Single aromaticity

In this book, we will use a circle to represent single aromatic rings (as, e.g., in 32), but will show one canonical form for fused ring compounds (e.g., 36). It would be... 

As will be noted from even a cursory look at the structures of the two acylation products shown in Scheme 1, there is but a single aromatic methine resonance, that, regardless of which substitution product... 

A single aromatic nucleus is not usually sufficient to stabilize an oxygen free radical, but the radical derived from 2,4,6-tritertiary-butylphenol is protected from dimerization or attack on the nucleus... 

We can then say that planar cyclooctatetraene is antiaromatic because two antiaromatic unions dominate a single aromatic union. Alternatively, we can say that cyclooctatetraene is antiaromatic because the crucial union, Le. the union involving the greatest spatial overlap, is the (A + B + C) + D union which is antiaromatic. 

J. B. A. Ross, W. R. Laws, J. C. Sutherland, A. Buku, P. G. Katsoyannis, I. L. Schwartz, and H. R. Wyssbrod, Linked-function analysis of fluorescence decay kinetics Resolution of side-chain rotamer populations of a single aromatic amino acid in small polypeptides, Photochem. Photobiol. 44, 365-370 (1986). 

Among the polynuclear aromatic hydrocarbons, the toxicity of petroleum is a function of its di- and triaromatic hydrocarbon content. Like the single aromatic... 

The helix contents of five peptide fragments from the protein thermolysin have been determined by CD and NMR in both water and 30% TFE. 85 The helix content was obtained from CD by the method of Chen et a I.162 and the NMR method utilized chemical shifts. 84 Four of the five peptides correspond to helical regions in the intact protein, and one corresponds to an Q-loop. 86 The rms difference between CD and NMR helix contents for the five peptides under the two conditions is 7.5%. One peptide shows the largest deviations (0 vs 13% in water, 45 vs 62% in 30% TFE). If it is excluded, the rms deviation decreases to 4%. The peptide showing the largest deviation, residues 258-276 from the thermolysin sequence, has two Tyr and one Phe (with the Phe adjacent to one of the Tyr in the sequence), and therefore it has an above-average content of aromatic amino acids, which can perturb both the CD spectrum and NMR chemical shifts. Of the other four peptides, three have a single aromatic residue and the fourth has two aromatics. 

Vallee reported another example of a BINOL-based Lewis acid catalyst for the asymmetric Strecker reaction of ketoimines. While a traditional (BINOL)Ti(IV)-based system provided poor enantioselectivity [61], Sc(BINOL)2Li proved to be highly enantioselective for the cyanation of N-benzyl acetophenonimine (95% ee at 50% conversion, 91% ee at 80% conversion) [62], Unfortunately, results were provided only for a single ketoimine and a single aromatic aldimine, leaving the generality of the methodology in question. 

Beside these compounds which combine alkyl chains and perfluorinated chains at opposite ends of a cyclic unit, there are several examples of liquid crystalline materials combining a single aromatic ring with a single semiperfluorinated alkyl chain or with two or three Rp-chains in close proximity. 

Polymers with fluorinated segments represent a field on its own which is not considered here [382-384], Polymer chains were also used to interconnect fluorous mesogenic units, either comprising a single aromatic unit [385-389] or a rod-like units which can be attached either terminally [193, 390-394] or laterally [240, 395-397] to the polymer backbone. In most cases the termini of the mesogenic units... 

In the first case [1] Y can be either a hydroxy, alkoxy or nitro group. The first two groups are important but variable constituents in coals and the last is probably minor or non-existent. The second active class of species are the alkyl-pyridines [2]. The final case [3] includes substituents on the benzyl carbon where X can be an ether or carbonyl functional group. The general mechanism of this reaction is most probably the base catalyzed iodination of the benzyl carbon with subsequent displacement of the iodide by the pyridine to form the pyridinium salt. In all three modes of activation, the single aromatic ring can be replaced with polycyclic rings. 

Extractive distillation, that is, fractional distillation in the presence of a solvent, is used to recover aromatic hydrocarbons from, say, reformate fractions in the following manner. By means of preliminary distillation in a 65-tray prefractionator, a fraction containing a single aromatic can be separated from the reformate, and this aromatic concentrate is then pumped to an extraction distillation tower near the top, and aromatic concentrate enters near the bottom. A reboiler in the extractive distillation tower induces the aromatic concentrate to ascend the tower, where it contacts the descending solvent. 

A. Linear unbranched condensation polymers containing CH2 groups and single aromatic rings1... 

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