Chemical Reactivity of Haloalkanes| UPTGT PGT Chemistry

This video is for UPTGT / PGT Chemistry.
In this video I explained haloalkanes and Haloarenes.
This video is Part - 5 of the chapter.
And in this part I have discussed the Chemical Properties of Haloalkanes.
Chemical Properties of Haloalkanes
Nature of C-X Bond:
• C-X bond is highly polarised due to large difference in their electronegativity.
• The halogen atom is far more electronegative than carbon and tends to pull the electron away from carbon,
i.e. halogen acquires a small negative charge and carbon a small positive charge.
• Reactivity of haloalkanes depends upon cleavage of C-X bond.
There are 4 types of Chemical reaction of Haloalkanes:
1.Nucleophilic Substitution Reaction
2.Elimination Reaction
3.Reaction with Metals
4.Reduction
1. Nucleophilic Substitution Reaction:
• Nucleophiles are electron rich species. They attack at the part of substrate molecule which is electron deficient.
• When an atom or group of atom is replaced by a nucleophile, the reaction is called Nucleophilic substitution reaction.
• There are two types of Nucleophilic substitution reaction for haloalkanes:
1. Nucleophilic Substitution Unimolecular (SN1)
2. Nucleophilic Substitution Bimolecular (SN2)
1. Unimolecular Nucleophilic Substitution (SN1):
• Those substitution reactions in which rate of reaction depend upon the conc. of one reactant only.
• SN1 reactions are generally carried out in polar protic solvent such as Water , alcohol and acetic acid.
• Hydrolysis of Tert-Butyl chloride follows SN1 reaction.
• This reaction take place in two steps:
Step 1: The polarised C—X bond undergoes slow cleavage to produce a carbocation and a bromide ions. (Slow step and rate determining step).
Step 2: The carbocation is then attacked by Nucleophile to complete the substitution reaction.
2. Bimolecular Nucleophilic Substitution (SN2):
• Those substitution reactions in which rate of reaction depends on the conc. Of two species, alkyl halide and nucleophile.
• They involve one step mechanism. Back side attack of nucleophile and departing of leaving group take place simultaneously.
• Non-polar solvents favour SN2 mechanism.
Reaction related to Nucleophilic Substitution:
1. Replacement of hydroxyl group (---OH) (Formation of Alcohols)
• Haloalkanes are hydrolysed to alcohols by moist Silver oxide (AgOH) or by Boiling with aq. Alkali soln (NaOH or KOH).
2. Replacement of alkoxy group (---OR) (Formation of ether):
• By heating sodium/ potassium alkoxides or with silver oxide (Ag2O) form ethers.
• Nucleophile is ---OR
3. Replacement of hydrosulphide group (---SH) (Formation of thioalcoholsor mercaptans):
• By heating aq. Or alc. sodium/ potassium hydrogen sulphide,
• Nucleophile is ---SH
4. Replacement of cyano group (---CN) (Formation of alkyl cyanides or nitrile):
• In the presence of alc. KCN
• Nucleophile is ---CN
5. Replacement of isocyanide group (--N≡C) (Formation of isocyanides):
• In the presence of alc. AgCN
• Nucleophile is ---N≡C
6. Replacement of nitrite group (--O—N=O) (Formation of alkyl nitrite):
• In the presence of alc. K--O—N=O
• Nucleophile is --O—N=O
7. Replacement of nitro group (--NO2) (Formation of nitroalkanes):
• In the presence of alc. AgNO2
• Nucleophile is --NO2
8. Replacement of amino group (--NH2) (Formation of amines):
• On heating with NH3
• Nucleophile is --NH2
9. Replacement of carboxylic (--COOR) (Formation of ester):
• On heating with silver salts of fatty acids
• Nucleophile is –COOR’
10. Replacement of Alkynl group (--C≡C--) (Formation of higher alkyne):
• On heating with Na---C≡CH
• Nucleophile is --C≡CH
2. Elimination Reaction:
Dedhydrohalogention
• In the presence of conc. Alcoholic soln of potassium hydroxide (KOH), haloalkane form alkene by dehydrohalogenation.
• These reaction are called β-elimination reaction bcoz Hatom of haloalkane which is eliminated comes form βcarbon. (carbon next to carbon from which halogen is attached).
Saytzeff’s Rule:
• In the dehydrohalogenation of 2° and 3° haloalkanes, the hydrogen atom is eliminated from the adjacent carbon atom with lesser of H-atom i.e. the more substituted alkane is more stable.

3. Reaction with metals:
• Most organic halides react with certain metals to give compounds containing carbon-metal bonds.
• Such compounds are known as Organo-metallic Compounds.
a. Reaction with Magnesium (formation of Grignard Reagent):
C2H5Br + Mg
• Grignard Reagent is highly reactive and form corresponding hydrocarbon on reacting with water, alcohols and amines.
R—Mg-X + H2O → R—X + Mg(OH)X
b. Reaction with Sodium (Wurtz Reaction):
• Haloalkanes reacts with sodium metal in dry ether to give hydrocarbon containing double the no. of carbon present in halide.
2R--X + 2Na → R—R + 2NaX
4. Reduction:
• Haloalkanes get reduced in the presence of Zn and dil. HCl. To form alkanes.
R--X + 2H →


Join Our Telegram Group:
https://t.me/stepupclasses02

Regards,
Step Up Classes