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Eliminations Saytzeff

A study of Hofmann vs Saytzeff elimination from 2-bromooctane under soliddiquid two-phase conditions [6] shows that the 1-octene 2-octene ratio depends not only on the base used, but also on the catalyst. Aliquat is the most effective catalyst giving a 98% overall yield with a l-octene 2-octene ratio of ca. 2 1. Benzyltriethylammonium chloride catalyses a 95% conversion with a ratio of ca. 3 1 in favour of the 1-octene. Potassium hydroxide and potassium t-butoxide favour the formation of 1-octene, whereas sodium methoxide and sodium ethoxide favour the formation of 2-octene [6]. [Pg.391]

Thionyl chloride behaves in some circumstances as though it dehydrates by fram -diaxial elimination, as described for phosphorous oxychloride. For example, the 5a-alcohol (102) undergoes anti-Saytzeff elimination to give the A4-olefin. In this particular example, phosphorous oxychloride-pyridine does not work, and acetic anhydride-sulfuric acid gives the A5-isomer (ref. 185, p. 199). [Pg.433]

Hofmann elimination loss of a proton leading preferentially to the alkene carrying the smaller number of alkyl groups (cf Saytzeff elimination below)... [Pg.1067]

Alkenes may be obtained by elimination reactions from alkyl haUdes, alcohols, sulfonates or amines. The substitution pattern of the alkene and the stereospecificity of these methods depend quite subtly on the structure of the individual substrate. If the leaving group occupies an unsymmetrical position in a compound, one of two isomeric alkenes can be formed (Scheme 3.1). Elimination to give an alkene bearing the greatest number of alkyl groups is known as the Saytzeff elimination and is commonly found with alkyl halides. When the elimination gives preferentially the less-substituted alkene, it is known as the Hofmann elimination This substitution pattern is commonly foimd with the elimination of alkylammonium salts. In practice, mixtures of alkenes are often obtained. [Pg.64]

Hofmann degradation of 5of-cholestan-4a- and -4/3-yI trimethylammonium salts closely resembled that of the C-6 quaternary ammonium salts the 4j -compound producing solely the 4-ene by Saytzeff elimination whilst the 4a-epimer gives largely demethylated 4a-dimethylamino-steroid, with some 3-ene. ... [Pg.488]

The tendency for the Saytzeff elimination to give trons-2-hexene followed the trend F < Cl < Br < I. Some substitution product, 2-hexyl methyl ether, was also formed in the reactions. [Pg.663]

Finally, as foreshadowed in Chapter 7 (Scheme 7.24 ft, the Hofmann elimination) and Chapter 8, Part I, Section F, A. W. Hofmann (1818-1895) pointed out that elimination from ammonium ions yielded the least highly substituted alkene rather than the most highly substituted alkenes (the Saytzeff elimination). Thus, as shown in Scheme 10.47, when 2-aminobutane is exhaustively methylated with iodomethane (ICH3) and treated with base, there is more ehmination to yield 1-butene (about 60%) than when, for example, the same elimination reaction is effected on 2-bromobutane (about 20%). It has been argued that this result comes about because the base is closely associated with the positively charged ion and the hindered environment favors loss of the proton from the primary carbon. [Pg.994]

With El reactions, Saytzeff elimination dominates because the transition state for proton removal from the carbenium ion has double bond character. Since substitution by electron... [Pg.588]

Relative Percentages of Hofmann and Saytzeff Elimination Using Various Experimental Conditions ... [Pg.590]

FIGURE 7.72 The more substituted (more stable) alkene is favored in the El reaction, even when statistical factors favor the less substituted isomer. This reaction is known as Saytzeff elimination. [Pg.299]

In the example shown in Rgure 7.92, the transition state for Hofmann elimination has a partial negative charge on a primary carbon, whereas the transition state for Saytzeff elimination has a partial negative charge on a secondary carbon (Rg. 7.92). [Pg.310]

FIGURE 7.92 In the ElcB-like transition state for Hofmann elimination, a partial primary carbanion (less substituted, more stable) is formed. In the ElcB-like transition state for Saytzeff elimination, it is a partial secondary carbanion (more substimted, less stable). [Pg.310]

Second, there is a unimolecular El elimination reaction that parallels (and competes with) the SnI substitution reaction. The SnI and El reactions share the same intermediate, the carbocation formed by ionization of the leaving group. Once this carbocation is formed it can be captured by nucleophiles (SnI) or deprotonated to give an alkene (El). Saytzeff elimination is the rule. [Pg.311]

E1 reaction. Must be a tertiary or secondary halide. Saytzeff elimination. Competes with the 3 1 reaction... [Pg.322]

Saytzeff elimination reaction, 19 Schiff base, 94, 234 formation, 235... [Pg.326]


See other pages where Eliminations Saytzeff is mentioned: [Pg.249]    [Pg.249]    [Pg.339]    [Pg.342]    [Pg.172]    [Pg.190]    [Pg.199]    [Pg.358]    [Pg.408]    [Pg.64]    [Pg.31]    [Pg.50]    [Pg.134]    [Pg.465]    [Pg.264]    [Pg.658]    [Pg.659]    [Pg.588]    [Pg.306]    [Pg.308]    [Pg.311]   
See also in sourсe #XX -- [ Pg.391 ]

See also in sourсe #XX -- [ Pg.209 ]

See also in sourсe #XX -- [ Pg.357 ]

See also in sourсe #XX -- [ Pg.64 ]

See also in sourсe #XX -- [ Pg.106 ]

See also in sourсe #XX -- [ Pg.525 , Pg.526 , Pg.527 , Pg.536 , Pg.547 , Pg.665 , Pg.666 , Pg.675 , Pg.714 , Pg.862 , Pg.994 ]

See also in sourсe #XX -- [ Pg.588 ]

See also in sourсe #XX -- [ Pg.300 , Pg.306 , Pg.308 , Pg.310 , Pg.322 ]




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Formation of Regioisomeric Alkenes by 3-Elimination Saytzeff and Hofmann Product(s)

Saytzeff

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