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1 | 5605-5608 | Can you think of the reason why it
happens Actually the carbocation formed in the slow step being sp
2
hybridised is planar (achiral) The attack of the nucleophile may be
accomplished from either side of the plane of carbocation resulting in
a mixture of products, one having the same configuration (the –OH
attaching on the same position as halide ion) and the other having
opposite configuration (the –OH attaching on the side opposite to halide
ion) This may be illustrated by hydrolysis of optically active
2-bromobutane, which results in the formation of (±)-butan-2-ol |
1 | 5606-5609 | Actually the carbocation formed in the slow step being sp
2
hybridised is planar (achiral) The attack of the nucleophile may be
accomplished from either side of the plane of carbocation resulting in
a mixture of products, one having the same configuration (the –OH
attaching on the same position as halide ion) and the other having
opposite configuration (the –OH attaching on the side opposite to halide
ion) This may be illustrated by hydrolysis of optically active
2-bromobutane, which results in the formation of (±)-butan-2-ol 2 |
1 | 5607-5610 | The attack of the nucleophile may be
accomplished from either side of the plane of carbocation resulting in
a mixture of products, one having the same configuration (the –OH
attaching on the same position as halide ion) and the other having
opposite configuration (the –OH attaching on the side opposite to halide
ion) This may be illustrated by hydrolysis of optically active
2-bromobutane, which results in the formation of (±)-butan-2-ol 2 Elimination reactions
When a haloalkane with b-hydrogen atom is heated with alcoholic
solution of potassium hydroxide, there is elimination of hydrogen
atom from b-carbon and a halogen atom from the a-carbon atom |
1 | 5608-5611 | This may be illustrated by hydrolysis of optically active
2-bromobutane, which results in the formation of (±)-butan-2-ol 2 Elimination reactions
When a haloalkane with b-hydrogen atom is heated with alcoholic
solution of potassium hydroxide, there is elimination of hydrogen
atom from b-carbon and a halogen atom from the a-carbon atom Location of aaaaa and
bbbbb carbon in a
molecule
Carbon on which
halogen atom is
directly attached is
called a-carbon and
the carbon atom
adjacent to this
carbon is called
b-carbon |
1 | 5609-5612 | 2 Elimination reactions
When a haloalkane with b-hydrogen atom is heated with alcoholic
solution of potassium hydroxide, there is elimination of hydrogen
atom from b-carbon and a halogen atom from the a-carbon atom Location of aaaaa and
bbbbb carbon in a
molecule
Carbon on which
halogen atom is
directly attached is
called a-carbon and
the carbon atom
adjacent to this
carbon is called
b-carbon Rationalised 2023-24
180
Chemistry
As a result, an alkene is formed as a product |
1 | 5610-5613 | Elimination reactions
When a haloalkane with b-hydrogen atom is heated with alcoholic
solution of potassium hydroxide, there is elimination of hydrogen
atom from b-carbon and a halogen atom from the a-carbon atom Location of aaaaa and
bbbbb carbon in a
molecule
Carbon on which
halogen atom is
directly attached is
called a-carbon and
the carbon atom
adjacent to this
carbon is called
b-carbon Rationalised 2023-24
180
Chemistry
As a result, an alkene is formed as a product Since b-hydrogen
atom is involved in elimination, it is often called bbbbb-elimination |
1 | 5611-5614 | Location of aaaaa and
bbbbb carbon in a
molecule
Carbon on which
halogen atom is
directly attached is
called a-carbon and
the carbon atom
adjacent to this
carbon is called
b-carbon Rationalised 2023-24
180
Chemistry
As a result, an alkene is formed as a product Since b-hydrogen
atom is involved in elimination, it is often called bbbbb-elimination If there is possibility of formation of more than one alkene due to
the availability of more than one b-hydrogen atoms, usually one alkene
is formed as the major product |
1 | 5612-5615 | Rationalised 2023-24
180
Chemistry
As a result, an alkene is formed as a product Since b-hydrogen
atom is involved in elimination, it is often called bbbbb-elimination If there is possibility of formation of more than one alkene due to
the availability of more than one b-hydrogen atoms, usually one alkene
is formed as the major product These form part of a pattern first
observed by Russian chemist, Alexander Zaitsev (also pronounced as
Saytzeff) who in 1875 formulated a rule which can be summarised as
“in dehydrohalogenation reactions, the preferred product is that
alkene which has the greater number of alkyl groups attached to the
doubly bonded carbon atoms |
1 | 5613-5616 | Since b-hydrogen
atom is involved in elimination, it is often called bbbbb-elimination If there is possibility of formation of more than one alkene due to
the availability of more than one b-hydrogen atoms, usually one alkene
is formed as the major product These form part of a pattern first
observed by Russian chemist, Alexander Zaitsev (also pronounced as
Saytzeff) who in 1875 formulated a rule which can be summarised as
“in dehydrohalogenation reactions, the preferred product is that
alkene which has the greater number of alkyl groups attached to the
doubly bonded carbon atoms ” Thus, 2-bromopentane gives
pent-2-ene as the major product |
1 | 5614-5617 | If there is possibility of formation of more than one alkene due to
the availability of more than one b-hydrogen atoms, usually one alkene
is formed as the major product These form part of a pattern first
observed by Russian chemist, Alexander Zaitsev (also pronounced as
Saytzeff) who in 1875 formulated a rule which can be summarised as
“in dehydrohalogenation reactions, the preferred product is that
alkene which has the greater number of alkyl groups attached to the
doubly bonded carbon atoms ” Thus, 2-bromopentane gives
pent-2-ene as the major product 3 |
1 | 5615-5618 | These form part of a pattern first
observed by Russian chemist, Alexander Zaitsev (also pronounced as
Saytzeff) who in 1875 formulated a rule which can be summarised as
“in dehydrohalogenation reactions, the preferred product is that
alkene which has the greater number of alkyl groups attached to the
