Trichloromethyl radicals, abstraction reactions

This information is, of course, only of a qualitative nature. To obtain a better picture of alkane reactivity in radical abstraction reactions, the activation barrier was computed for the reaction between alkanes and radical reactant. The example used was the reaction between 2-methylpropane, propane, ethane, and methane as alkanes and the trichloromethyl radical as a radical reactant (Table 16). The B3LYP computed activation barriers were not corrected of zero point energy, which is usually 1-2 kcal/mol. With this correction computed, experimental [119] values should be in excellent agreement. As expected, 2-methylpropane was the most susceptible in the hydrogen radical abstraction reaction. With the activation barrier around 8 kcal/mol, it was possible to perform the reaction at a... 

Primary alkyl chlorides are fairly stable to fluorine displacement. When fluorinated, 1-chloropropane is converted to 1-chloroheptafluoropropane and 1-chloto-2-methylbutane produces 39% l-chlorononafluoro-2-methylbutane and 19% perfluoro-2-methylbutane. Secondary and tertiary alkyl chlorides can undergo 1,2-chlorine shifts to afford perfluonnated primary alkyl chlorides 2-Chloro-2-methylpropane gives l-chlorononafluoro-2-methylpropane, and three products are obtained by the fluorination of 3-chloropentane [7] (equation 1). Aerosol fluorina-tion of dichloromethane produces dichlorodifluoromethane which is isolated in 98% purity [4 (equation 2). If the molecule contains only carbon and halogens, the picture is different. Molecular beam analysis has shown that the reaction of fluorine with carbon tetrachlonde, lodotrichloromethane, or bromotrichloromethane proceeds first by abstraction of halogen to form a trichloromethyl radical [5]... 

We see that the effect of multidipole interaction plays an important role in all reactions of abstraction and addition of polar reactants. This interaction can increase or decrease the activation energy of the reaction. However, the multidipole interaction does not influence the reactions of nonpolar trichloromethyl radicals with mono- and polyatomic esters due to the nonpolar character of the attacking radical [89]. 

The radical reaction of carbon tetrachloride with aliphatic double bonds involves addition of the trichloromethyl radical to the double bond, followed by chlorine atom abstraction from carbon tetrachloride by the intermediate radical to give the product. After the addition of the trichloromethyl radical to /3-pinene, a fragmentation occurs prior to formation of the product. 

Addition of metal catalysts, most commonly CuCl and FeCb, can allow for clean formation of 1 1 adducts. A large number of other metals and salts have been shown to catalyze reactions of this type. A mechanism for processes of this type [42], whose certain aspects have been called into question [43], is as shown in Scheme 14. In this variation on the typical atom transfer process, it is proposed that the CuCl abstracts a Cl atom to form the trichloromethyl radical, which adds to the olefin. The subsequently formed radical, instead of abstracting Cl from CCI4, a slow process, reacts with CuCli to complete the atom transfer addition. 

Miscellaneous Reactions. 1.2.1 Addition Reactions - A novel photochemical reaction of stilbene in carbon tetrachloride solution has been described. Irradiation of this system populates the first excited singlet state of stilbene which then abstracts a halogen from the solvent. The resulting radical pair composed of a trichloromethyl radical and (14) yields the products. 

The trichloromethyl radical might combine directly with biological molecules, causing covalent modification, as well as abstracting hydrogen from membrane lipids, setting off the chain reaction of lipid peroxidation. The most rapid reaction is with molecular oxygen to form the trichloromethylperoxy radical ... 

Thermolysis of 59 in chloroform (17) led to formation of carbonyl ylide 64, subsequent proton abstraction from chloroform (p fa = 24.1), and recombination with the trichloromethyl anion gave acetal 65. The intermediacy of radicals was discounted since conducting the reaction in neat BuaSnH did not change the product distribution. 

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