Alkenes Hofmann elimination

Reacts with tetraalkylammonium salts to yield alkenes (Hofmann elimination Section 24.7). 

There are greater steric problems in approaohing one of the hydrogens in the interior of the molecule thus size of the base operates to favor the less substituted alkene (Hofmann elimination)... 

This reaction is known as the Hofmann elimination, it was developed by August W Hofmann m the middle of the nineteenth century and is both a synthetic method to pre pare alkenes and an analytical tool for structure determination... 

A novel aspect of the Hofmann elimination is its regioselectivity Elimination m alkyltrimethylammonmm hydroxides proceeds m the direction that gives the less substi tuted alkene... 

The least sterically hindered p hydrogen is removed by the base m Hofmann elim matron reactions Methyl groups are deprotonated m preference to methylene groups and methylene groups are deprotonated m preference to methmes The regioselectivity of Hofmann elimination is opposite to that predicted by the Zaitsev rule (Section 5 10) Elimination reactions of alkyltrimethylammonmm hydroxides are said to obey the Hofmann rule, they yield the less substituted alkene... 

With a regioselectivity opposite to that of the Zaitsev rule the Hofmann ehmma tion IS sometimes used in synthesis to prepare alkenes not accessible by dehydrohalo genation of alkyl halides This application decreased in importance once the Wittig reac tion (Section 17 12) became established as a synthetic method Similarly most of the analytical applications of Hofmann elimination have been replaced by spectroscopic methods... 

Hofmann elimination (Section 22 14) Conversion of a quater nary ammonium hydroxide especially an alkyltnmethyl ammonium hydroxide to an alkene on heating Elimination occurs in the direction that gives the less substituted double bond... 

Quaternary ammonium hydroxides undergo elimination on being heated. It is an anti elimination of the E2 type. The regioselectivity of the Hofmann elimination is opposite to that of the Zaitsev rule and leads to the less highly substituted alkene. 

The preparation of an alkene 3 from an amine 1 by application of a /3-elimination reaction is an important method in organic chemistry. A common procedure is the Hofmann elimination where the amine is first converted into a quaternary ammonium salt by exhaustive methylation. Another route for the conversion of amines to alkenes is offered by the Cope elimination. 

Many of the reactions of amines are familiar from past chapters. Thus, amines react with alkyl halides in S 2 reactions and with acid chlorides in nucleophilic acyl substitution reactions. Amines also undergo E2 elimination to yield alkenes if they are first qualernized by treatment with iodomethane and then heated with silver oxide, a process called the Hofmann elimination. 

Name the following amine, including R,S stereochemistry, and draw the product of its reaction with excess iodomethane followed by heating with Ag20 (Hofmann elimination). Is the stereochemistry of the alkene product Z or E Explain. 

Hofmann elimination (Section 24.7) The elimination reaction of an amine to yield an alkene by reaction with iodomethane, followed by heating with Ag2Q. 

ALKENES via HOFMANN ELIMINATION USE OF ION-EXCHANGE RESIN FOR PREPARATION OF QUATERNARY AMMONIUM HYDROXIDES DIPHENYLMETHYL VINYL ETHER... 

When doing this type of sequence, there are a few important things to keep in mind. In the hrst step (elimination), we have a choice regarding which way to eliminate do we form the more substituted alkene (Zaitsev product) or do we form the less substituted alkene (Hofmann product) ... 

The Hofmann elimination is useful synthetically for preparing alkenes since it gives the least substituted alkene. The reaction involves thermal elimination of a tertiary amine from a quaternary ammonium hydroxide these are often formed by alkylation of a primary amine with methyl iodide followed by reaction with silver oxide. The mechanism of the elimination is shown in Scheme 1.13 in this synthesis of 1-methyl-1-... 

The Hofmann elimination converts an amine into an alkene. The process begins by converting an amine to a quaternciry cimmonium salt (that is, it has a nitrogen atom with four bonds). The general mechanism for the elimination step is in Figure 13-40. Figure 13-41 illustrates a sample reaction scheme for the Hofmann elimination. 

Hofmann Elimination Converts an amine into an alkene. 

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