doubly bonded carbon atoms ” Thus, 2-bromopentane gives
pent-2-ene as the major product 3 Reaction with metals
Most organic chlorides, bromides and iodides react with certain
metals to give compounds containing carbon-metal bonds |
1 | 5616-5619 | ” Thus, 2-bromopentane gives
pent-2-ene as the major product 3 Reaction with metals
Most organic chlorides, bromides and iodides react with certain
metals to give compounds containing carbon-metal bonds Such
compounds are known as organo-metallic compounds |
1 | 5617-5620 | 3 Reaction with metals
Most organic chlorides, bromides and iodides react with certain
metals to give compounds containing carbon-metal bonds Such
compounds are known as organo-metallic compounds An
important class of organo-metallic compounds discovered by Victor
Grignard in 1900 is alkyl magnesium halide, RMgX, referred as
Grignard Reagents |
1 | 5618-5621 | Reaction with metals
Most organic chlorides, bromides and iodides react with certain
metals to give compounds containing carbon-metal bonds Such
compounds are known as organo-metallic compounds An
important class of organo-metallic compounds discovered by Victor
Grignard in 1900 is alkyl magnesium halide, RMgX, referred as
Grignard Reagents These reagents are obtained by the reaction of
haloalkanes with magnesium metal in dry ether |
1 | 5619-5622 | Such
compounds are known as organo-metallic compounds An
important class of organo-metallic compounds discovered by Victor
Grignard in 1900 is alkyl magnesium halide, RMgX, referred as
Grignard Reagents These reagents are obtained by the reaction of
haloalkanes with magnesium metal in dry ether A chemical reaction is the result of competition; it is a race that is won by the fastest
runner |
1 | 5620-5623 | An
important class of organo-metallic compounds discovered by Victor
Grignard in 1900 is alkyl magnesium halide, RMgX, referred as
Grignard Reagents These reagents are obtained by the reaction of
haloalkanes with magnesium metal in dry ether A chemical reaction is the result of competition; it is a race that is won by the fastest
runner A collection of molecules tend to do, by and large, what is easiest for them |
1 | 5621-5624 | These reagents are obtained by the reaction of
haloalkanes with magnesium metal in dry ether A chemical reaction is the result of competition; it is a race that is won by the fastest
runner A collection of molecules tend to do, by and large, what is easiest for them An
alkyl halide with b-hydrogen atoms when reacted with a base or a nucleophile has two
competing routes: substitution (SN1 and SN2) and elimination |
1 | 5622-5625 | A chemical reaction is the result of competition; it is a race that is won by the fastest
runner A collection of molecules tend to do, by and large, what is easiest for them An
alkyl halide with b-hydrogen atoms when reacted with a base or a nucleophile has two
competing routes: substitution (SN1 and SN2) and elimination Which route will be taken
up depends upon the nature of alkyl halide, strength and size of base/nucleophile and
reaction conditions |
1 | 5623-5626 | A collection of molecules tend to do, by and large, what is easiest for them An
alkyl halide with b-hydrogen atoms when reacted with a base or a nucleophile has two
competing routes: substitution (SN1 and SN2) and elimination Which route will be taken
up depends upon the nature of alkyl halide, strength and size of base/nucleophile and
reaction conditions Thus, a bulkier nucleophile will prefer to act as a base and abstracts
a proton rather than approach a tetravalent carbon atom (steric reasons) and vice versa |
1 | 5624-5627 | An
alkyl halide with b-hydrogen atoms when reacted with a base or a nucleophile has two
competing routes: substitution (SN1 and SN2) and elimination Which route will be taken
up depends upon the nature of alkyl halide, strength and size of base/nucleophile and
reaction conditions Thus, a bulkier nucleophile will prefer to act as a base and abstracts
a proton rather than approach a tetravalent carbon atom (steric reasons) and vice versa Similarly, a primary alkyl halide will prefer a SN2 reaction, a secondary halide- SN2 or
elimination depending upon the strength of base/nucleophile and a tertiary halide- SN1 or
elimination depending upon the stability of carbocation or the more substituted alkene |
1 | 5625-5628 | Which route will be taken
up depends upon the nature of alkyl halide, strength and size of base/nucleophile and
reaction conditions Thus, a bulkier nucleophile will prefer to act as a base and abstracts
a proton rather than approach a tetravalent carbon atom (steric reasons) and vice versa Similarly, a primary alkyl halide will prefer a SN2 reaction, a secondary halide- SN2 or
elimination depending upon the strength of base/nucleophile and a tertiary halide- SN1 or
elimination depending upon the stability of carbocation or the more substituted alkene Elimination versus substitution
Elimination versus substitution
Elimination versus substitution
Elimination versus substitution
Elimination versus substitution
Rationalised 2023-24
181 Haloalkanes and Haloarenes
Victor Grignard had a strange start in academic life for a chemist - he
took a maths degree |
1 | 5626-5629 | Thus, a bulkier nucleophile will prefer to act as a base and abstracts
a proton rather than approach a tetravalent carbon atom (steric reasons) and vice versa Similarly, a primary alkyl halide will prefer a SN2 reaction, a secondary halide- SN2 or
elimination depending upon the strength of base/nucleophile and a tertiary halide- SN1 or
elimination depending upon the stability of carbocation or the more substituted alkene Elimination versus substitution
Elimination versus substitution
Elimination versus substitution
Elimination versus substitution
Elimination versus substitution
Rationalised 2023-24
181 Haloalkanes and Haloarenes
Victor Grignard had a strange start in academic life for a chemist - he
took a maths degree When he eventually switched to chemistry, it was
not to the mathematical province of physical chemistry but to organic
chemistry |
1 | 5627-5630 | Similarly, a primary alkyl halide will prefer a SN2 reaction, a secondary halide- SN2 or
