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The halogen atoms in an alkyl halide are electron withdrawing while the alkyl groups have electron donating tendencies. If the electronegative atom (missing an electron, thus having a positive charge) is then joined to a chain of atoms , typically carbon , the positive charge is relayed to the other atoms in the chain.
An electron donating group (EDG) or electron releasing group (ERG, Z in structural formulas) is an atom or functional group that donates some of its electron density into a conjugated π system via resonance (mesomerism) or inductive effects (or induction)—called +M or +I effects, respectively—thus making the π system more nucleophilic.
Although ylides are "electron-rich", they are susceptible to deprotonation of alkyl substituents. Treatment of Me 3 PCH 2 with butyl lithium affords Me 2 P(CH 2) 2 Li. [3] Having carbanion-like properties, lithiated ylides function as ligands. Thus Me 2 P(CH 2) 2 Li is a potential bidentate ligand. [4]
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 alkyl group migrates in the order of thermodynamical stability methyl < primary alkyl < secondary alkyl < tertiary alkyl, this is in line with the radical mechanism. The radical-ketyl pair is short lived and due to a solvent cage effect some isomerizations take place with retention of configuration .
alkyl halide: Chloroethane (Ethyl chloride) ... owing to the electron-withdrawing effect of sp-hybridized oxygen ... and also to form the names of halides and ...
Electron-withdrawing groups exert an "inductive" or "electron-pulling" effect on covalent bonds. The strength of the electron-withdrawing group is inversely proportional to the pKa of the carboxylic acid. [2] The inductive effect is cumulative: trichloroacetic acid is 1000x stronger than chloroacetic acid.
The coupling of an acetylide and tertiary alkyl halide is an example of a reaction that cannot be accomplished with alkali metal acetylides, which displace halides in an S N 2 fashion. The corresponding alkynylalanes are able to couple to tertiary halides via an S N 1-like mechanism. [4] (11)