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Derivatives of Alkanes
The compounds formed by the replacement of one or more
hydrogen atoms of alkanes by halogen atoms are
called halogen derivatives of alkanes.
Examples: CH3Cl (methyl chloride), C2H5
Br (ethyl bromide)
derivatives of alkanes
one halogen atom
two halogen atoms
three halogen atoms
four halogen atoms
They are also called alkyl halides. Their general formula is CnH2n+1
X where X = Cl, Br or I. They are also
represented as R - X, where R stands for an alkyl group.
Nomenclature according to:
Common system - alkyl halide
IUPAC system - haloalkane
of Monohalogen Derivatives of Alkanes or Alkyl Halides
Alkyl halides are classified into the following three classes depending
on the number of alkyl groups attached to the carbon atom bearing the
Halogenation is a
substitution reaction. The order of reactivity of halogens is
F2 > Cl2 > Br2 > I2
It is an addition reaction.
of Alkyl Halides
As the electronegativity difference between the
carbon and halogen atoms is high, alkyl halides are highly polar in nature.
The order of reactivity of alkyl halides is: Tertiary > Secondary >
Carbonium ion (Carbocation)
is an organic species in which the carbon atom carries a positive
is an organic species in which the carbon atom carries a negative
is an electron deficient species.
is an electron rich species.
is a planar ion.
is a tetrahedral ion.
carbon atom involved is sp2- hybridised.
carbon atom involved is sp3 - hybridised.
Example: - : CH3
of stability is: 3° > 2° > 1° > CH3-
of stability is: CH3-> 1° > 2° > 3°
atom has 6 electrons.
atom has 8 electrons.
electrophile is an electron-deficient
nucleophile is an electron rich species.
attacks an electron rich centre of the substrate. Examples: H+,
CH3+, R+, Lewis acids.
attacks an electron deficient centre of the substrate. Examples: OH-, Cl-, RCOO-, Lewis bases.
polarisation of a single (s) covalent bond due to the
electronegativity difference between the
atoms joined by it is called inductive effect.
shift of the p-bond electrons in a double
bond to one of the atoms joined by it in the presence of a suitable
reagent is called electromeric effect.
is present in a s-bond.
is possible only in a p-bond.
is a permanent effect.
is a temporary effect.