elimination depending upon the strength of base/nucleophile and a tertiary halide- SN1 or
elimination depending upon the stability of carbocation or the more substituted alkene Elimination versus substitution
Elimination versus substitution
Elimination versus substitution
Elimination versus substitution
Elimination versus substitution
Rationalised 2023-24
181 Haloalkanes and Haloarenes
Victor Grignard had a strange start in academic life for a chemist - he
took a maths degree When he eventually switched to chemistry, it was
not to the mathematical province of physical chemistry but to organic
chemistry While attempting to find an efficient catalyst for the process
of methylation, he noted that Zn in diethyl ether had been used for this
purpose and wondered whether the Mg/ether combination might be
successful |
1 | 5628-5631 | Elimination versus substitution
Elimination versus substitution
Elimination versus substitution
Elimination versus substitution
Elimination versus substitution
Rationalised 2023-24
181 Haloalkanes and Haloarenes
Victor Grignard had a strange start in academic life for a chemist - he
took a maths degree When he eventually switched to chemistry, it was
not to the mathematical province of physical chemistry but to organic
chemistry While attempting to find an efficient catalyst for the process
of methylation, he noted that Zn in diethyl ether had been used for this
purpose and wondered whether the Mg/ether combination might be
successful Grignard reagents were first reported in 1900 and Grignard
used this work for his doctoral thesis in 1901 |
1 | 5629-5632 | When he eventually switched to chemistry, it was
not to the mathematical province of physical chemistry but to organic
chemistry While attempting to find an efficient catalyst for the process
of methylation, he noted that Zn in diethyl ether had been used for this
purpose and wondered whether the Mg/ether combination might be
successful Grignard reagents were first reported in 1900 and Grignard
used this work for his doctoral thesis in 1901 In 1910, Grignard obtained
a professorship at the University of Nancy and in 1912, he was awarded
the Nobel prize for Chemistry which he shared with Paul Sabatier who
had made advances in nickel catalysed hydrogenation |
1 | 5630-5633 | While attempting to find an efficient catalyst for the process
of methylation, he noted that Zn in diethyl ether had been used for this
purpose and wondered whether the Mg/ether combination might be
successful Grignard reagents were first reported in 1900 and Grignard
used this work for his doctoral thesis in 1901 In 1910, Grignard obtained
a professorship at the University of Nancy and in 1912, he was awarded
the Nobel prize for Chemistry which he shared with Paul Sabatier who
had made advances in nickel catalysed hydrogenation In the Grignard reagent, the carbon-magnesium bond is covalent
but highly polar, with carbon pulling electrons from electropositive
magnesium; the magnesium halogen bond is essentially ionic |
1 | 5631-5634 | Grignard reagents were first reported in 1900 and Grignard
used this work for his doctoral thesis in 1901 In 1910, Grignard obtained
a professorship at the University of Nancy and in 1912, he was awarded
the Nobel prize for Chemistry which he shared with Paul Sabatier who
had made advances in nickel catalysed hydrogenation In the Grignard reagent, the carbon-magnesium bond is covalent
but highly polar, with carbon pulling electrons from electropositive
magnesium; the magnesium halogen bond is essentially ionic Grignard reagents are highly reactive and react with any source of
proton to give hydrocarbons |
1 | 5632-5635 | In 1910, Grignard obtained
a professorship at the University of Nancy and in 1912, he was awarded
the Nobel prize for Chemistry which he shared with Paul Sabatier who
had made advances in nickel catalysed hydrogenation In the Grignard reagent, the carbon-magnesium bond is covalent
but highly polar, with carbon pulling electrons from electropositive
magnesium; the magnesium halogen bond is essentially ionic Grignard reagents are highly reactive and react with any source of
proton to give hydrocarbons Even water, alcohols, amines are sufficiently
acidic to convert them to corresponding hydrocarbons |
1 | 5633-5636 | In the Grignard reagent, the carbon-magnesium bond is covalent
but highly polar, with carbon pulling electrons from electropositive
magnesium; the magnesium halogen bond is essentially ionic Grignard reagents are highly reactive and react with any source of
proton to give hydrocarbons Even water, alcohols, amines are sufficiently
acidic to convert them to corresponding hydrocarbons It is therefore necessary to avoid even traces of moisture from a Grignard
reagent |
1 | 5634-5637 | Grignard reagents are highly reactive and react with any source of
proton to give hydrocarbons Even water, alcohols, amines are sufficiently
acidic to convert them to corresponding hydrocarbons It is therefore necessary to avoid even traces of moisture from a Grignard
reagent That is why reaction is carried out in dry ether |
1 | 5635-5638 | Even water, alcohols, amines are sufficiently
acidic to convert them to corresponding hydrocarbons It is therefore necessary to avoid even traces of moisture from a Grignard
reagent That is why reaction is carried out in dry ether On the other
hand, this could be considered as one of the methods for converting
halides to hydrocarbons |
1 | 5636-5639 | It is therefore necessary to avoid even traces of moisture from a Grignard
reagent That is why reaction is carried out in dry ether On the other
hand, this could be considered as one of the methods for converting
halides to hydrocarbons Wurtz reaction
Alkyl halides react with sodium in dry ether to give hydrocarbons
containing double the number of carbon atoms present in the halide |
1 | 5637-5640 | That is why reaction is carried out in dry ether On the other
hand, this could be considered as one of the methods for converting
halides to hydrocarbons Wurtz reaction
Alkyl halides react with sodium in dry ether to give hydrocarbons
containing double the number of carbon atoms present in the halide This reaction is known as Wurtz reaction |
1 | 5638-5641 | On the other
hand, this could be considered as one of the methods for converting
