Saytzev elimination

The preference for Saytzev elimination in the El pathway has already been referred to (p. 249). 

The proportion of Hofmann elimination is also found to increase with increasing branching in the alkyl group of the substrate (constant Y and base), and with increasing branching in the base, e.g. with (43), a bromide where preferential Saytzev elimination would normally be expected ... 

These several steric effects are explainable on the basis that any crowding, irrespective of its origin, will make the T.S. (44) that involves the removal of proton from (46a)—Saytzev elimination—relatively more crowded than the T.S. (45) that involves removal of proton (D from (46b)—Hofmann elimination. The differential will increase as the crowding increases (in R, Y or B), and Hofmann elimination will thus be progressively favoured over Saytzev ... 

Sandmeyer reaction, 306 Sandwich compoimds, 275 Sawhorse projections, 7 Saytzev elimination, 249, 256 Schiff bases, 221 Schmidt rearrangement, 122 Selectivity, 156, 169, 326 a, 362 a, 370 372 aj,385 a bonds, 6 o complexes, 41,131 Sigmatropic rearrangements, 352-357 antarafacial, 353 carbon shifts, 354 hydrogen shifts, 352 orbital symmetry in, 352 photochemical, 354 suprafadal, 353 thermal, 353... 

Which product results from Saytzev elimination, and which from Hofmann elimination ... 

Two minor products E and Z isomers, shown below) arise from Saytzev elimination. 

This is a review of the material from Sections 7-6 and 7-7. There arc two new considerations. First, many haloalkanes can give rise to several alkenes upon elitninalion, each with the double bond in a different position in the carbon chain. These products ari.se when there arc several different P-hydrogens that can be lost in the elimination process together with the leaving group. The nile to remember is as follows All El and, with one main exception, all E2 proces.ses tend 10 produce the most highly substituted, most stable alkcne (Saytzev elimination). The major exception is that very bulky ba.ses will favor production of the least substituicd, least stable nlkenc in E2 processes (Hofmann elimination). 

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