Reactivity experimental

Free-radical reactivity of thiazole has been calculated by semiempirical methods, and results free valence and localization energy) have been compared with experimental data. For mono- and dimethylthiazoles the radical localization energy of the unsubstituted position may be correlated with the logarithm of experimental reactivity (180, 200). The value of the slope shows that a Wheland-type complex is involved in the transition state. 

Alfrey assigned styrene an e value of-1.0, but this was revised to the present value, which gives better agreement with experimental reactivity ratios. 

Experimental reactivity patterns are based on solution behavior which are influenced by interactions between solvent and reacting molecules (especially ions). Compare electrostatic potential maps of 2-methyl-2-propyl cation and dimethylhydroxy cation. Identify sites that might form strong hydrogen bonds with water. Which ion will be better stabilized by its interaction with water ... 

Chart 1. Experimental reactivity diagrams from piperidino-dehalogenation. Rates relative to a given position (= 1). Reactions in piperidine, structures 25-28 in alcohol, structures 29-31. Data deduced from refs. 18, 20, 29, 42, 43 and 98. 

In a study of quantum chemical calculations of reactivity, it was found that charge densities give only qualitative agreement with experimental reactivities in electrophilic substitution, whereas semiquantitative agreement is obtained with the localization energies.7... 

Fig. 4. Experimental reactivation energies for each donor element versus hydrogen-donor species bond strength. The formation of hydrogen-donor bonds is supported by the good correlation between these two parameters (Pearton et al., 1986).

The chiral sites which are able to rationalize the isospecific polymerization of 1-alkenes are also able, in the framework of the mechanism of the chiral orientation of the growing polymer chain, to account for the stereoselective behavior observed for chiral alkenes in the presence of isospecific heterogeneous catalysts.104 In particular, the model proved able to explain the experimental results relative to the first insertion of a chiral alkene into an initial Ti-methyl bond,105 that is, the absence of discrimination between si and re monomer enantiofaces and the presence of diastereoselectivity [preference for S(R) enantiomer upon si (re) insertion]. Upon si (re) coordination of the two enantiomers of 3-methyl-l-pentene to the octahedral model site, it was calculated that low-energy minima only occur when the conformation relative to the single C-C bond adjacent to the double bond, referred to the hydrogen atom bonded to the tertiary carbon atom, is nearly anticlinal minus, A- (anticlinal plus, A+). Thus one can postulate the reactivity only of the A- conformations upon si coordination and of the A+ conformations upon re coordination (Figure 1.16). In other words, upon si coordination, only the synperiplanar methyl conformation would be accessible to the S enantiomer and only the (less populated) synperiplanar ethyl conformation to the R enantiomer this would favor the si attack of the S enantiomer with respect to the same attack of the R enantiomer, independent of the chirality of the catalytic site. This result is in agreement with a previous hypothesis of Zambelli and co-workers based only on the experimental reactivity ratios of the different faces of C-3-branched 1-alkenes.105... 

Determination of (dn/dt)r is possible, since dO/dr)r can be found from the slope of the 0 vs. r plot and b can be found from the experimental reactivity curve. It should be noted that dn/di)r is the rate of reaction per cm. thickness of section, whereas the actual rate of reaction in an infinitesimal section of thickness dr is (dn/dt)r dr. 

Table I. Experimental Reactivity Ratios between Acrylated Lignin Model Compounds and MMA and S...

As for radical substitutions in compounds XV, XVII, XXV, and some other compounds, the F values (hence also Ar and Sr values, cf. section V, A) correctly predict the experimental reactivity order. The calculated and experimental orders disagree in the case of compounds XXI and, particularly, XVI the latter case (radical phenylation of quinoline) represents a serious failure of the theory, for the experimental study was very thorough.160 It is worth noting that in the compounds which have no meso-position the center of radical reactivity is the position adjacent to the nitrogen atom (with the exception of the just mentioned phenylation of quinoline). 

Experimental reactivity and mechanistic studies on the solvolysis of /3-sultams have shown that opening of the S-N bond produced a sulfonic acid or sulfonate ester and that there was no evidence of C-S fission. Alcoholysis of A-methyl-1,2-thiazetidine 1,1-dioxide 11 was investigated using ab initio calculations and density functional theory... 

Quantum-mechanical calculations have been successfully applied to the study of the carcinogenic pathways of PAH and aza-PAH derivatives, and very good correlations have been shown with the available experimental reactivities of these compounds (23-28). Furthermore, modeling studies of biological electrophiles from PAHs by density functional theory (DFT) methods have given proper descriptions of the charge delocalization modes and NMR characteristics of their resulting carbocations (29-33). 

Experimental reactivity ratios provide values for (QilQz) and ei — C ) for a given comonomer pair. In order to obtain numerical values of the four Q and e parameters from two reactivity ratios, two of the former are assigned arbitrary values. Originally, the scheme was anchored by selecting styrene as the reference monomer with 0 = 1.0 and e — —0.8. Later modifications have broadened the calculation base to include styrene copolymerization data of other well-researched monomers [26]. 

The Q-e numbers are obtained by fitting to experimental reactivity ratios, many of which are not very accurate. It is not surprising, then, that this prediction scheme is not quantitatively reliable. It is nevertheless very simple and convenient to use and it is at least qualitatively reasonable. Monomers with very different e values will evidently react with higher absolute values of (e — 2) values (Eq. 7-71). They will also be more likely to be influeneed in their behavior by... 

Fig. 4A and 4B Experimental reactivity of various treated charcoals, as a fimction of the conversion degree. The dashed lines are model fits. Fig. 4C Experimentally derived correction factors to the specific reaction rate constant Ks (see text).

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