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A hydroxide ion acting as a nucleophile in an S N 2 reaction, converting a haloalkane into an alcohol. In chemistry, a nucleophile is a chemical species that forms bonds by donating an electron pair. All molecules and ions with a free pair of electrons or at least one pi bond can act as nucleophiles. Because nucleophiles donate electrons, they ...
The nucleophile may be electrically neutral or negatively charged, whereas the substrate is typically neutral or positively charged. An example of nucleophilic substitution is the hydrolysis of an alkyl bromide, R-Br under basic conditions, where the attacking nucleophile is hydroxyl (OH −) and the leaving group is bromide (Br −).
This is because α-nucleophiles showing the α-effect have smaller HOMO(nucleophile)-LUMO(substrate) gap, in other words, high HOMO energy level that allows more orbital interaction. Examples of α-nucleophiles with α-effects are shown in Figure 4. The α-nucleophiles have smaller HOMO lobes than the parent normal nucleophile. Figure 4.
The examples in textbooks of secondary substrates going by the S N 1 mechanism invariably involve the use of bromide (or other good nucleophile) as the leaving group have confused the understanding of alkyl nucleophilic substitution reactions at secondary carbons for 80 years [3].
A nucleophilic aromatic substitution (S N Ar) is a substitution reaction in organic chemistry in which the nucleophile displaces a good leaving group, such as a halide, on an aromatic ring. Aromatic rings are usually nucleophilic, but some aromatic compounds do undergo nucleophilic substitution.
Carboxylate ions are good nucleophiles. They react with alkyl halides to form esters. The following reaction shows the reaction mechanism. [1]: 398–9 The S N 2 reaction between sodium acetate and bromoethane. The products are ethyl acetate and sodium bromide.
The physical manifestation of leaving group ability is the rate at which a reaction takes place. Good leaving groups give fast reactions. By transition state theory, this implies that reactions involving good leaving groups have low activation barriers leading to relatively stable transition states.
The nucleophile is polarised and oriented by the base, which is itself bound and stabilised by the acid. [24] Catalysis is performed in two stages. First, the activated nucleophile attacks the carbonyl carbon and forces the carbonyl oxygen to accept an electron pair, leading to a tetrahedral intermediate. The resulting build-up of negative ...