Reactivity of Alkyl Halides
Effect of Nature of Alkyl Group:
- Alkyl groups are electron donating, therefore more the numbers of alkyl groups attached to the carbon of C-X group leads to greater electron density on this carbon atom, due to which greater repulsion of electron pair towards hydrogen takes place and halogen is released in the form of ion readily.
- The order of reactivity for same halogen group is Tertiary alkyl halide > Secondary alkyl halide > Primary alkyl halide
- In case of primary alkyl halides, the order of reactivity is methyl halide > ethyl halide > propyl halide and so on.
Effect of Nature of Halogen Atom:
- As the size of a halogen atom (atomic number) increases, the ease of substitution of halogen atom increases. Thus the order of reactivity for same alkyl group is R-I > R-Br > R-Cl
- Halogen atoms are highly electronegative. Hence the C-X bond is highly polarised. Hence it becomes a good site for attack by nucleophiles.
- The halogen atom is highly reactive hence can be replaced by another atom or group of atoms.
Order of Reactivity Towards SN1 and SN2 Reactions:
- For SN1 reaction order of reactivity is Tertiary > Secondary > Primary
- For SN2 reaction order of reactivity is Primary > Secondary > Tertiary
Importance of Alkyl Halides:
- Alkyl halides show a variety of chemical reactions which lead to a variety of products.
- Almost all classes of aliphatic organic compounds can be synthesized with the help of alkyl halides.
- Hence alkyl halides (haloalkanes) are regarded as valuable and versatile reagents for preparation of a large variety of organic compounds.
Reactions of Alkyl Halides
- Types of Reactions Exhibited by Alkyl Halides:
Substitution Reactions of Alkyl Halides:
- Reactions with aqueous alkali (Preparation of alcohols)
- Reactions with potassium cyanide (Preparation of alkyl cyanides)
- Reactions with silver cyanide (preparation of alkyl isocyanide)
- Reactions with ammonia (Preparation of primary amine)
- Reaction with sodium alkoxide (preparation of ethers)
- Reactions with a sodium salt of a carboxylic acid (Preparation of esters)
Elimination Reactions of Alkyl Halides:
- Reaction with aqueous alkali (Preparation of alkenes)
Reduction Reactions of Alkyl Halides:
Reactions of Alkyl Halides with Metals:
- Reaction with sodium metal (Preparation of alkanes/ Wurtz reaction)
- Reaction with Magnesium metal (Preparation of Grignard Reagent)