halides to hydrocarbons Wurtz reaction
Alkyl halides react with sodium in dry ether to give hydrocarbons
containing double the number of carbon atoms present in the halide This reaction is known as Wurtz reaction 1 |
1 | 5639-5642 | Wurtz reaction
Alkyl halides react with sodium in dry ether to give hydrocarbons
containing double the number of carbon atoms present in the halide This reaction is known as Wurtz reaction 1 Nucleophilic substitution
Aryl halides are extremely less reactive towards nucleophilic
substitution reactions due to the following reasons:
(i) Resonance effect : In haloarenes, the electron pairs on halogen
atom are in conjugation with p-electrons of the ring and the
following resonating structures are possible |
1 | 5640-5643 | This reaction is known as Wurtz reaction 1 Nucleophilic substitution
Aryl halides are extremely less reactive towards nucleophilic
substitution reactions due to the following reasons:
(i) Resonance effect : In haloarenes, the electron pairs on halogen
atom are in conjugation with p-electrons of the ring and the
following resonating structures are possible C—Cl bond acquires a partial double bond character due to
resonance |
1 | 5641-5644 | 1 Nucleophilic substitution
Aryl halides are extremely less reactive towards nucleophilic
substitution reactions due to the following reasons:
(i) Resonance effect : In haloarenes, the electron pairs on halogen
atom are in conjugation with p-electrons of the ring and the
following resonating structures are possible C—Cl bond acquires a partial double bond character due to
resonance As a result, the bond cleavage in haloarene is difficult
than haloalkane and therefore, they are less reactive towards
nucleophilic substitution reaction |
1 | 5642-5645 | Nucleophilic substitution
Aryl halides are extremely less reactive towards nucleophilic
substitution reactions due to the following reasons:
(i) Resonance effect : In haloarenes, the electron pairs on halogen
atom are in conjugation with p-electrons of the ring and the
following resonating structures are possible C—Cl bond acquires a partial double bond character due to
resonance As a result, the bond cleavage in haloarene is difficult
than haloalkane and therefore, they are less reactive towards
nucleophilic substitution reaction 6 |
1 | 5643-5646 | C—Cl bond acquires a partial double bond character due to
resonance As a result, the bond cleavage in haloarene is difficult
than haloalkane and therefore, they are less reactive towards
nucleophilic substitution reaction 6 7 |
1 | 5644-5647 | As a result, the bond cleavage in haloarene is difficult
than haloalkane and therefore, they are less reactive towards
nucleophilic substitution reaction 6 7 2 Reactions of
Haloarenes
Rationalised 2023-24
182
Chemistry
(ii) Difference in hybridisation of carbon atom in C—X bond: In
haloalkane, the carbon atom attached to halogen is sp3
hybridised while in case of haloarene, the carbon atom attached
to halogen is sp2-hybridised |
1 | 5645-5648 | 6 7 2 Reactions of
Haloarenes
Rationalised 2023-24
182
Chemistry
(ii) Difference in hybridisation of carbon atom in C—X bond: In
haloalkane, the carbon atom attached to halogen is sp3
hybridised while in case of haloarene, the carbon atom attached
to halogen is sp2-hybridised The sp2 hybridised carbon with a greater s-character is more
electronegative and can hold the electron pair of C—X bond
more tightly than sp3-hybridised carbon in haloalkane with
less s-chararcter |
1 | 5646-5649 | 7 2 Reactions of
Haloarenes
Rationalised 2023-24
182
Chemistry
(ii) Difference in hybridisation of carbon atom in C—X bond: In
haloalkane, the carbon atom attached to halogen is sp3
hybridised while in case of haloarene, the carbon atom attached
to halogen is sp2-hybridised The sp2 hybridised carbon with a greater s-character is more
electronegative and can hold the electron pair of C—X bond
more tightly than sp3-hybridised carbon in haloalkane with
less s-chararcter Thus, C—Cl bond length in haloalkane is
177pm while in haloarene is 169 pm |
1 | 5647-5650 | 2 Reactions of
Haloarenes
Rationalised 2023-24
182
Chemistry
(ii) Difference in hybridisation of carbon atom in C—X bond: In
haloalkane, the carbon atom attached to halogen is sp3
hybridised while in case of haloarene, the carbon atom attached
to halogen is sp2-hybridised The sp2 hybridised carbon with a greater s-character is more
electronegative and can hold the electron pair of C—X bond
more tightly than sp3-hybridised carbon in haloalkane with
less s-chararcter Thus, C—Cl bond length in haloalkane is
177pm while in haloarene is 169 pm Since it is difficult to
break a shorter bond than a longer bond, therefore, haloarenes
are less reactive than haloalkanes towards nucleophilic
substitution reaction |
1 | 5648-5651 | The sp2 hybridised carbon with a greater s-character is more
electronegative and can hold the electron pair of C—X bond
more tightly than sp3-hybridised carbon in haloalkane with
less s-chararcter Thus, C—Cl bond length in haloalkane is
177pm while in haloarene is 169 pm Since it is difficult to
break a shorter bond than a longer bond, therefore, haloarenes
are less reactive than haloalkanes towards nucleophilic
substitution reaction (iii) Instability of phenyl cation: In case of haloarenes, the phenyl
cation formed as a result of self-ionisation will not be stabilised
by resonance and therefore, SN1 mechanism is ruled out |
1 | 5649-5652 | Thus, C—Cl bond length in haloalkane is
177pm while in haloarene is 169 pm Since it is difficult to
break a shorter bond than a longer bond, therefore, haloarenes
are less reactive than haloalkanes towards nucleophilic
substitution reaction (iii) Instability of phenyl cation: In case of haloarenes, the phenyl
cation formed as a result of self-ionisation will not be stabilised
by resonance and therefore, SN1 mechanism is ruled out (iv) Because of the possible repulsion, it is less likely for the electron
rich nucleophile to approach electron rich arenes |
1 | 5650-5653 | Since it is difficult to
break a shorter bond than a longer bond, therefore, haloarenes
are less reactive than haloalkanes towards nucleophilic
substitution reaction (iii) Instability of phenyl cation: In case of haloarenes, the phenyl
