1-Propyl radical

Heberger K and Fischer H 1993 Rate constants for the addition of the 2-cyano-2-propyl radical to alkenes in solution Int. J. Chem. Kin. 25 249-63... 

Because the starting material (propane) and one of the products (H ) are the same m both processes the difference m bond dissociation energies is equal to the energy dif ference between an n propyl radical (primary) and an isopropyl radical (secondary) As depicted m Figure 4 20 the secondary radical is 13 kJ/mol (3 kcal/mol) more stable than the primary radical... 

Alkyl radicals produced by oxidative decarboxylation of carboxylic acids are nucleophilic and attack protonated azoles at the most electron-deficient sites. Thus imidazole and 1-alkylimidazoles are alkylated exclusively at the 2-position (80AHC(27)241). Similarly, thiazoles are attacked in acidic media by methyl and propyl radicals to give 2-substituted derivatives in moderate yields, with smaller amounts of 5-substitution. These reactions have been reviewed (74AHC(i6)123) the mechanism involves an intermediate cr-complex. 

Simple alkyl radicals such as methyl are considered to be nonnucleophilic. Methyl radicals are somewhat more reactive toward alkenes bearing electron-withdrawing substituents than towards those with electron-releasing substituents. However, much of this effect can be attributed to the stabilizing effect that these substiments have on the product radical. There is a strong correlation of reaction rate with the overall exothermicity of the reaction. Hydroxymethyl and 2-hydroxy-2-propyl radicals show nucleophilic character. The hydroxymethyl radical shows a slightly enhanced reactivity toward acrylonitrile and acrolein, but a sharply decreased reactivity toward ethyl vinyl ether. Table 12.9 gives some of the reactivity data. 

Repeat your analysis for 2-methyl-2-propyl radical and 2-methyl-2-propyl anion, and assign preferred equilibrium geometry and the energy required to distort (by 10°) away from this geometry to each. 

Add the energies of propane and fluorine atom (at left (the reactants), and then the energies of 1-propyl radica (or 2-propyl radical) and hydrogen fluoride (th( products). Are these reactions exothermic or endothermic If the former, then calculate the relative concentrations 0 1-propyl radical and 2-propyl radical that would exist ii an equilibrium mixture at 298 K. Use equation (1). 

Radical stability can often be explained in the same way as ion stability molecules that delocalize unpaired electrons tend to be more stable. Display spin density surfaces for 1-propyl and 2-propyl radicals. In which is the unpaired electron more delocalized Is this also the lower-energy radical ... 

Use of the Hammond Postulate requires that the reverse reactions both be fast. Obtain energies for the transition states leading to 1-propyl and 2-propyl radicals ipropane+Br end and propane+Br center), and draw a reaction energy diagram for each (place the diagrams on the same axes). Is use of the Hammond Postulate justified Compare the partial CH and HBr bond distances in each transition state to the corresponding distances in propane and hydrogen bromide, respectively. Does the Hammond Postulate correctly predict which bond distances will be most similar Explain. 

Spin density surface for 2-propyl radical shows location of unpaired electron. 

First examine the geometry of methyl radical. Is it planar or puckered Examine the geometries of 2-methy 1-2-propyl radical, trifluoromethyl radical, trichloromethyl radical and tricyanomethyl radical. Classify each of the substituents (methyl, fluoro, chloro and cyano) as a n-electron donor or as a Tt-electron acceptor (relative to hydrogen). Does replacement of the hydrogens by 7t-donor groups make the radical center more or less puckered Does replacement by Jt-acceptor groups make the radical center more or less puckered Justify your observations. 

Examine spin density surfaces for l-bromo-2-propyl radical and 2-bromo-l-propyl radical (resulting from bromine atom addition to propene). Eor which is the unpaired electron more delocalized Compare energies for the two radicals. Is the more delocalized radical also the lower-energy radical Could this result have been anticipated using resonance arguments ... 

Affinities toward other alkyl radicals have also been measured by Szwarc and his co-workers using techniques similar to those described above, It is interesting to compare the affinities of naphthalene with those of quinoline toward methyl, ethyl, and n-propyl radicals (Table X). 

On the basis of the reaction of alkyl radicals with a number of polycyclic aromatics, Szwarc and Binks calculated the relative selectivities of several radicals methyl, 1 (by definition) ethyl, 1.0 n-propyl, 1.0 trichloromethyl, 1.8. The relative reactivities of the three alkyl radicals toward aromatics therefore appears to be the same. On the other hand, quinoline (the only heterocyclic compound so far examined in reactions with alkyl radicals other than methyl) shows a steady increase in its reactivity toward methyl, ethyl, and n-propyl radicals. This would suggest that the nucleophilic character of the alkyl radicals increases in the order Me < Et < n-Pr, and that the selectivity of the radical as defined by Szwarc is not necessarily a measure of its polar character. 

The self-reactions of 2-carboalkoxy-2-propyl radicals (8-10) have been examined.89 Ia> 104 The results of these studies are reported in Table 5.3. Combination is slightly favored over disproportionation. The value of kjkw for 8 was found to be essentially independent of temperature. 

Experimental studies on models of the propagating radicals in S-AN copolymerization32,33 and a few other systems34 provide support for an explicit penultimate unit effect. Of particular interest is the data of Tirrcll and coworkers. They investigated the relative reactivity of S and AN towards various /-substituted propyl radicals (Scheme 7.3 and Table 7.2). They found that ... 

Table 7.2 Relative Rates for Addition of Substituted Propyl Radicals (R3R2CHCH2CHR1-) to AN and S at 100 °Ca...

Table 7.4 Rate Constants (298 K) for Addition of Substituted Propyl Radicals to (Meth)acrylate Esters (Scheme 7.4)35...

CA, not found 7) J. Smid M. Szwarc, Kinetics of Decomposition of Iso-Butyryl Peroxide and Reactions of Iso-Propyl Radicals , Syracuse Univ, NY, contract DA-30-115-ORD-678 (1958) 8) H.T. Lee et al, Evaluation of... 

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