfur in thiepines has been theoretically studied. The interest in fused systems, such as dibenzo[/)/]thiepines, toward pharmacologically active compounds is growing. In the last decade, many reports on the synthesis, characterization, and utilization of enantiomerically pure dihydro- and tetrahydrothiepines and thiepanes have appeared. 

Nitrations of aromatic compounds represent one of the most important classes or organic reactions. However, although a lot of data has been collected in relation to simple substituted benzenes, and the reactions have been subjected to quantitative and theoretical studies, the nitration of phenyl heterocycles has been much less studied in a systematic way. This chapter has attempted to bring together as much information as possible on the topic through a manual search of Chemical Abstracts and recent literature. 

An interesting aspect of this problem is that posed by the Jahn-Teller effect in the benzene anion. These ions, together with the cations and anions of coronene (Bolton and Carrington, 1961c de Boer and Weissman, 1958), have spectra consisting of unusually broad lines which are very hard to saturate. Theoretical studies (McConnell, 1961 McConnell and McLachlan, 1961) suggest that the broadening is a result of spin-orbit interaction but the relaxation is linked to the dynamic Jahn-Teller effect. 

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