Relative reactivity determination

More quantitative results are available for the nitration of alkyl-thiazoles Dou et al. (373) determined the reactivity, relative to benzene, of the nitration site of various mono- and dialkylthiazole by competition experiments (Table 1-53). 

Relative reactivity of ring-positions based on positional selectivity of polychloro-azines must be regarded with caution because of the unequal activating effects of the chlorine substituents on each other. Also, it should be emphasized that one cannot use the positional selectivity in di- and tri-substitutions to assess relative reactivity of different positions. In such substitutions, the reactivity is determined by a complex combination of activating and deactivating effects which are unequal at the ring-positions (cf. Sections II, E, 1, II, E, 2,c, and II,E,2,e). 

The effect of f-BuX, Et2 A1X and MeX on PIB yield and polymerization rate was studied (Sections V, VI, VII). Relative initiator reactivities were determined based on yields, initiator efficiencies at —60 °C, polymerization rates and floor temperatures. Initiator reactivity orders can be summarized as follows ... 

Early this year, Middleton and Ingold (29) reported relative rates of chain propagation of a primary, secondary, and tertiary peroxy radical (from allylbenzene, Tetralin, and a-methylstyrene, respectively) with a series of nine hydrocarbons. By using a large excess of one of the first three hydrocarbons, they dealt almost entirely with one chain carrier in each co-oxidation. Relative reactivities were determined by a GLPC method like that of Russell and Williamson (31, 32). They concluded that the average relative reactivities of the primary, secondary, and tertiary peroxy radicals toward the nine hydrocarbons were 5.2/2.2/1.0 but that the relative reactivities of the nine hydrocarbons were about the same toward each type of radical. These results are acceptable as semi-quantitative. However, despite numerous replicate analyses, their experimental method suffers from the same limitations as that of Russell and Williamson, and they give no primary data—only the calculated results. 

Waack and Doran [26] reported on the relative reactivities of 13 structurally different organolithium compounds in polymerization with styrene in tetrahydro-furan at 20°C. The reactivities were determined by the molecular weights of the formed polystyrene. The molecular weights are inversely related to the activity of the respective organolithium polymerization initiators. Reactivities decreased in the order alkyl > benzyl > allyl > phenyl > vinyl > triphenylmethyl as shown in Table 3.1. 

The relative reactivities were determined by means of competition with different nucleophiles RYH and RY H. 

Recently the overall reactivities relative to the monocyclic rings have been determined for a number of reactions77 by kinetic or competitive procedures. The data, reported in Table XVIII, show that fusion with a benzene ring produces an overall decrease in reactivity in both systems. The decrease is much more pronounced for furan than for thiophene ring. As a consequence of this, the overall reactivities of benzofuran and benzothiophene are nearly equal in all the substitutions for which quantitative data are available (column 3 of Table XVIII for a useful comparison the relative reactivities of the monocyclic rings in the same reactions are also reported in column 4). 

Tertiary radical formation is more exothermic, yet more primary alkyl chloride is formed than tertiary alkyl chloride. However, once the 9 1 ratio of primary to tertiary hydrogen atoms is taken into account, the relative reactivities, as determined experimentally, turn out to be as shown in the table. 

Relative reactivities were determined by the method of initial rates and normalized to 35 C. "FOr pairs of compounds as indicated for the last eight entries, relative to PhC CPh = I. 

Gas-phase reactivity studies form the key issue in the research of the Berlin group. Note that relativity is not explicitly addressed here because reactivity is determined by thermochemical and kinetic aspects, and nonrelativistic considerations of reaction kinetics are almost meaningless (see also Section 7.4). Whereas bare Au+ shows... 

The trend of reactivity tert > sec > pri is consistently observed in various hydrogen atom abstraction reactions, but the range of reactivity is determined by the nature of the reacting radical. The relative reactivity of pri, sec, and tert positions toward hydrogen abstraction by methyl radicals is 1 4.8 61. An allylic or benzylic hydrogen is more reactive toward a methyl radical by a factor of about 9, compared to an unsubstituted C—H. The relative reactivity toward the t-butoxy radical is pri 1, sec 10, tert 50. In the gas phase, the bromine atom is much more selective, with relative reactivities of pri 1, sec 250, tert 6300. Data for other types of radicals have been obtained and tabulated. ... 

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