cation formed as a result of self-ionisation will not be stabilised
by resonance and therefore, SN1 mechanism is ruled out (iv) Because of the possible repulsion, it is less likely for the electron
rich nucleophile to approach electron rich arenes Replacement by hydroxyl group
Chlorobenzene can be converted into phenol by heating in aqueous
sodium hydroxide solution at a temperature of 623K and a pressure
of 300 atmospheres |
1 | 5651-5654 | (iii) Instability of phenyl cation: In case of haloarenes, the phenyl
cation formed as a result of self-ionisation will not be stabilised
by resonance and therefore, SN1 mechanism is ruled out (iv) Because of the possible repulsion, it is less likely for the electron
rich nucleophile to approach electron rich arenes Replacement by hydroxyl group
Chlorobenzene can be converted into phenol by heating in aqueous
sodium hydroxide solution at a temperature of 623K and a pressure
of 300 atmospheres The presence of an electron withdrawing group (-NO2) at ortho- and
para-positions increases the reactivity of haloarenes |
1 | 5652-5655 | (iv) Because of the possible repulsion, it is less likely for the electron
rich nucleophile to approach electron rich arenes Replacement by hydroxyl group
Chlorobenzene can be converted into phenol by heating in aqueous
sodium hydroxide solution at a temperature of 623K and a pressure
of 300 atmospheres The presence of an electron withdrawing group (-NO2) at ortho- and
para-positions increases the reactivity of haloarenes Rationalised 2023-24
183 Haloalkanes and Haloarenes
The effect is pronounced when (-NO2) group is introduced at ortho-
and para- positions |
1 | 5653-5656 | Replacement by hydroxyl group
Chlorobenzene can be converted into phenol by heating in aqueous
sodium hydroxide solution at a temperature of 623K and a pressure
of 300 atmospheres The presence of an electron withdrawing group (-NO2) at ortho- and
para-positions increases the reactivity of haloarenes Rationalised 2023-24
183 Haloalkanes and Haloarenes
The effect is pronounced when (-NO2) group is introduced at ortho-
and para- positions However, no effect on reactivity of haloarenes is
observed by the presence of electron withdrawing group at meta-position |
1 | 5654-5657 | The presence of an electron withdrawing group (-NO2) at ortho- and
para-positions increases the reactivity of haloarenes Rationalised 2023-24
183 Haloalkanes and Haloarenes
The effect is pronounced when (-NO2) group is introduced at ortho-
and para- positions However, no effect on reactivity of haloarenes is
observed by the presence of electron withdrawing group at meta-position Mechanism of the reaction is as depicted:
Can you think why does NO2 group show its effect only at ortho- and para- positions
and not at meta- position |
1 | 5655-5658 | Rationalised 2023-24
183 Haloalkanes and Haloarenes
The effect is pronounced when (-NO2) group is introduced at ortho-
and para- positions However, no effect on reactivity of haloarenes is
observed by the presence of electron withdrawing group at meta-position Mechanism of the reaction is as depicted:
Can you think why does NO2 group show its effect only at ortho- and para- positions
and not at meta- position As shown, the presence of nitro group at ortho- and para-positions withdraws the
electron density from the benzene ring and thus facilitates the attack of the nucleophile
on haloarene |
1 | 5656-5659 | However, no effect on reactivity of haloarenes is
observed by the presence of electron withdrawing group at meta-position Mechanism of the reaction is as depicted:
Can you think why does NO2 group show its effect only at ortho- and para- positions
and not at meta- position As shown, the presence of nitro group at ortho- and para-positions withdraws the
electron density from the benzene ring and thus facilitates the attack of the nucleophile
on haloarene The carbanion thus formed is stabilised through resonance |
1 | 5657-5660 | Mechanism of the reaction is as depicted:
Can you think why does NO2 group show its effect only at ortho- and para- positions
and not at meta- position As shown, the presence of nitro group at ortho- and para-positions withdraws the
electron density from the benzene ring and thus facilitates the attack of the nucleophile
on haloarene The carbanion thus formed is stabilised through resonance The negative
charge appeared at ortho- and para- positions with respect to the halogen substituent is
stabilised by –NO2 group while in case of meta-nitrobenzene, none of the resonating
structures bear the negative charge on carbon atom bearing the –NO2 group |
1 | 5658-5661 | As shown, the presence of nitro group at ortho- and para-positions withdraws the
electron density from the benzene ring and thus facilitates the attack of the nucleophile
on haloarene The carbanion thus formed is stabilised through resonance The negative
charge appeared at ortho- and para- positions with respect to the halogen substituent is
stabilised by –NO2 group while in case of meta-nitrobenzene, none of the resonating
structures bear the negative charge on carbon atom bearing the –NO2 group Therefore,
the presence of nitro group at meta- position does not stabilise the negative charge and
no effect on reactivity is observed by the presence of –NO2 group at meta-position |
1 | 5659-5662 | The carbanion thus formed is stabilised through resonance The negative
charge appeared at ortho- and para- positions with respect to the halogen substituent is
stabilised by –NO2 group while in case of meta-nitrobenzene, none of the resonating
structures bear the negative charge on carbon atom bearing the –NO2 group Therefore,
the presence of nitro group at meta- position does not stabilise the negative charge and
no effect on reactivity is observed by the presence of –NO2 group at meta-position Rationalised 2023-24
184
Chemistry
2 |
1 | 5660-5663 | The negative
charge appeared at ortho- and para- positions with respect to the halogen substituent is
stabilised by –NO2 group while in case of meta-nitrobenzene, none of the resonating
structures bear the negative charge on carbon atom bearing the –NO2 group Therefore,
the presence of nitro group at meta- position does not stabilise the negative charge and
