Aromatic adjacent hydrogen

Aliphatic stretching, FTIR of vitrinite, 103-12 Alkyl phenols, Py-MS, 153f Analytical analyses of demineralized coals, density fractions, 71t Aromatic adjacent hydrogen in... 

In this instance a second aromatic ring can be substituted for two adjacent hydrogen atoms giving condensed polynuclear aromatics, for... 

Or by a naphthenic ring which can also be substituted for two adjacent hydrogen atoms forming a naphthene aromatic such as tetralin or tetra.hydronaphthaiLene. ... 

As described in Section IV.B, dibenzothiophenes, when substituted in positions adjacent to the sulfur atom, have reduced activity for direct sulfur extraction. As a result, catalysts that promote aromatic ring hydrogenation offer another route to desulfurization, as the partially hydrogenated ring presents much less steric restrictions to adsorption via r -S type bonding (17,21) or to oxidative addition to form a metallathiabenzene intermediate, as discussed in Section IV.E.3. In addition, the metal-S coordination bond strength is increased by increasing the electron density on sulfur, and the C-S bonds in hydrothiophenes are much weaker. 

Figure 5. Spectral area for aromatic 1 adjacent hydrogen at 884 crrrl (curve fitting) vs. reflectance.

Certain aliphatic and aromatic bands are interdependent, and therefore redundant, in principal components analyses. These are (a) aliphatic CH3 at 2956 cm-1 and aliphatic CH at 2891 cm-1, and (b) aromatic one, two, three, and four adjacent hydrogens at 884, 815, 801, and 750 cm"l, respectively, and total aromatic content. It is only necessary, then, to obtain data for one component from each of these two groups for study. 

In the spectra of a-substituted naphthalenes, the bands for the isolated hydrogen and the two adjacent hydrogen atoms of /3-naphthalenes are replaced by a band for three adjacent hydrogen atoms. This band is near 810-785 cm 1. Additional bands may appear because of ring bending vibrations (see Table 2.3). The position of absorption bands for more highly substituted naphthalenes and other polynuclear aromatics are summarized by Colthup et al. (1990) and by Conley (1972). 

The spectrum of one of the SMA copolymers investigated (Figure 2) is also consistent with that of published spectra (33). The strong absorption band at approximately 706 - 764 cm"l are indicative of aromatic rings containing five adjacent hydrogen atoms, while the absorption bands at 1780 and 1860 cm l are consistent with those of a saturated five membered cyclic anhydride. The two shoulders on the 1780 cm" peak possibly indicate some hydrolysis as the result of processing. 

The McConnell equation (Equation 1.18) expresses the relationship of the observed coupling constant (an) to the unpaired spin population on the adjacent carbon atom (pc) The constant Q is different from one situation to another, but when an electron in a pz orbital on a trigonal carbon atom couples to an adjacent hydrogen, it is about -24 G. Applied to aromatic hydrocarbons, where it is particularly easy to generate radical cations and anions, there proves to be a good correlation between coupling constants and the calculated coefficients in the HOMO and LUMO, respectively.62... 

Arynes and heteroarynes are reactive intermediates derived formally by the removal of two adjacent hydrogens from, respectively, a carbocyclic or a heterocyclic aromatic ring. Prototypical examples are benzyne (1) and 3,4-didehydropyridine (2). Since these molecules contain a partial triple bond, they are properly regarded as -ynes and, as will be seen, undergo many reactions typical of that functionality, modified by the inherent strain caused by their nonlinearity. 

Aromatic compounds have two characteristic types of hydrogens aromatic ring hydrogens (benzene ring hydrogens) and benzylic hydrogens (those attached to an adjacent carbon atom). 

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