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An application of HSAB theory is the so-called Kornblum's rule (after Nathan Kornblum) which states that in reactions with ambident nucleophiles (nucleophiles that can attack from two or more places), the more electronegative atom reacts when the reaction mechanism is S N 1 and the less electronegative one in a S N 2 reaction.
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 are Lewis bases. Nucleophilic describes the affinity of a nucleophile to bond with positively charged ...
Here, a strong Lewis acid is required to generate either a carbocation from an alkyl halide in the Friedel-Crafts alkylation reaction or an acylium ion from an acyl halide. In the vast majority of cases, reactions that involve leaving group activation generate a cation in a separate step, before either nucleophilic attack or elimination.
The methoxide anion, for example, is both a strong base and nucleophile because it is a methyl nucleophile, and is thus very much unhindered. tert -Butoxide , on the other hand, is a strong base, but a poor nucleophile, because of its three methyl groups hindering its approach to the carbon.
Butyllithium is a strong base (pK b ≈ -36), but it is also a powerful nucleophile and reductant, depending on the other reactants. Furthermore, in addition to being a strong nucleophile, n -BuLi binds to aprotic Lewis bases, such as ethers and tertiary amines , which partially disaggregate the clusters by binding to the lithium centers.
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 − ).
In chemistry, an alkoxide is the conjugate base of an alcohol and therefore consists of an organic group bonded to a negatively charged oxygen atom. They are written as RO −, where R is the organyl substituent. Alkoxides are strong bases [citation needed] and, when R is not bulky, good nucleophiles and good ligands.
Simple mechanism for base-catalyzed aldol reaction of an aldehyde with itself. Base-catalyzed dehydration. Simple mechanism for the dehydration of an aldol product. Although only a catalytic amount of base is required in some cases, the more usual procedure is to use a stoichiometric amount of a strong base such as LDA or NaHMDS. In this case ...