no effect on reactivity is observed by the presence of –NO2 group at meta-position Rationalised 2023-24
184
Chemistry
2 Electrophilic substitution reactions
Haloarenes undergo the usual electrophilic reactions of the benzene
ring such as halogenation, nitration, sulphonation and Friedel-Crafts
reactions |
1 | 5661-5664 | Therefore,
the presence of nitro group at meta- position does not stabilise the negative charge and
no effect on reactivity is observed by the presence of –NO2 group at meta-position Rationalised 2023-24
184
Chemistry
2 Electrophilic substitution reactions
Haloarenes undergo the usual electrophilic reactions of the benzene
ring such as halogenation, nitration, sulphonation and Friedel-Crafts
reactions Halogen atom besides being slightly deactivating is o, p-
directing; therefore, further substitution occurs at ortho- and para-
positions with respect to the halogen atom |
1 | 5662-5665 | Rationalised 2023-24
184
Chemistry
2 Electrophilic substitution reactions
Haloarenes undergo the usual electrophilic reactions of the benzene
ring such as halogenation, nitration, sulphonation and Friedel-Crafts
reactions Halogen atom besides being slightly deactivating is o, p-
directing; therefore, further substitution occurs at ortho- and para-
positions with respect to the halogen atom The o, p-directing influence
of halogen atom can be easily understood if we consider the resonating
structures of halobenzene as shown:
Due to resonance, the electron density increases more at ortho- and
para-positions than at meta-positions |
1 | 5663-5666 | Electrophilic substitution reactions
Haloarenes undergo the usual electrophilic reactions of the benzene
ring such as halogenation, nitration, sulphonation and Friedel-Crafts
reactions Halogen atom besides being slightly deactivating is o, p-
directing; therefore, further substitution occurs at ortho- and para-
positions with respect to the halogen atom The o, p-directing influence
of halogen atom can be easily understood if we consider the resonating
structures of halobenzene as shown:
Due to resonance, the electron density increases more at ortho- and
para-positions than at meta-positions Further, the halogen atom
because of its –I effect has some tendency to withdraw electrons from
the benzene ring |
1 | 5664-5667 | Halogen atom besides being slightly deactivating is o, p-
directing; therefore, further substitution occurs at ortho- and para-
positions with respect to the halogen atom The o, p-directing influence
of halogen atom can be easily understood if we consider the resonating
structures of halobenzene as shown:
Due to resonance, the electron density increases more at ortho- and
para-positions than at meta-positions Further, the halogen atom
because of its –I effect has some tendency to withdraw electrons from
the benzene ring As a result, the ring gets somewhat deactivated as
compared to benzene and hence the electrophilic substitution reactions
in haloarenes occur slowly and require more drastic conditions as
compared to those in benzene |
1 | 5665-5668 | The o, p-directing influence
of halogen atom can be easily understood if we consider the resonating
structures of halobenzene as shown:
Due to resonance, the electron density increases more at ortho- and
para-positions than at meta-positions Further, the halogen atom
because of its –I effect has some tendency to withdraw electrons from
the benzene ring As a result, the ring gets somewhat deactivated as
compared to benzene and hence the electrophilic substitution reactions
in haloarenes occur slowly and require more drastic conditions as
compared to those in benzene (i) Halogenation
(ii) Nitration
(iii) Sulphonation
Rationalised 2023-24
185 Haloalkanes and Haloarenes
(iv) Friedel-Crafts reaction
Although chlorine is an electron withdrawing group, yet it is ortho-,
para- directing in electrophilic aromatic substitution reactions |
1 | 5666-5669 | Further, the halogen atom
because of its –I effect has some tendency to withdraw electrons from
the benzene ring As a result, the ring gets somewhat deactivated as
compared to benzene and hence the electrophilic substitution reactions
in haloarenes occur slowly and require more drastic conditions as
compared to those in benzene (i) Halogenation
(ii) Nitration
(iii) Sulphonation
Rationalised 2023-24
185 Haloalkanes and Haloarenes
(iv) Friedel-Crafts reaction
Although chlorine is an electron withdrawing group, yet it is ortho-,
para- directing in electrophilic aromatic substitution reactions Why |
1 | 5667-5670 | As a result, the ring gets somewhat deactivated as
compared to benzene and hence the electrophilic substitution reactions
in haloarenes occur slowly and require more drastic conditions as
compared to those in benzene (i) Halogenation
(ii) Nitration
(iii) Sulphonation
Rationalised 2023-24
185 Haloalkanes and Haloarenes
(iv) Friedel-Crafts reaction
Although chlorine is an electron withdrawing group, yet it is ortho-,
para- directing in electrophilic aromatic substitution reactions Why Chlorine withdraws electrons through inductive effect and releases
electrons through resonance |
1 | 5668-5671 | (i) Halogenation
(ii) Nitration
(iii) Sulphonation
Rationalised 2023-24
185 Haloalkanes and Haloarenes
(iv) Friedel-Crafts reaction
Although chlorine is an electron withdrawing group, yet it is ortho-,
para- directing in electrophilic aromatic substitution reactions Why Chlorine withdraws electrons through inductive effect and releases
electrons through resonance Through inductive effect, chlorine
destabilises the intermediate carbocation formed during the electrophilic
substitution |
1 | 5669-5672 | Why Chlorine withdraws electrons through inductive effect and releases
electrons through resonance Through inductive effect, chlorine
destabilises the intermediate carbocation formed during the electrophilic
substitution Through resonance, halogen tends to stabilise the carbocation and
the effect is more pronounced at ortho- and para- positions |
1 | 5670-5673 | Chlorine withdraws electrons through inductive effect and releases
electrons through resonance Through inductive effect, chlorine
destabilises the intermediate carbocation formed during the electrophilic
