Compounds with Aromatic Rings

Compounds with carbon-carbon double bonds or aromatic rings give rise to chemical shifts in the range from 100 to 175 ppm. Since relatively few other peaks appear in this range, a great deal of useful information is available when peaks appear here. 

Difficult to assign without using chemical shift correlation tables 

In an off-resonance-decoupled or proton-coupled spectrum, a monosubstituted benzene ring shows three doublets and one singlet. The singlet arises from the ipso carbon, which has no attached hydrogen. Each of the other carbons in the ring ortho, meta, and para) has one attached hydrogen and yields a doublet. 

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Depending on the mode of substitution, a symmetrically disubstituted benzene ring can show two, three, or four peaks in the proton-decoupled spectrum. The following drawings illustrate this for the isomers of dichlorobenzene  

A carbon attached to a double bond is deshielded due to its sp hybridization and some diamagnetic anisotropy. This effect can be seen in the NMR spectrum of cyclohexene (Fig. 4.12). Cyclohexene has a plane of symmetry that runs perpendicular to the double bond. As a result, we observe only three absorption peaks. There are two of each type of carbon. Each of the double-bond carbons c has only one hydrogen, whereas each of the remaining carbons has two. As a result of a reduced NOE, the double-bond carbons have a lower-intensity peak in the spectrum. 

198 Nuclear Magnetic Resonance Spectroscopy Part Two Carbon-13 Spectra 

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The review of known integrase inhibitors presented in the previous section demonstrates the paucity of effective inhibitors reported in the literature. A limited number of structural types have been investigated, focused heavily on compounds with aromatic ring systems and hydroxy substituents. Most inhibitors reported to date are only moderately effective in in vitro assays, with IC50 values residing in the low p/Vfrange (see Table 1). 

Compounds that absorb around 254 nm, including most compounds with aromatic rings and conjugated double bonds and some unsaturated compounds, can be detected on an F layer containing a phosphor or... 

Metallocenes Sandwich compounds with aromatic rings bonded by 2/)7t-electrons to a metal atom or ion. The aromatic rings act as ligands. 

Compounds with aromatic rings, C=C double bonds, or with functional groups containing double bonds to some heteroatoms, particularly when these structures are multiply... 

The direct conversion of hydrocarbons to diamond has also been demonstrated. C3 is the region where organic compounds such as anthracene, camphene, fluorene, pyrene, sucrose, polyethylene, adamantane, and paraffin wax have been converted to very fine diamonds under high pressure (about 1pm in size) (Wentorf [33]). Aliphatic compounds seem to work but compounds with aromatic rings and/or... 

Compounds with aromatic rings occupy numerous and important positions in reactions that occur in living systems. It would be impossible to describe them all in this chapter. We shall, however, point out a few examples now and we shall see others later. 

Sandwich compounds with aromatic rings bonded by 2pK-... 

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