Aromatic ring parameter

I. Further work from Liu s group has involved B-strain and solvolytic reactivity revisited. Nucleophilic solvent participation and abnormal rate ratios for tertiary chloroalkanes. The abnormal rate ratios are those involving introducing FV, and are considered due to competition between B strain and nucleophilic solvent participation. In presenting solvolytic studies of 4-methoxybenzyl chloride and bromide, and of l-(4-methoxyphenyl)ethyl chloride, further opportunity was taken to criticize the introduction and use of the aromatic ring parameter /. ... 

The solvolyses of p-methoxybenzyl chloride in 39 solvents are well correlated by an extended Grunwald-Winstein equation involving terms in Tci (solvent ionizing power), At (solvent nucleophilicity) and I (Kevill s aromatic ring parameter). A claim by Liu that nucleophilic participation is greater than in the solvolyses of the corresponding bromide is discussed and said to be disproved. 

The parameter giving the ratio of the number of substitutable aromatic carbon atoms to the total number of aromatic carbons which gives a measure of the average condensation of aromatic rings. 

In order for the transferability of parameters to be a good description of the molecule, force fields use atom types. This means that a sp carbon will be described by different parameters than a. sp - carbon, and so on. Usually, atoms in aromatic rings are treated differently from sp atoms. Some force fields even parameterize atoms for specific functional groups. For example, the carbonyl oxygen in a carboxylic acid may be described by different parameters than the carbonyl oxygen in a ketone. 

The Fischer cyclization has proved to be a very versatile reaction which can tolerate a variety of substituents at the 2- and 3-positions and on the aromatic ring. An extensive review and compilation of examples was published several years ago[3]. From a practical point of view, the crucial reaction parameter is often the choice of the appropriate reaction medium. For hydrazones of unsymmetrical ketones, which can lead to two regioisomeric products, the choice of reaction conditions may determine the product composition. 

Compared with the bonding groups (mol%) to aromatic ring of PS, the degree of acylation was observed when MA was used. These results was obtained by determination of kinetic parameters of PS with MA and AA under the same reaction conditions. As shown in Table 5, if the initial rate (Wo) and rate constant (K) of the acylation reaction between MA and AA are compared, the MA is almost 10-14 times higher than AA in the presence of BF3-OEt2 catalyst. This fact is due to the stretching structure of MA and the effect of the catalyst. 

Finaiiy, carbon chains that have an unsaturated bond, an aromatic ring or another group, can cause dangerous reactions which involve these structural elements or groups. In this case, the simultaneous presence of these structural parameters can boost their reactivity due to the electronic effects that they exert on each other. 

An EPR study of the monomeric 02 adducts of the Schiff base complexes of Co(bzacen)(py) (71a) and the thiobenzoyl analog Co(Sbzacen)(py) (71b) characterized the five-coordinate mono (pyridine) precursors and the six-coordinate 02 adducts.327 Increased covalency in the Co—S bonds was seen in the EPR parameters, indicative of 7r-backbonding. Substituent effects on the aromatic rings had no effect on the EPR spectra, but these were reflected in the observed redox potentials. Furthermore, the S-donors stabilize the Co ion in lower oxidation states, which was consistent with destabilization of the 02 adducts. 

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