Theoretical studies anilines

It is a well established fact that the preferred site of protonation of aniline in solution is the nitrogen atom, due to the higher stabilization upon solvatation of the N-protonated species with respect to the ring protonated ion (/). In the gas phase however, the situation is less clear, and the preferred site of protonation has been the subject of many experimental and theoretical studies. Based on proton transfer equilibria at 600 K and upon correlation of the proton affinities... 

G. Ciric-Marjanovic, M. Trchova, and J. Stejskal, Theoretical study of the oxidative polymerization of aniline with peroxydisulfate Tetramer formation, Int. J. Quantum Chem., 108, 318-333 (2008). 

Theoretical Studies in Photophysics and Photochemistry Applications to Aniline and Pyrazine... 

In Chap. 2, we have seen that the theoretical study of a molecular system is, in a vast majority of cases, separated in two steps. In a first step, the electronic structure of the system is studied by solving the electronic Schrodinger equation with fixed nuclei. This approach, combined with geometry optimization techniques, allows one to locate the important features of the various potential energy surfaces (PESs) of the electronic states of interest. In the context of photochemistry, as seen in Chap. 3, this approach allows one to characterize the various decay pathways of the molecule after photoexcitation. This information can then be used to interpret the various decay time constants obtained from time-resolved spectroscopic measurements. However, in most cases, including aniline studied in Chap. 3, various decay mechanisms are in competition, and it is often difficult to infer, from this static information, the relative importance of the various decay mechanisms. It is thus often necessary to study the dynamics of the nuclei in the manifold of the excited states of interest to obtain a deeper insight into the photophysics and photochemistry of the system of interest. 

Amunugama, R. and Rodgers, M.T. (2003) Influence of substituents on cation-jr interactions. 3. Absolute binding energies of alkali metal cation-aniline complexes determined by threshold collision-induced dissociation and theoretical studies. Int. J. Mass Spectrom. Ion Processes, 227, 339-360. 

The following discussion begins by presenting an in-depth view of the mechanism for the photochemical reduction of benzophenone by N, iV-dimethyl-aniline. This discussion is followed by a presentation of the theoretical models describing the parameters controlling the dynamics of proton-transfer processes. A survey of our experimental studies is then presented, followed by a discussion of these results within the context of other proton-transfer studies. 

In recent years, there have been many significant advances in our models for the dynamics for proton transfer. However, only a limited number of experimental studies have served to probe the validity of these models for bimolecular systems. The proton-transfer process within the benzophenone-AL A -di methyl aniline contact radical IP appears to be the first molecular system that clearly illustrates non-adiabatic proton transfer at ambient temperatures in the condensed phase. The studies of Pines and Fleming on napthol photoacids-carboxylic base pairs appear to provide evidence for adiabatic proton transfer. Clearly, from an experimental perspective, the examination of the predictions of the various theoretical models is still in the very early stages of development. 

Another common approach consists of the comparison between the experimental rate constants and theoretical values calculated by the procedure developed by Marcus (1956), Marcus and Sutin (1985) as well as Hush (1958). This classical procedure is used widely. Premsingh et al. (2004) gave the relevant references and described a detailed procedure to analyze the ion-radical reaction between anilines and chromium (V) complexes of azomethyne derivatives. Lepage et al. (2003) studied transformation of para-substituted thioanisoles to corresponding methylarylsulfoxides... 

Lutski directed attention to the H bond in simpler molecules by proposing that the influence of ethanol solvent on the UV spectrum of an orthoh.y6.voxy keto- or nitro aromatic provides a criterion for an j n/ramolecular H bond (1287, 1285). Brieglieb and Strohmeier were able to detect the influence of H bonded dimer formation on the spectra of acetic acid vapor at different temperatures (near 2100 A) (279). There have followed many valuable studies directed at the effect of H bonding on the electronic transitions of acids such as phenols, aniline (1483, 1481, 2056), benzoic acid and derivatives (2076, 1998, 671, 190), acetanilides (2075, 2074), HF (1771, 1770), naphthols (1479, 1484), sulfinic acids (521), and amides (1436). The most extensive work, that of Nagakura, Baba, and co-workers, is of particular importance because it led to theoretical consideration of the nature of the H bond (see Section 8.3.2). (See adso 2056,. 1418, 1850.)... 

Also, recent developments in quantum theoretical calculations of NMR parameters have increased their reliability and usefulness, especially in studying the dynamic processes such as conformational equilibria and tautomerism of aniline derivatives. All the above-mentioned items will be included in the following discussion. However, owing to the huge amount of data about H NMR parameters, the main focus of this review is directed to 13C, 15N and 19F NMR spectral studies of aniline derivatives. Schiff bases are not included in this review although some of them show an amino-imino tautomerism and can thus be considered as anilines. One reason for this is that a search in Chemical Abstracts using key words schiff base and nmr produced more than 1000 hits. 

To conclude, we point out that aniline and its numerous derivatives still offer challenges for both experimental and theoretical NMR studies. Especially in the area of solid state NMR, the determination of the components of anisotropic 15N shielding tensors and their quantum chemical calculations can give valuable information on the polymorphism and interactions of aniline derivatives in the solid state. 

Extensive attention is devoted to the interactions between aniline and aniline cation and neutral partners to form clusters which are investigated by recent techniques. In particular, van der Waals complexes between aniline and Ar, Kr, N2, CO, in both neutral and cationic forms, are studied by the technique of zero kinetic energy photoelectronic spectroscopy174. Theoretical studies175 on the aniline and aniline cation, free or complexed with a number of partners (as potential solvents) produce important results about the cluster geometry and the relative importance of different kinds of interactions. 

Pump-probe experiment is an efficient approach to detect the ultrafast processes of molecules, clusters, and dense media. The dynamics of population and coherence of the system can be theoretically described using density matrix method. In this chapter, for ultrafast processes, we choose to investigate the effect of conical intersection (Cl) on internal conversion (IC) and the theory and numerical calculations of intramolecular vibrational relaxation (IVR). Since the 1970s, the theories of vibrational relaxation have been widely studied [1-7], Until recently, the quantum chemical calculations of anharmonic coefficients of potential-energy surfaces (PESs) have become available [8-10]. In this chapter, we shall use the water dimer (H20)2 and aniline as examples to demonstrate how to apply the adiabatic approximation to calculate the rates of vibrational relaxation. 

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