Definitions [18]
Define Enantiomers.
Stereoisomers which are non-superimposable mirror images of each other and rotate the plane of plane polarised light through the same angle but in opposite directions are known as enantiomers or enatiomorphs.
Define racemic mixture.
A mixture containing two enantiomers in equal proportions will have zero optical rotation, as the rotation due to one isomer will be cancelled by the rotation due to the other isomer. Such a mixture is called a racemic mixture or a racemic modification.
The alkyl halide in which halogen is attached to a primary carbon atom is called primary alkyl halide.
The reaction in which diazonium salt is treated with cuprous halide to form haloarene is called Sandmeyer reaction.
The reaction in which halogen is added across a carbon-carbon double bond is called halogenation reaction.
The reaction in which alkyl chloride or bromide is converted into alkyl fluoride using metallic fluorides is called Swarts reaction.
The formation of equal amounts of two enantiomers resulting in optically inactive mixture is called racemisation.
The organic compounds in which one or more hydrogen atoms of hydrocarbons are replaced by halogen atoms are called halogen derivatives.
The compounds in which halogen atom is bonded to an sp³ hybridised carbon atom of an alkyl group are called haloalkanes.
The compounds in which halogen atom is directly bonded to an sp² hybridised carbon atom of an aromatic ring are called haloarenes.
The alkyl halide in which halogen is attached to a secondary carbon atom is called secondary alkyl halide.
The alkyl halide in which halogen is attached to a tertiary carbon atom is called tertiary alkyl halide.
The compounds in which halogen is bonded to an sp³ carbon adjacent to a carbon-carbon double bond are called allylic halides.
The compounds in which halogen is bonded to an sp³ carbon attached to an aromatic ring are called benzylic halides.
The compounds in which halogen is bonded to an sp² carbon of a carbon-carbon double bond are called vinylic halides.
The reaction in which a halogen atom in an alkyl halide is replaced by a nucleophile is called nucleophilic substitution reaction.
The reaction in which a halogen atom is removed along with a hydrogen atom forming a double bond is called elimination reaction.
The reaction in which alkyl chloride or bromide reacts with sodium iodide in acetone to form alkyl iodide is called Finkelstein reaction.
Key Points
Statement:
Aryl halide reacts with alkyl halide in presence of sodium in dry ether forming alkyl arene.
Mechanism:
Free radical coupling reaction.
Limitation:
Mixture of products may form.
Statement:
Alkyl chlorides or bromides react with sodium iodide in dry acetone to form alkyl iodides.
Equation:
R–Cl + NaI → R–I + NaCl↓
Reason:
NaCl precipitates in acetone driving the reaction forward.
Statement:
Alkyl chlorides or bromides react with metallic fluorides (AgF, Hg₂F₂, CoF₂) to form alkyl fluorides.
Equation:
R–Cl + AgF → R–F + AgCl
Importance:
Used for preparation of alkyl fluorides.
Statement:
Aryl diazonium salts react with cuprous halide (CuCl/CuBr) to give haloarenes.
Equation:
Ar–N₂⁺Cl⁻ + CuCl → Ar–Cl + N₂
Importance:
Used to introduce halogen into aromatic ring.
- Halogen is more electronegative than carbon.
- Bond becomes polar.
- Carbon carries partial positive charge.
- Reactivity depends on bond strength.
- Generally colourless liquids or gases.
- Boiling point increases with molecular mass.
- Slightly soluble in water.
- Density increases with number of halogen atoms.
A bimolecular nucleophilic substitution reaction in which nucleophile attacks carbon from backside and displaces leaving group in a single step.
Characteristics:
- One-step reaction
- No intermediate
- Transition state formed
- Inversion of configuration
- Rate depends on both reactants
Order:
Methyl > 1° > 2° > 3°
Reason:
Steric hindrance affects reaction.
A unimolecular nucleophilic substitution reaction in which leaving group departs first forming carbocation intermediate.
Characteristics:
- Two-step reaction
- Carbocation intermediate
- Rate depends only on substrate
- Racemisation possible
- Favoured by 3° halides
Order:
3° > 2° > 1°
Reason:
Stability of carbocation.
