Spectroscopic features

The synthesis of aromatic hydrocarbons (arenes) is for convenience organised under the following five headings. 

Many convenient methods for the introduction of carbon-carbon double bonds into a saturated carbon chain involve the removal of two atoms or groups from adjacent carbon atoms. Usually, but not invariably, one of these groups is hydrogen (i.e. the removal of HX). Two main types of elimination reactions are recognised - heterolytic processes in solution and pyrolytic reactions in the gas phase. A detailed discussion of the mechanisms of these reactions may be found in all standard and advanced textbooks in each of the reactions discussed below the probable mechanism is noted in relation to the aim of obtaining good yields of regio- or stereoisomerically pure compounds. 

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The IR H NMR and NMR spectra of dipropyl ether which appear in parts a b and c respectively of Figure 16 8 illustrate some of the spectroscopic features of ethers... 

Although FeMo-cofactor is clearly knpHcated in substrate reduction cataly2ed by the Mo-nitrogenase, efforts to reduce substrates using the isolated FeMo-cofactor have been mosdy equivocal. Thus the FeMo-cofactor s polypeptide environment must play a critical role in substrate binding and reduction. Also, the different spectroscopic features of protein-bound vs isolated FeMo-cofactor clearly indicate a role for the polypeptide in electronically fine-tuning the substrate-reduction site. Site-directed amino acid substitution studies have been used to probe the possible effects of FeMo-cofactor s polypeptide environment on substrate reduction (163—169). Catalytic and spectroscopic consequences of such substitutions should provide information concerning the specific functions of individual amino acids located within the FeMo-cofactor environment (95,122,149). 

Although three different models were already proposed to explain the mechanism of adenylylsulfate reduction (141-143), a global model (taking in account the spectroscopic features discussed earlier) was not yet presented. In particular, the role of center II is still unknown. 

The difficulty is that characterization techniques are usually not selective towards active sites, so very often the main spectroscopic features are not evidence for active sites manifestations. However, it is possible to find some exceptions mainly among functionalized materials, such as zeolites. One of the few well established examples is TS-1 [7], a zeolite discovered in 1983 behaving as a catalyst for partial oxidation reactions in H2O2/H2O solutions [8-20]. 

While the general features of halogen bonding are now well known, it has proven challenging to develop models with sufficient accuracy to predict spectroscopic features and bond energies. This is particularly problematic with iodine, where high quality basis sets are not readily available and are computationally expensive. There have been numerous approaches taken to address this issue during the past decade, many of which are discussed below. 

If one of the compounds of interest has a unique spectroscopic feature, or can be synthesized with a fluorescent or radioactive label, then a variety of equilibrium... 

Table 1 Summary of the spectroscopic features of ligands 1-4 and their respective Pd and Pt complexes 5-12. aH1, aH2, pH1, pH2 are defined in the scheme given below (5 in ppm, J in Hz).

Rodgers, M.A.J. and Bates A.L. 1980. Kinetic and spectroscopic features of some carotenoid triplet states Sensitization by singlet oxygen. Photochem. Photobiol. 31 533-537. 

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