substitution Through resonance, halogen tends to stabilise the carbocation and
the effect is more pronounced at ortho- and para- positions The
inductive effect is stronger than resonance and causes net electron
withdrawal and thus causes net deactivation |
1 | 5671-5674 | Through inductive effect, chlorine
destabilises the intermediate carbocation formed during the electrophilic
substitution Through resonance, halogen tends to stabilise the carbocation and
the effect is more pronounced at ortho- and para- positions The
inductive effect is stronger than resonance and causes net electron
withdrawal and thus causes net deactivation The resonance effect
tends to oppose the inductive effect for the attack at ortho- and para-
positions and hence makes the deactivation less for ortho- and para-
attack |
1 | 5672-5675 | Through resonance, halogen tends to stabilise the carbocation and
the effect is more pronounced at ortho- and para- positions The
inductive effect is stronger than resonance and causes net electron
withdrawal and thus causes net deactivation The resonance effect
tends to oppose the inductive effect for the attack at ortho- and para-
positions and hence makes the deactivation less for ortho- and para-
attack Reactivity is thus controlled by the stronger inductive effect
and orientation is controlled by resonance effect |
1 | 5673-5676 | The
inductive effect is stronger than resonance and causes net electron
withdrawal and thus causes net deactivation The resonance effect
tends to oppose the inductive effect for the attack at ortho- and para-
positions and hence makes the deactivation less for ortho- and para-
attack Reactivity is thus controlled by the stronger inductive effect
and orientation is controlled by resonance effect Example 6 |
1 | 5674-5677 | The resonance effect
tends to oppose the inductive effect for the attack at ortho- and para-
positions and hence makes the deactivation less for ortho- and para-
attack Reactivity is thus controlled by the stronger inductive effect
and orientation is controlled by resonance effect Example 6 9
Example 6 |
1 | 5675-5678 | Reactivity is thus controlled by the stronger inductive effect
and orientation is controlled by resonance effect Example 6 9
Example 6 9
Example 6 |
1 | 5676-5679 | Example 6 9
Example 6 9
Example 6 9
Example 6 |
1 | 5677-5680 | 9
Example 6 9
Example 6 9
Example 6 9
Example 6 |
1 | 5678-5681 | 9
Example 6 9
Example 6 9
Example 6 9
Solution
Solution
Solution
Solution
Solution
Rationalised 2023-24
186
Chemistry
Intext Questions
Intext Questions
Intext Questions
Intext Questions
Intext Questions
3 |
1 | 5679-5682 | 9
Example 6 9
Example 6 9
Solution
Solution
Solution
Solution
Solution
Rationalised 2023-24
186
Chemistry
Intext Questions
Intext Questions
Intext Questions
Intext Questions
Intext Questions
3 Reaction with metals
Wurtz-Fittig reaction
A mixture of an alkyl halide and aryl halide gives an alkylarene when
treated with sodium in dry ether and is called Wurtz-Fittig reaction |
1 | 5680-5683 | 9
Example 6 9
Solution
Solution
Solution
Solution
Solution
Rationalised 2023-24
186
Chemistry
Intext Questions
Intext Questions
Intext Questions
Intext Questions
Intext Questions
3 Reaction with metals
Wurtz-Fittig reaction
A mixture of an alkyl halide and aryl halide gives an alkylarene when
treated with sodium in dry ether and is called Wurtz-Fittig reaction Fittig reaction
Aryl halides also give analogous compounds when treated with sodium
in dry ether, in which two aryl groups are joined together |
1 | 5681-5684 | 9
Solution
Solution
Solution
Solution
Solution
Rationalised 2023-24
186
Chemistry
Intext Questions
Intext Questions
Intext Questions
Intext Questions
Intext Questions
3 Reaction with metals
Wurtz-Fittig reaction
A mixture of an alkyl halide and aryl halide gives an alkylarene when
treated with sodium in dry ether and is called Wurtz-Fittig reaction Fittig reaction
Aryl halides also give analogous compounds when treated with sodium
in dry ether, in which two aryl groups are joined together It is called
Fittig reaction |
1 | 5682-5685 | Reaction with metals
Wurtz-Fittig reaction
A mixture of an alkyl halide and aryl halide gives an alkylarene when
treated with sodium in dry ether and is called Wurtz-Fittig reaction Fittig reaction
Aryl halides also give analogous compounds when treated with sodium
in dry ether, in which two aryl groups are joined together It is called
Fittig reaction 6 |
1 | 5683-5686 | Fittig reaction
Aryl halides also give analogous compounds when treated with sodium
in dry ether, in which two aryl groups are joined together It is called
Fittig reaction 6 7
Which alkyl halide from the following pairs would you expect to react more
rapidly by an SN2 mechanism |
1 | 5684-5687 | It is called
Fittig reaction 6 7
Which alkyl halide from the following pairs would you expect to react more
rapidly by an SN2 mechanism Explain your answer |
1 | 5685-5688 | 6 7
Which alkyl halide from the following pairs would you expect to react more
rapidly by an SN2 mechanism Explain your answer 6 |
1 | 5686-5689 | 7
Which alkyl halide from the following pairs would you expect to react more
rapidly by an SN2 mechanism Explain your answer 6 8
In the following pairs of halogen compounds, which compound undergoes faster
SN1 reaction |
1 | 5687-5690 | Explain your answer 6 8
In the following pairs of halogen compounds, which compound undergoes faster
SN1 reaction 6 |
1 | 5688-5691 | 6 8
In the following pairs of halogen compounds, which compound undergoes faster
SN1 reaction 6 9
Identify A, B, C, D, E, R and R
1 in the following:
Rationalised 2023-24
187 Haloalkanes and Haloarenes
Carbon compounds containing more than one halogen atom are usually
referred to as polyhalogen compounds |
1 | 5689-5692 | 8
In the following pairs of halogen compounds, which compound undergoes faster
SN1 reaction 6 9
Identify A, B, C, D, E, R and R
1 in the following:
Rationalised 2023-24
187 Haloalkanes and Haloarenes
Carbon compounds containing more than one halogen atom are usually
referred to as polyhalogen compounds Many of these compounds are
useful in industry and agriculture |
1 | 5690-5693 | 6 9
Identify A, B, C, D, E, R and R
1 in the following:
Rationalised 2023-24
187 Haloalkanes and Haloarenes