Statement:
In elimination reactions, the preferred product is the alkene having greater number of alkyl groups attached to the doubly bonded carbon atoms.
Example:
2-Bromopentane → Pent-2-ene (major)
Reason:
More substituted alkene is more stable.
Statement:
Alkyl halides react with sodium metal in dry ether to form higher alkanes.
Reaction:
2R–X + 2Na → R–R + 2NaX
Limitation:
Best for primary alkyl halides.
Statement:
Alkyl halides react with magnesium in dry ether to form Grignard reagents (R–MgX).
Nature:
Highly reactive, reacts with water.
Important:
Reaction must be moisture free.
Important Questions [71]
- Why is Ch2 = Ch - Ch2 - Cl More Easily Hydrolysed than Ch3 - Ch2 - Ch2 - Cl ?
- How do you convert Chlorobenzene to biphenyl?
- Define Enantiomers.
- Which of the following belongs to the class of vinyl halides?
- Draw the Structure of Major Monohalo Product in Each of the Following Reactions :
- Write the Structures of the Main Products in the Following Reactions : - 2
- Write the Structure of 1-bromo-4-chlorobut-2-ene
- Write the mechanism (using curved arrow notation) of the following reaction:
- Out of Which is an Example of a Benzylic Halide?
- Write the Product(S) in the Following Reactions: O+Hcn
- Write the product(s) in the following reaction: COONa + NaOH ->[CaO][\Delta] ?
- Write the Product(S) in the Following Reactions: Ch3−Ch=Ch−Cn Dibal−H
- Complete the Following Reaction: \\Ce{(C6h5ch2)2cd + 2ch3cocl}\
- Define racemic mixture.
- Arrange the set of compounds in order of increasing boiling points. Bromomethane, Bromoform, Chloromethane, Dibromomethane.
- Arrange the following compounds in increasing order of their boiling points: CH3CH2OH, CH3−CHO, CH3−COOH
- Arrange the following compounds in increasing order of their boiling points. (a) CH3-CH(CH3)-CH2Br (b) CHA3CHA2CHA2CHA2Br
- P-Dichlorobenzene has higher m.p. and lower solubility than those of o- and m-isomers. Discuss.
- Why is the boiling point of o-dichlorobenzene higher than p-dichlorobenzene, but the melting point of para-isomer is higher than ortho-isomer?
- Give Reasons : N-butyl Bromide Has Higher Boiling Point than T-butyl Bromide.
- Why Dextro and Laevorotatory Isomers of Butan-2-ol Are Difficult to Separate by Fractional Distillation?
- Which Would Undergo Sn1 Reaction Faster in the Following Pair and Why?
- Write the Structure of an Isomer of Compound C4h9br Which is Most Reactive Towards Sn1 Reaction
- Write the Major Products(S) in the Following
- How the following conversion can be carried out? Ethanol to propanenitrile
- Write the main products when methyl chloride is treated with AgCN.
- Give reasons for the following: (CH3)3C–O–CH3 on reaction with HI gives (CH3)3C–I and CH3–OH as the main products and not (CH3)3C–OH and CH3–I.
- which is more reactive towards SN1 reaction and why?
- Given reasons: C–Cl bond length in chlorobenzene is shorter than C–Cl bond length in CH3–Cl.
- Which Would Undergo SN2 Reaction Faster in the Following Pair and Why?
- Write the Structure of the Major Product in Each of the Following Reaction
- Write the Structures of A, B and C in the Following
- In the following pair of halogen compounds, which compound undergoes a faster SN1 reaction? Cl and Cl
- What are ambident nucleophiles? Explain with an example.
- Arrange the compounds of the following set in order of reactivity towards SN2 displacement: 2-Bromo-2-methylbutane, 1-Bromopentane, 2-Bromopentane
- What happens when ethyl chloride is treated with aqueous KOH?
- C–Cl bond length in chlorobenzene is shorter than C–Cl bond length in CH3–Cl.
- Sn1 Reactions Are Accompanied by Racemization in Optically Active Alkyl Halides.
