The reaction when hydrogen chloride reacts with 2-methyl-1,3-butadiene to form 1-chloro-3-methyl-2-butene as a major product via 1,4-addition mechanism and no product formed by 1,2-additon, is to be explained. Concept introduction: 舧 Electrophiles are electron-deficient species, which has positive or partially positive charge. Lewis acids are electrophiles, which accept electron pair. 舧 Nucleophiles are electron rich species, which has negative or partially negative charge. Lewis bases are nucleophiles, which donate electron pair. 舧 Free radical is an atom, molecule or ion that has an unpaired electron, which makes it highly chemically reactive. 舧 Substitution reaction: A reaction in which one of the hydrogen atoms of a hydrocarbon or a functional group is substituted by any other functional group is called substitution reaction. 舧 Elimination reaction: A reaction in which two substituent groups are detached and a double bond is formed is called elimination reaction. 舧 Addition reaction: It is the reaction in which unsaturated bonds are converted to saturated molecules by the addition of molecules. 舧 The reaction in which there is addition of hydrogen molecule is called hydrogenation reaction. 舧 H 2 /Pt is a reducing agent, which reduces alkynes to alkanes. 舧 Hydrogenation with platinum as a catalyst is used to convert unsaturated carbohydrates to saturated hydrocarbons 舧 Oxidation of alkenes with ozone in the presence of dimethyl sulphate results in the formation of ketones or aldehydes , depending on the orientation and position of the double bond. 舧 Ozonolysis helps convert the carbon–carbon double bonds to carbon–oxygen double bond (carbonyl compounds). 舧 Dimethyl sulfide is used as a reducing agent that decomposes the intermediate formed into the carbonyl group. 舧 NBS (nitro-bromo succinimide) is a special reagent used for bromination of allylic carbocations. 舧 Bromine replaces the hydrogen attached to the carbon adjacent to the carbon bearing double bond. 舧 This method of using NBS can produce allylic bromides without bromine reacting with the double bond. 舧 Dehydration of a primary alcohol in the presence of a mineral acid like concentrated sulfuric acid results in the formation of alkene via E2 elimination. 舧 The stability of carbocation: tertiary carbocation>secondary carbocation>primary carbocation > 舧 The 1,2 – addition to a diene is the addition of an electrophile to the carbon designated as 1 and a nucleophile to the carbon designated as 2. The positions of carbons as 1 and 2 are not according to the IUPAC numbering of the molecule, but as a conjugated diene molecule. 1,4-addition results in addition of hydrogen to thee carbon designated as 1 and a halogen to the carbon designated as 4. 舧 The mechanism of 1,2 addition and 1,4-addition of hydro halogenation is given below:

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Chapter 13, Problem 25P

Interpretation Introduction

Interpretation:

The reaction when hydrogen chloride reacts with 2-methyl-1,3-butadiene to form 1-chloro-3-methyl-2-butene as a major product via 1,4-addition mechanism and no product formed by 1,2-additon, is to be explained.

Concept introduction:

舧 Electrophiles are electron-deficient species, which has positive or partially positive charge. Lewis acids are electrophiles, which accept electron pair.

舧 Nucleophiles are electron rich species, which has negative or partially negative charge. Lewis bases are nucleophiles, which donate electron pair.

舧 Free radical is an atom, molecule or ion that has an unpaired electron, which makes it highly chemically reactive.

舧 Substitution reaction: A reaction in which one of the hydrogen atoms of a hydrocarbon or a functional group is substituted by any other functional group is called substitution reaction.

舧 Elimination reaction: A reaction in which two substituent groups are detached and a double bond is formed is called elimination reaction.

舧 Addition reaction: It is the reaction in which unsaturated bonds are converted to saturated molecules by the addition of molecules.

舧 The reaction in which there is addition of hydrogen molecule is called hydrogenation reaction.

舧 H2/Pt is a reducing agent, which reduces alkynes to alkanes.

舧 Hydrogenation with platinum as a catalyst is used to convert unsaturated carbohydrates to saturated hydrocarbons

舧 Oxidation of alkenes with ozone in the presence of dimethyl sulphate results in the formation of ketones or aldehydes, depending on the orientation and position of the double bond.

舧 Ozonolysis helps convert the carbon–carbon double bonds to carbon–oxygen double bond (carbonyl compounds).

舧 Dimethyl sulfide is used as a reducing agent that decomposes the intermediate formed into the carbonyl group.

舧 NBS (nitro-bromo succinimide) is a special reagent used for bromination of allylic carbocations.

舧 Bromine replaces the hydrogen attached to the carbon adjacent to the carbon bearing double bond.

舧 This method of using NBS can produce allylic bromides without bromine reacting with the double bond.

舧 Dehydration of a primary alcohol in the presence of a mineral acid like concentrated sulfuric acid results in the formation of alkene via E2 elimination.

舧 The stability of carbocation: tertiary carbocation>secondary carbocation>primary carbocation >

舧 The 1,2 – addition to a diene is the addition of an electrophile to the carbon designated as 1 and a nucleophile to the carbon designated as 2. The positions of carbons as 1 and 2 are not according to the IUPAC numbering of the molecule, but as a conjugated diene molecule. 1,4-addition results in addition of hydrogen to thee carbon designated as 1 and a halogen to the carbon designated as 4.

舧 The mechanism of 1,2 addition and 1,4-addition of hydro halogenation is given below:

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