Alkyl replacement

P/Z) values below 200 atm other observed hot reactions involve direct replacements of singly bound atoms or alkyl radicals by atomic F. These F-for-X atomic substitution and F-for-fl alkyl replacement processes typically form excited organic products. Small yields of H F, which follow from secondary decomposition reactions of such species, can be estimated from the respective reaction mechanisms. 

F-for-aH, and F-for- H atomic substitution together with F-for-CHs and -g F-for-CHFa alkyl replacement. Equations 18-22, respectively. The dagger... 

From Table XII all the energetic substitution channels in CH8CHF2 exhibit apparait )deld enhancements in the 303 K and 195 K liquid phases. However, caging reactions do not contribute to the alkyl replacement yields in either condensed CH3CHF2 or CHsCFs at temperatures as low as 195 K (26,28,31,35). 

The average fractional decomposition at low (P/Z) for the nascent alkyl replacement products in CH8CHF2 exhibits the value 0.24 0.03. The corresponding result for the substitution products is 0.79 0.02. Similarly, the alkyl replacement species undergo complete collisional stabilization below 10 atm, whereas the average fractional stabilization of the activated substitution products at 190 atm is only 0.45 0.10. The excitation levels accompanying primary substitution Reactions 18-20 apparently are much larger than those for alkyl replacement Reactions 21 and 22. 

For CH3CF3 only 0.27 0.04 average fractions of the nascent alkyl replacement products are capable of decomposing, and these unimolecular processes are subject to complete collisional stabilization above approximately 12 atm. The corresponding average fractional decomposition and stabilization (P/Z) values for CH3CHF2 are 0.24 it 0.03 and approximately 10 atm. 

This striking contrast in decomposition behavior between the products from recoil F substitution and alkyl replacement reactions is intriguing, but its dynamical basis remains uncertain. Cold"" alkyl replacement products could conceivably result from either of the follovsdng extreme mechanisms (i) 3-center direct reactions in which product internal excitation is confined to the newly formed bond or (ii) dynamically more complex processes that are Golden Rule forbidden (57,79,80) at large collision energies. The further study of this question r resents a fertile area for future research. 

Figure 8. Approximate thermochemical excitation energy distributions for the F-for-k alkyl replacement channels in CHfiHF (28, 77)...

Benzene undergoes many substitution reactions in which some group such as halogen, sulfonic acid (SO3H), nitro (NO2), or alkyl replaces hydrogen ... 

Wang Zhonggang, Chen Tianlu, Xu Jiping. (1995). Synthesis and Characteristics of Card Polyarylesterketones with Various Alkyl Replacers. Acta Polym. Sin, 4, 494 98. 

The species at the centre of tire rings is usually Si or Ge and tire bridging atom is oxygen. In one study tire peripheral hydrogens on tire phtlialocyanine molecules were replaced by alkyl groups and tire resulting polymers could be rendered soluble in ordinary organic solvents [108, 109 and 110]. Successful deposition of several of tliese materials has been achieved and different techniques were employed to study tlieir stmctural properties [109, ill, ill, ill and 1141. 

In silicon tetrachloride, SiC, chlorine atoms can be replaced by methyl or other alkyl groups to give, for example, CHjSiClj and (CH3)2SiCl2. These two compounds are obtained when methyl... 

The preparation of acetophenone (p. 255) is a modification of this method, the alkyl halide being replaced by an acid chloride, with the consequent formation of a ketone. 

If only the monocarboxybc acid is required, the ester after hydrolysis with potash may be strongly acidified with sulphuric acid and the mixture heated under reflux the mineral acid promotes decarboxylation at a temperature just above 100°. The net result is the replacement of the halogen atom of the alkyl halide by —CH COOH thus in the above example ... 

Some observations about the nitration of some polymethylbenzenes have already been made ( 6.3, 6.4). Replacement of an alkyl group has frequently been observed, but quantitative studies are laeking. 

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