Vinyl Halide Substitution

From the perspective of applications the dominant member of this class of compounds is vinyl chloride which is produced on the scale of millions of.

Vinyl halide substitution. Vinylic halides resemble alkenes in that they undergo addition to their double bond. This lack of reactivity is due to several factors. Vinylic and aryl halides however are virtually inert to the conditions that promote s n1 or e1 reactions of alkyl halides. So the bond between the chlorine and the carbon in the double bond is much too strong stronger than that of an alkyl chloride to be broken by a nucleophile sn2.

An example is the addition of hydrogen chloride to vinyl chloride to yield 1 1. Mide undergoes a rapid solvolysis in ethanol to give both substitution and elimination products. Likewise phenyl cations are unstable thus making s n 1 reactions impossible. An aryl halide or a vinyl halide are electron withdrawing groups i e nucleophiles and nucleophiles cannot be attacked by a nucleophile and are more prone to electrophilic reactions than nucleophilic reactions.

For this reason alkenyl halides with the formula rch chx are sometimes called vinyl halides. Rapid s n 2 substitution for 1º and 2º halides. For 3º halides a very slow s n 2 substitution or if the nucleophile is moderately basic e2 elimination. Vinylic halides may be converted to grignard reagents by reaction with magnesium and these reagents undergo the same types of reaction as those derived from alkyl halides.

Certain vinylic halides can be forced to react by the s n1 e1 mech. Simple aryl halides like chlorobenzene are very resistant to nucleophilic substitution. It is possible to replace the chlorine by oh but only under very severe industrial conditions for example at 200 c and 200 atmospheres. Nucleophilic substitution occurs readily only when electron withdrawing groups are present at suitable positions.

In organic chemistry a vinyl halide is a compound with the formula ch 2 chx x halide the term vinyl is often used to describe any alkenyl group. Rapid s n 2 substitution for 1º halides note there are no β. In addition the. Aryl halides are less reactive towards nucleophilic substitution reaction as compared to alkyl halides due to resonance stabilization.

Aryl halides are relatively unreactive toward nucleophilic substitution reactions. Nucleophilic substitution via the s n 1 or s n 2 mechanism does not generally occur with vinyl or aryl halides or related compounds. Under certain conditions nucleophilic substitutions may occur via other mechanisms such as those described in the nucleophilic aromatic substitution article. In high dielectric ionizing solvents such as water dimethyl sulfoxide acetonitrile s n 1 and e1 products may be observed.

Due to resonance c c l bond acquires partial double bond character and becomes shorter and stronger and cannot be easily replaced by nucleophiles.