Leaving group, in nucleophilic

Methyl bromide slowly hydrolyzes in water, forming methanol and hydrobromic acid. The bromine atom of methyl bromide is an excellent leaving group in nucleophilic substitution reactions and is displaced by a variety of nucleophiles. Thus methyl bromide is useful in a variety of methylation reactions, such as the syntheses of ethers, sulfides, esters, and amines. Tertiary amines are methylated by methyl bromide to form quaternary ammonium bromides, some of which are active as microbicides. 

SuIfona.tlon, The sulfonic acid group is used extensively in the dyes industry for its water-solubilizing properties, and for its ability to act as a good leaving group in nucleophilic substitutions. It is used almost exclusively for these purposes since it has only a minor effect on the color of a dye. 

Isopentenyl pyrophosphate and dimethylallyl pyrophosphate are structurally similar—both contain a double bond and a pyrophosphate ester unit—but the chemical reactivity expressed by each is different. The principal site of reaction in dimethylallyl pyrophosphate is the carbon that bears the pyrophosphate group. Pyrophosphate is a reasonably good leaving group in nucleophilic substitution reactions, especially when, as in dimethylallyl pyrophosphate, it is located at an allylic carbon. Isopentenyl pyrophosphate, on the other hand, does not have its leaving group attached to an allylic carbon and is far- less reactive than dimethylallyl pyrophosphate toward nucleophilic reagents. The principal site of reaction in isopentenyl pyrophosphate is the carbon-carbon double bond, which, like the double bonds of simple alkenes, is reactive toward electrophiles. 

The -R and -H in these compounds can Tact as leaving groups in nucleophilic substitution reactions. 

The -OH, -X, -OR, -SR, -NH2, -0C0R, and -0P032- in these compounds can act as leaving groups in nucleophilic substitution reactions. 

It s this ability to drive otherwise unfavorable phosphorylation reactions that makes ATP so useful. The resultant phosphates are much more reactive as leaving groups in nucleophilic substitutions and eliminations than the corresponding alcohols they re derived from and are therefore more likely to be chemically useful. 

Tosylate (Section 11.1) A p-toluenesulfonate ester useful as a leaving group in nucleophilic substitution reactions. 

Although halides are common leaving groups in nucleophilic substitution for synthetic purposes, it is often more convenient to use alcohols. Since OH does not leave from ordinary alcohols, it must be converted to a group that does leave. One way is protonation, mentioned above. Another is conversion to a reactive ester, most commonly a sulfonic ester. The sulfonic ester groups tosylate, brosylate, nosylate, and mesylate are better leaving groups than... 

The fact that the 3,5-dimethylpyrazol-l-yl moieties of 1,2,4,5-tetrazine 63 are good leaving groups in nucleophilic displacements has been used for the synthesis of azotetrazine 66, a novel high-nitrogen energetic material <00AG(E)1791>. 

Groups that generally function well as leaving groups in nucleophilic aromatic photosubstitution are the methoxy(alkoxy)-group and the nitro-group. 

Problem 16.33 Use the Hammond principle (Problem 11.8) to explain why strong bases such as OR (from esters) and NH, (from amides) can be leaving groups in nucleophilic transacylations. ... 

Since H20 is known to be a good leaving group in nucleophilic substitutions at square planar platinum(II)49, the final step in reaction (37) would be expected to be very rapid with MeOH as the leaving group. 

Recall that p-toluenesul Innate (tosylate) is a good leaving group in nucleophilic substitution reactions. The nucleophile that displaces tosylate from carbon is the alkoxide ion derived from the hydroxyl group within the molecule. The product is a cyclic ether, and the nature of the union of the two rings is that they are spirocyclic. 

The combination of addition and elimination reactions has the overall effect of substituting one nucleophile for another in this case, substituting an alcohol for water. The rate of these nucleophilic substitution reactions is determined by the ease with which the elimination step occurs. As a rule, the best leaving groups in nucleophilic substitutions reactions are weak bases. The most reactive of the carboxylic acid derivatives are the acyl chlorides because the leaving group is a chloride ion, which is a very weak base (ATb KT20). 

The preparation of tosylate and other sulfonate esters for use as leaving groups in nucleophilic substitution reactions (see Section 8.9) employs the reaction of a sulfonyl chloride (an acid chloride of a sulfonic acid) with an alcohol. Another example is shown in the following equation. Note the similarity of this reaction to the reaction of an acyl chloride with an alcohol to form an ester. 

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