Important Chemical Reactions for Class 12 Chemistry
Here are some important chemical reactions which every student of class 12 must have a thorough understanding of. All Organic Naming reactions for 12th Board Exam. Last Minute Chapter wise revision by Advanced Chemistry.
Chapter 10 Haloalkanes and Haloarenes
The Finkelstein reaction is an organic reaction where an alkyl halide is converted into another alkyl halide by reacting with a metal halide salt. This is an equilibrium process and it is driven forward by taking advantage of the poor solubility in acetone of the newly formed metal halide salt (Le Chatelier’s principle).
When alkyl chloride is heated in the presence of a metallic fluoride like AgF, Hg2F2, SbF3 or CoF2, we get alkyl fluorides.
When Alkyl halides get reacted with sodium with dry ether, we get hydrocarbons that include the double number of carbon atoms present in the halide. This is known as the Wurtz Reaction
Fittig Reaction: When two moles of aryl halide reacts with two moles of sodium(Na) in presence of dry ether then biphenyl is obtained. This reaction is known as Fitting reaction
Friedel-Crafts alkylation Reaction:
Benzene is prepared with an alkyl halide in the presence of anhydrous aluminum chloride to give Alkylbenzene.
Friedel-Crafts acylation reaction:
We get acyl benzene when an acyl halide is reacted with benzene in the presence of Lewis acids.
Chapter 11 Alcohols, Phenols and Ethers
Hydroboration-Oxidation is a two step pathway used to produce alcohols. The reaction proceeds in an Anti-Markovnikov manner, where the hydrogen (from BH3
) attaches to the more substituted carbon and the boron attaches to the least substituted carbon in the alkene bouble bond.
For example: – When propene undergoes hydroboration-oxidation reaction, then it produces propan-1-ol as product. In this reaction diborane i.e., (BH3)2 reacts with propene, which in result generates trialkyl borane as an addition product. Then trialkyl borane is oxidised, by using hydrogen peroxide in the presence of aqueous sodium hydroxide to form alcohol, as final product.
Oxymercuration Demercuration reaction:
A reaction in which an alkene is reacted with a Hg2+
salt and an oxygen nucleophile (water or an alcohol), to form an organomercury intermediate. The intermediate’s carbon-mercury bond is then converted to a carbon-hydrogen bond by treatment with NaBH4
. The overall reaction coverts an alkene into an alcohol when the nucleophile is water, or an alkene into an ether when the nucleophile is an alcohol.
When phenols i.e. C6
OH is treated with CHCl3
(chloroform) in the presence of NaOH (sodium hydroxide), an aldehyde group (-CHO) is introduced at the ortho position of benzene ring leading to the formation of o-hydroxybenzaldehyde. The reaction is popularly known as Reimer Tiemann reaction.
Phenol reacts with sodium hydroxide to give sodium phenoxide which then reacts with carbon dioxide in acidic medium to give hydroxybenzoic acid.
Williamson ether synthesis:
The Williamson ether synthesis is an organic reaction used to convert an alcohol and an alkyl halide to an ether using a base such as NaOH.
Chapter 12 Aldehydes, ketones and carboxylic acids
The catalytic hydrogenation of acid chlorides allows the formation of aldehydes.
An alkyl or aryl cyanide dissolved in ether is reduced with stannous chloride and HCl to give aliphatic or aromatic aldehydes. The reaction proceeds by the formation of aldimine hydrochloride (present as stannichloride), which are not stable and hydrolyse to give aldehydes.
The Étard reaction is a chemical reaction that involves the direct oxidation of an aromatic or heterocyclic bound methyl group to an aldehyde using chromyl chloride. For example, toluene can be oxidized to benzaldehyde. It is named for the French chemist Alexandre Léon Étard.
Gatterman – Koch reaction:
When Benzene or its derivative is treated with Carbon Monoxide (CO) and Hydrogen Chloride (HCl) in the presence of Anhydrous AlCl3
or CuCl, it gives Benzaldehyde or substituted benzaldehyde.