Carbon compounds containing more than one halogen atom are usually
referred to as polyhalogen compounds Many of these compounds are
useful in industry and agriculture Some polyhalogen compounds are
described in this section |
1 | 5691-5694 | 9
Identify A, B, C, D, E, R and R
1 in the following:
Rationalised 2023-24
187 Haloalkanes and Haloarenes
Carbon compounds containing more than one halogen atom are usually
referred to as polyhalogen compounds Many of these compounds are
useful in industry and agriculture Some polyhalogen compounds are
described in this section Dichloromethane is widely used as a solvent as a paint remover, as a
propellant in aerosols, and as a process solvent in the manufacture of
drugs |
1 | 5692-5695 | Many of these compounds are
useful in industry and agriculture Some polyhalogen compounds are
described in this section Dichloromethane is widely used as a solvent as a paint remover, as a
propellant in aerosols, and as a process solvent in the manufacture of
drugs It is also used as a metal cleaning and finishing solvent |
1 | 5693-5696 | Some polyhalogen compounds are
described in this section Dichloromethane is widely used as a solvent as a paint remover, as a
propellant in aerosols, and as a process solvent in the manufacture of
drugs It is also used as a metal cleaning and finishing solvent Methylene
chloride harms the human central nervous system |
1 | 5694-5697 | Dichloromethane is widely used as a solvent as a paint remover, as a
propellant in aerosols, and as a process solvent in the manufacture of
drugs It is also used as a metal cleaning and finishing solvent Methylene
chloride harms the human central nervous system Exposure to lower
levels of methylene chloride in air can lead to slightly impaired hearing
and vision |
1 | 5695-5698 | It is also used as a metal cleaning and finishing solvent Methylene
chloride harms the human central nervous system Exposure to lower
levels of methylene chloride in air can lead to slightly impaired hearing
and vision Higher levels of methylene chloride in air cause dizziness,
nausea, tingling and numbness in the fingers and toes |
1 | 5696-5699 | Methylene
chloride harms the human central nervous system Exposure to lower
levels of methylene chloride in air can lead to slightly impaired hearing
and vision Higher levels of methylene chloride in air cause dizziness,
nausea, tingling and numbness in the fingers and toes In humans, direct
skin contact with methylene chloride causes intense burning and mild
redness of the skin |
1 | 5697-5700 | Exposure to lower
levels of methylene chloride in air can lead to slightly impaired hearing
and vision Higher levels of methylene chloride in air cause dizziness,
nausea, tingling and numbness in the fingers and toes In humans, direct
skin contact with methylene chloride causes intense burning and mild
redness of the skin Direct contact with the eyes can burn the cornea |
1 | 5698-5701 | Higher levels of methylene chloride in air cause dizziness,
nausea, tingling and numbness in the fingers and toes In humans, direct
skin contact with methylene chloride causes intense burning and mild
redness of the skin Direct contact with the eyes can burn the cornea Chemically, chloroform is employed as a solvent for fats, alkaloids,
iodine and other substances |
1 | 5699-5702 | In humans, direct
skin contact with methylene chloride causes intense burning and mild
redness of the skin Direct contact with the eyes can burn the cornea Chemically, chloroform is employed as a solvent for fats, alkaloids,
iodine and other substances The major use of chloroform today is in
the production of the freon refrigerant R-22 |
1 | 5700-5703 | Direct contact with the eyes can burn the cornea Chemically, chloroform is employed as a solvent for fats, alkaloids,
iodine and other substances The major use of chloroform today is in
the production of the freon refrigerant R-22 It was once used as a
general anaesthetic in surgery but has been replaced by less toxic,
safer anaesthetics, such as ether |
1 | 5701-5704 | Chemically, chloroform is employed as a solvent for fats, alkaloids,
iodine and other substances The major use of chloroform today is in
the production of the freon refrigerant R-22 It was once used as a
general anaesthetic in surgery but has been replaced by less toxic,
safer anaesthetics, such as ether As might be expected from its use as
an anaesthetic, inhaling chloroform vapours depresses the central
nervous system |
1 | 5702-5705 | The major use of chloroform today is in
the production of the freon refrigerant R-22 It was once used as a
general anaesthetic in surgery but has been replaced by less toxic,
safer anaesthetics, such as ether As might be expected from its use as
an anaesthetic, inhaling chloroform vapours depresses the central
nervous system Breathing about 900 parts of chloroform per million
parts of air (900 parts per million) for a short time can cause dizziness,
fatigue, and headache |
1 | 5703-5706 | It was once used as a
general anaesthetic in surgery but has been replaced by less toxic,
safer anaesthetics, such as ether As might be expected from its use as
an anaesthetic, inhaling chloroform vapours depresses the central
nervous system Breathing about 900 parts of chloroform per million
parts of air (900 parts per million) for a short time can cause dizziness,
fatigue, and headache Chronic chloroform exposure may cause damage
to the liver (where chloroform is metabolised to phosgene) and to the
kidneys, and some people develop sores when the skin is immersed in
chloroform |
1 | 5704-5707 | As might be expected from its use as
an anaesthetic, inhaling chloroform vapours depresses the central
nervous system Breathing about 900 parts of chloroform per million
parts of air (900 parts per million) for a short time can cause dizziness,
fatigue, and headache Chronic chloroform exposure may cause damage
to the liver (where chloroform is metabolised to phosgene) and to the
kidneys, and some people develop sores when the skin is immersed in
chloroform Chloroform is slowly oxidised by air in the presence of
light to an extremely poisonous gas, carbonyl chloride, also known as
phosgene |
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