- Given Reasons: Sn1 Reactions Are Accompanied by Racemization in Optically Active Alkyl Halides.
- Which Would Undergo Sn2 Reaction Faster in the Following Pair and Why ? Ch3 – Ch2 – Br and Ch3 – Ch2 – I
- Answer the Following Question. Write One Stereochemical Difference Between Sn1 and Sn2 Reactions.
- Racemisation occurs in ______.
- Assertion (A) : Nucleophilic substitution of iodoethane is easier than chloroethane. Reason (R) : Bond enthalpy of C-I bond is less than that of C-Cl bond.
- Arrange the following compounds in increasing order of reactivity towards SN2 reaction. 2-Bromopentane, 1-Bromopentane, 2-Bromo-2-methylbutane
- Retention of configuration is observed in ______.
- Inversion of configuration occurs in ______.
- Complete the reaction with the main product formed: N2+Cl- ->[CH3CH2OH]
- Convert bromoethane to propanamine.
- Give the mechanism of the following reaction: CHA3CHA2OH→413KHA2SOA4CHA3CHA2−O−CHA2CHA3+HA2O
- Nucleophilic Substitution: Nucleophilic substitution reaction of haloalkane can be conducted according to both SN1 and SN2 mechanisms. SN1 is a two-step reaction, while SN2 is a single-step reaction.
- What happens when n-butyl chloride is treated with alcoholic KOH?
- How do you convert: 2-bromobutane to but-2-ene
- The conversion of an alkyl halide into an alkene by alcoholic KOH is classified as ______.
- Write the Structure of Main Compounds a and B in the Following Reaction:
- Write the final product(s) in each of the following reactions
- What happens when CHA3−Br is treated with KCN?
- Why haloarenes are not reactive towards nucleophilic substitution reaction? Give two reactions.
- Assertion: Chlorobenzene is resistant to nucleophilic substitution reaction at room temperature. Reason (R): C–Cl bond gets weaker due, to resonance.
- Chlorobenzene is extremely less reactive towards a nucleophilic substitution reaction. Give two reasons for the same.
- Give reasons: The dipole moment of chlorobenzene is lower than that of cyclohexyl chloride.
- Write the Product Formed on Reaction of D-glucose with Br2 Water.
- The presence of nitro group (−NO2) at o/p positions increases the reactivity of haloarenes towards nucleophilic substitution reactions.
- Write Chemical Equation in Support of Your Answer. Out of Cl and Ch2- Cl, Which One is More Reactive Towards Nucleophilic Substitution Reaction and Why?
- Out of (Ch3)3 C-br and (Ch3)3 C-i, Which One is More Reactive Towards Sn1 and Why?
- Assertion (A): Chlorobenzene is resistant to electrophilic substitution reaction. Reason (R): C-Cl bond in chlorobenzene acquires partial double bond characters due to resonance.
- How Would You Account the Following : Transition Metals and Their Compounds Show Catalytic Properties.
- Write the Major Products(S) in the Following
- Auto-oxidation of chloroform in air and sunlight produces a poisonous gas known as ______.
- Write the equation for the following: Oxidation of chloroform by air and light.
- Give Reasons : Racemic Mixture is Optically Inactive.
- Identify the Chiral Molecule in the Following Pair
Concepts [17]
- Introduction of Haloalkanes and Haloarenes
- Classification of Haloalkanes and Haloarenes
- Nomenclature
- Nature of C-X Bond
- Methods of Preparation of Haloalkanes
- Methods of Preparation of Haloarenes
- Physical Properties of Haloalkanes and Haloarenes
- Reactions of Haloalkanes - Nucleophilic Substitution Reactions
- Reactions of Haloalkanes - Elimination Reactions
- Reactions of Haloalkanes - Reaction with Metals
- Reactions of Haloarenes - Nucleophilic Substitution
- Reactions of Haloarenes - Electrophilic Substitution Reactions
- Reactions of Haloarenes - Reaction with Metals
- Polyhalogen Compounds
- R-s and D-l Configuration
- Haloalkanes and Haloarenes Numericals
- Overview of Haloalkanes and Haloarenes
