• Skip to main content
  • Skip to primary sidebar
  • Skip to footer
  • NCERT Solutions
    • NCERT Books Free Download
  • TS Grewal
    • TS Grewal Class 12 Accountancy Solutions
    • TS Grewal Class 11 Accountancy Solutions
  • CBSE Sample Papers
  • NCERT Exemplar Problems
  • English Grammar
  • MCQ Questions

CBSE Tuts

CBSE Maths notes, CBSE physics notes, CBSE chemistry notes

NEET Chemistry Notes Haloalkanes and Haloarenes – Preparation of Aryl Halides

NEET Chemistry Notes Haloalkanes and Haloarenes – Preparation of Aryl Halides

 Preparation of Aryl Halides

Preparation of Aryl Halides
(Haloarenes)
These are prepared by the following methods:

  • By Electrophilic Substitution of Arenes

It is carried out in the presence of a halogen carrier (i.e. Lewis acid) likeFeCl3,FeBr3 in dark and at low temperature.
NEET Chemistry Notes Haloalkanes and Haloarenes - Preparation of Aryl Halides 1

Sandmeyer’s Reaction

In this reaction, benzene diazonium chloride is warmed with cuprous chloride/bromide in HCl to obtain chloro/bromo arenes.
NEET Chemistry Notes Haloalkanes and Haloarenes - Preparation of Aryl Halides 2
NEET Chemistry Notes Haloalkanes and Haloarenes - Preparation of Aryl Halides 3
Borodine-Hunsdiecker reaction (used to produce alkyl bromide) proceeds through free radical mechanism and is used to reduce the length of carbon chain.

Physical Properties of Haloalkanes and Haloarenes

The physical properties of alkyl halides and aryl halides are given below:

Boiling and Melting Point

  • Alkyl halides and haloarenes are polar compounds and have higher boiling point due to dipole-dipole interaction. Alkyl/aryl halides have higher boiling point than hydrocarbons of comparable molecular mass.
  •  Decreasing order of boiling point of alkyl halides is as, Rl> RBT> RCA> RF
    This is because with the increase in size and mass of halogen atom, the magnitude of van der Waals’ forces increases.
  • Straight chain alkyl halides have higher boiling point as compared with branched chain alkyl halide of similar molecular weight, hence boiling points of isomeric haloalkanes decrease with increase in branching due to decrease in surface area, e.g.
    NEET Chemistry Notes Haloalkanes and Haloarenes - Preparation of Aryl Halides 4
    NEET Chemistry Notes Haloalkanes and Haloarenes - Preparation of Aryl Halides 5
  • The para isomers of dihalobenzenes has high melting point as compared to their ortho and meta isomers. It is due to symmetry of para isomers that fits in crystal lattice as compared to ortho and meta isomers.
    NEET Chemistry Notes Haloalkanes and Haloarenes - Preparation of Aryl Halides 6

Density and Solubility

Bromo and iodo derivatives of hydrocarbons are heavier than water.
Lower haloalkanes are very slightly soluble in water but others are insoluble in water because haloalkanes/ haloarenes do not form hydrogen bond with water.

Chemical Properties of Haloalkanes

Haloalkanes are highly reactive compounds due to the presence of polar R—X bond. The reactions of haloalkanes may be of two types. These are nucleophilic substitution reactions and elimination reactions.

Nucleophilic Substitution Reactions

In haloalkanes, these reactions proceed either by SN 1 or by SN 2 type of mechanism.

 Nucleophilic Substitution Unimolecular Reaction (SN1)

  • It follows first order kinetics, rate = k [substrate],
  • Reaction is completed in two steps.
  • Carbocation is formed and gets rearranged, if possible.
  • Nucleophile can attack from front and back side. Therefore, racemic mixture can be formed.
  • Tertiary alkyl group and polar solvent favour SN 1
    NEET Chemistry Notes Haloalkanes and Haloarenes - Preparation of Aryl Halides 7

Nucleophilic Substitution Bimolecular Reaction (SN 2)

  •  It follows second order kinetics, rate = k [substrate] [nucleophile]
  •  Reaction is completed in one step.
  • Transition is formed.
  •  It involves complete inversion in configuration as the attack of the nucleophile occurs from the back side of reactant, e.g.
    NEET Chemistry Notes Haloalkanes and Haloarenes - Preparation of Aryl Halides 8
  • Primary alkyl group and non-polar solvent favour SN 2
  •  Reactivity of halides towards SN 2mechanism is 1° > 2° > 3° > neo-pentyl halides.
  • In SN 2 mechanism, rate of reaction does not depend upon the strength of attacking nucleophile.
    The strength of different nucleophiles isNEET Chemistry Notes Haloalkanes and Haloarenes - Preparation of Aryl Halides 9.

ChemistryPhysicsBiology

Primary Sidebar

NCERT Exemplar problems With Solutions CBSE Previous Year Questions with Solutoins CBSE Sample Papers

Recent Posts

  • MCQ Questions with Answers for Class 12, 11, 10, 9, 8, 7, 6, 5, 4, 3, 2, and 1 all Subjects
  • Angle, Types of Angles
  • AND gate is formed by using two? 1)OR 2)NAND 3)NOT 4)NOR
  • And expression for one minus the quotient of one and a number X?
  • What is average human body temperature in Kelvins?
  • How many moles of caffeine are in a cup, and how many molecules of caffeine?
  • How far will the car have traveled in that time?
  • What is its atomic number?
  • How many neutrons does it have?
  • An atom loses electrons to form what?
  • What is the atomic number of this atom?
  • Which one of these is the answer?
  • What is its concentration?
  • Can an equilateral triangle also be isosceles?
  • What is the charge of an alpha particle?

Footer

Maths NCERT Solutions

NCERT Solutions for Class 12 Maths
NCERT Solutions for Class 11 Maths
NCERT Solutions for Class 10 Maths
NCERT Solutions for Class 9 Maths
NCERT Solutions for Class 8 Maths
NCERT Solutions for Class 7 Maths
NCERT Solutions for Class 6 Maths

SCIENCE NCERT SOLUTIONS

NCERT Solutions for Class 12 Physics
NCERT Solutions for Class 12 Chemistry
NCERT Solutions for Class 11 Physics
NCERT Solutions for Class 11 Chemistry
NCERT Solutions for Class 10 Science
NCERT Solutions for Class 9 Science
NCERT Solutions for Class 7 Science
MCQ Questions NCERT Solutions
CBSE Sample Papers
cbse ncert
NCERT Exemplar Solutions LCM and GCF Calculator
TS Grewal Accountancy Class 12 Solutions
TS Grewal Accountancy Class 11 Solutions