Elimination comparison with substitution

Claisen rearrangement, 1194-1195 dehydration, 622 elimination reactions, 393 oxidation, 625-626 radical reactions, 243-244 characteristics of, 162-164 comparison with laboratory reactions, 162-164 conventions for writing, 162. 190 energy diagram of, 161 reduction, 723-725 reductive animation, 932 substitution reactions, 381-383 Biological reduction, NADH and, 610-611... 

Reactivity toward nucleophiles and comparison with other electrophilic centers 152 Paths for nucleophilic substitution of sulfonyl derivatives 156 Direct substitution at sulfonyl sulfur stereochemistry 157 Direct substitution at sulfonyl sulfur stepwise or concerted 158 The elimination-addition path for substitution of alkanesulfonyl derivatives 166 Homolytic decomposition of a-disulfones 172 10 Concluding remarks 173 Acknowledgement 174 References 174... 

In solvolysis reactions, a silicon at the -position greatly facilitates the heterolysis of a C—X bond, often affording exclusively elimination products (equation 19). Thus, already Sommer, Whitmore and coworkers34,35 described a greatly enhanced reactivity of 60 and 61 in their basic hydrolysis in comparison with the corresponding a- and /-substituted systems. 

Comparison of SN2 and acyl addition-elimination reactions with methoxide as the leaving group. In the concerted SN2, methoxide leaves in a slightly endothermic step, and the bond to methoxide is largely broken in the transition state. In the acyl substitution, methoxide leaves in an exothermic second step with a reactant-like transition state The bond to methoxide has just begun to break in the transition state. 

The third aromatic ring in the anthraquinone derivatives possibly renders all secondary reactions very slow in comparison with the timescale for radical decay. Hydroxyl radicals react wi OH-substituted quinones or other hydroquinones mainly by addition, followed by acid or base catalysed water elimination [55,72]. 

For the purposes of comparison with the nonrelativistic limit, we eliminate the small component from these equations, using (7.27b) to express Q in terms of P and substituting into (7.27a), with the result... 

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