electrophile - Electrophiles in organic chemistry

An entity with a deficiency of electrons which tends to react at a negatively charged centre. Most electrophiles are cations.

In chemistry, an electrophile (literally electron-lover) is a reagent attracted to electrons that participates in a chemical reaction by accepting an electron pair in order to bond to a nucleophile.

The electrophiles attack the most electron-populated part of a nuculeophile. The electrophiles frequently seen in the organic syntheses are cations such as H, polarlized neutral molecules such as HCl, alkyl halides, acyl halides, and carbonyl compounds, polarlizable neutral molecules such as Cl2 and Br2, oxidizing agents such as organic peracids, chemical species that do not satisfy the octet rule such as carbenes and radicals, and some of lewis acids such as BH3 and DIBAL.

Electrophiles in organic chemistry

Alkenes

Electrophilic addition is one of the three main forms of reaction concerning alkenes.

Addition of halogens

These occur between alkenes and electrophiles, often halogens. For example, ethylene + bromine → 1,2-dibromoethane:

C2H4 + Br2 → BrCH2CH2Br

This takes the form of 3 main steps shown below; The three-membered bromonium ion 2 consisted with two carbon atoms and a bromine atom forms with a release of Br−. The direct convertion of 1 to 3 will appear when the Br

Addition of hydrogen halides

Hydrogen harides such as hydrogen chloride (HCl) adds to alkenes to give alkyl halide. An example shown below:

Proton (H+) adds (by working as an electrophile) to one of the carbon atoms on the alkene to form cation 1.

This process is called A-SE2 mechanism. Hydrogen fluoride (HF) and hydrogen iodide (HI) react with alkenes similary and Markovnikov-type products will be given.

Hydration

One of the more complex reactions utilises sulfuric acid as a catalyst. This reaction occurs in a similar way to the addition reaction but has an extra step in which the OSO3H group is replaced by an OH group, forming an alcohol:

C2H4 + H2O → C2H5OH

As you can see the H2SO4 does not take part in the overall reaction, however it does take part but remains unchanged so is clasified as a catalyst.

This is the reaction in more detail:

The H-OSO3H molecule has a δ+ charge on the initial H atom, this is attracted to and reacts with the double bond in the same way as before. When water (H2O) is added and the mixture headed ethanol is produced (C2H5OH) is produced, the "spare" hydrogen atom from the water goes into "replacing" the "lost" hydrogen and thus reproduces sulfuric acid.

Overall this process adds a molecule of water to a molecule of ethene.

This is an important reaction in industry as it produces ethanol, which is the alcohol having various purposes including fuels and starting material for other chemicals.