Nuclear energy aromatic

In addition to the above prescriptions, many other quantities such as solution phase ionization potentials (IPs) [15], nuclear magnetic resonance (NMR) chemical shifts and IR absorption frequencies [16-18], charge decompositions [19], lowest unoccupied molecular orbital (LUMO) energies [20-23], IPs [24], redox potentials [25], high-performance liquid chromatography (HPLC) [26], solid-state syntheses [27], Ke values [28], isoelectrophilic windows [29], and the harmonic oscillator models of the aromaticity (HOMA) index [30], have been proposed in the literature to understand the electrophilic and nucleophilic characteristics of chemical systems. 

A simple diagram depicting the differences between these two complementary theories is shown in Fig. 1, which represents reactions at zero driving force. Thus, the activation energy corresponds to the intrinsic barrier. Marcus theory assumes a harmonic potential for reactants and products and, in its simplest form, assumes that the reactant and product surfaces have the same curvature (Fig. la). In his derivation of the dissociative ET theory, Saveant assumed that the reactants should be described by a Morse potential and that the products should simply be the dissociative part of this potential (Fig. Ib). Some concerns about the latter condition have been raised. " On the other hand, comparison of experimental data pertaining to alkyl halides and peroxides (Section 3) with equations (7) and (8) seems to indicate that the simple model proposed by Saveant for the nuclear factor of the ET rate constant expression satisfactorily describes concerted dissociative reductions in the condensed phase. A similar treatment was used by Wentworth and coworkers to describe dissociative electron attachment to aromatic and alkyl halides in the gas phase. ... 

In a 7r electron system the orbitals of an aromatic positive ion are similar to the corresponding orbitals of the neutral molecule. In contrast, in small molecules electronic rearrangement following excitation is often sufficiently important that changes in nuclear geometry, correlation energy, etc., are all essential to the correct interpretation of the excitation phenomenon. Because of the similarity in the orbital systems of neutral and positive ion aromatic compounds, we shall assume that it is possible to describe the photoionization of an aromatic molecule within the framework of a one-electron model. Given that the n and a electrons are describ-able by a set of separable equations of motion, we need consider only the initial and final orbitals of the most weakly bound electron to determine the ionization cross section near to the threshold of ionization. 

In the context of the direct mechanism, several perplexing features concerning nuclear and side-chain substitution of aromatic compounds have been highlighted [124-126], and in the search for explanations attempts have been made to estimate, by thermo-chemically based calculations, free energies of activation for reactions between radical cations and nucleophiles. Long-standing puzzles in this area include the dependence of the ratio of side chain/nuclear substituted products on the nucleophile for alkylbenzenes, side-chain acetoxylation predominates in acetic acid (AcOH) unless AcO is present, when nuclear substitution becomes important. 

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