In elimination reactions

The stereochemistry of reactions can also be treated by permutation group theory for reactions that involve the transformation of an sp carbon atom center into an sp carbon atom center, as in additions to C=C bonds, in elimination reactions, or in eIcctrocycHc reactions such as the one shown in Figure 3-21. Details have been published 3l]. 

Stereoselectivity was defined and introduced in connec tion with the formation of stereoisomeric alkenes in elimination reactions (Sec tion 5 11)... 

The use of DMSO as a sol vent in elimination reactions was mentioned earlier in Section 5 14... 

The nature of the transition state in elimination reactions is of great importance, since it controls the regiochemistry of p elimination in compounds in which the double bond can be introduced in one of several positions. These effects are discussed in the next section. 

Practically everything we ve said in previous chapters has been stated without any proof. We said in Section 6.8, for instance, that Markovnikov s rule is followed in alkene electrophilic addition reactions and that treatment of 1-butene with HC1 yields 2-chJorobutane rather than 1-chlorobutane. Similarly, we said in Section 11.7 that Zaitsev s rule is followed in elimination reactions and that treatment of 2-chlorobutane with NaOH yields 2-butene rather than 1-butene. But how do we know that these statements are correct The answer to these and many thousands of similar questions is that the structures of the reaction products have been determined experimentally. 

S-N bond cleavage 159 S-O bond lengths 543 Solvated electrons 897, 905 Solvent effects 672 in elimination reactions 772 S-O stretching frequencies 543, 545, 546, 552-555, 560-562 Spiroconjugation 390 Stereoselectivity 779, 789 of cylcoaddition reactions 799 of sulphones 761 Steroids... 

If carbocations are intermediates, we should expect rearrangements with suitable substrates. These have often been found in elimination reactions performed under El conditions. 

Effect on Reactivity. The leaving groups in elimination reactions are similar to those in nucleophilic substitution. The E2 eliminations have been performed with the following groups NRj, PR, SRj, OHR", SO2R, OSO2R,... 

These studies on steric assistance (12) led to a detailed consideration of the possible role of steric effects in a wide variety of systems, such as steric effects in displacement reactions 10, 14), steric effects in elimination reactions 15,16), steric effects in alicyclic systems (77), and steric effects in... 

We have already seen examples of carbanions involved as intermediates, e.g. (40), in elimination reactions, i.e. those that proceed by the ElcB pathway (p. 251), for example ... 

Cyclic Nitronates The chemistry of cyclic nitronates substantially differs from the chemistry of their acyclic analogs. Cyclic nitronates are involved predominantly in various rearrangements rather than in elimination reactions. The character and pathways of these rearrangements are determined not only by the nature of the reagent used but also by the character of the heterocycle and the nature of the substituents attached to the heterocycle. 

Additional Transformation Reactions. Other reactions that can be catalyzed by mineral surfaces are substitution, elimination, and addition reactions of organic molecules. Substitution and elimination are two general types of reactions that occur at saturated carbon atoms of organic molecules. Both types are initiated by nucleophilic attack however, in elimination reactions it is the basicity of the nucleophile that determine its reactivity rather than its nucleophilicity. Since mineral surfaces are expected to have both nucleophilic and basic properties, these types of reactions should also occur at mineral-water interfaces (see Chapter 22). It remains to be shown whether or not these reactions are catalyzed under environmental conditions. 

Structural effects on the secondary KIEs in elimination reactions 229... 

STRUCTURAL EFFECTS ON SECONDARY KIEs IN ELIMINATION REACTIONS... 

Saunders, W.H. (1985). Calculations of isotope effects in elimination reactions. New experimental criteria for tunneling in slow proton transfers. J. Am. Chem. Soc. 107, 164-169... 

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