The reaction of aldehydes and ketones with zinc amalgam (Zn/Hg alloy) in concentrated hydrochloric acid, which reduces the aldehyde or ketone to a hydrocarbon, is called Clemmensen reduction. Clemmensen reduction is one of the most powerful reduction methods in organic synthesis
Wolff Kishner Reduction:
Aldehydes and ketones can be converted to a hydrazine derivative by reaction with hydrazine. These “hydrazones” can be further converted to the corresponding alkane by reaction with base and heat. These two steps can be combined into one reaction called the Wolff-Kishner Reduction which represents a general method for converting aldehydes and ketones into alkanes.
Heating an aldehyde with fresh prepared ammoniacal silver nitrate solution produces a bright silver mirror due to the formation of silver metal.
Fehling’s solution A (aqueous copper sulfate) and Fehling solution B (alkaline sodium potassium tartrate) are mixed in equal amounts before the test. A reddish brown precipitate is obtained when an aldehyde is heated with Fehling’s reagent.
Aldol and Ketol lose water to provide α,β-unsaturated carbonyl compounds which are aldol condensation products.
Cross aldol condensation:
Aldol condensation is carried out between two different aldehydes and ketones. It gives a mixture of four products if both of them includes α-hydrogen atoms.
Aldehydes without α-hydrogen atom undergo self-oxidation and reduction reaction when prepared with concentrated alkali.
in Kolbe electrolysis, An aqueous solution of sodium or potassium salt of a carboxylic acid gives alkane containing an even number of carbon atoms on electrolysis.
Hell-Volhard-Zelinsky (HVZ )reaction:
Carboxylic acids having an α-hydrogen are halogenated at the α-position on treatment with chlorine (Cl) or bromine (Br) in the presence of small amount of red phosphorus to give α-halocarboxylic acid. This reaction is known as HELL – VOLHARD ZELINSKY (HVZ) REACTION.
Chapter 13 Compounds Containing Nitrogen
Primary amine (both aliphatic and aromatic) when warmed with chloroform and alcoholic KOH, gives isocyanides (carbylamines). This is called carbylamine reaction. Carbylamines has an offensive smell. This reaction is answered only by primary amine and hence to distinguish primary amine from other classes of amines.
Hoffmann bromamide degradation reaction:
When a Primary AMIDE is treated with an Aqueous or Alcoholic NaOH (SODIUM HYDROXIDE) or KOH (POTASSIUM HYDROXIDE) solution and BROMINE, it gives a Primary AMINE which has one CARBON atom less than the original AMIDE.
Gabriel phthalimide synthesis:
Phthalimide prepared with Ethanolic Potassium Hydroxide produces Potassium salt of Phthalimide when heated with Alkyl Halide followed by Alkaline hydrolysis forms the corresponding primary Amine.
The conversion of aryl amines to aryl fluorides via diazotisation and subsequent thermal decomposition of the derived tetrafluoroborates or hexafluorophosphates. The decomposition may also be induced photochemically.
The Sandmeyer reaction is a chemical reaction used to synthesize aryl halides from aryl diazonium salts using copper salts as reagents or catalysts. It is an example of a radical-nucleophilic aromatic substitution
The Gattermann reaction, (also known as the Gattermann aldehyde synthesis) is a chemical reaction in which aromatic compounds are formylated by hydrogen cyanide in the presence of a Friedel -Crafts catalyst (e.g. AlCl3
This Reaction is same as SANDMEYER REACTION. But the only difference between both of them is that here we use COPPER POWDER (Cu) in the presence of HCl/HBr, and in SANDMEYER REACTION we use Cu2Cl2/Cu2Br2as catalyst.
Benzenesulfonyl chloride (C6
Cl) reacts with primary and secondary amines to produce sulphonamides.
Benzene diazonium chloride gets reacted with phenol in which the phenol molecule at its para position is mixed with the diazonium salt to give p-hydroxyazobenzene.
To know more about Chemical Reactions in detail, [Follow ##eye##]
Name Reactions Asked in CBSE & IIT JEE Exams
All name reactions of chemistry class 12th cbse & isc
CBSE Chemistry Class XII Important Name Reaction
Most important name reactions in organic chemistry
I hope you find it helpful. Don’t forget to share. Stay connected for more. You can also follow: JEE/NEET/AIIMS aspirants for more material and other helpful topics related to the JEE/ NEET. All the Best!