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1 | 5505-5508 | 7
Example 6 7
Example 6 7
Predict the order of reactivity of the following
compounds in SN1 and SN2 reactions:
(i) The four isomeric bromobutanes
(ii) C6H5CH2Br, C6H5CH(C6H5)Br, C6H5CH(CH3)Br, C6H5C(CH3)(C6H5)Br
For a given alkyl group, the reactivity of the halide, R-X, follows the same order in both the
mechanisms R–I> R–Br>R–Cl>>R–F Rationalised 2023-24
175 Haloalkanes and Haloarenes
(c) Stereochemical aspects of nucleophilic substitution reactions
In order to understand the stereochemical aspects of substitution
reactions, we need to learn some basic stereochemical principles
and notations (optical activity, chirality, retention, inversion,
racemisation, etc |
1 | 5506-5509 | 7
Example 6 7
Predict the order of reactivity of the following
compounds in SN1 and SN2 reactions:
(i) The four isomeric bromobutanes
(ii) C6H5CH2Br, C6H5CH(C6H5)Br, C6H5CH(CH3)Br, C6H5C(CH3)(C6H5)Br
For a given alkyl group, the reactivity of the halide, R-X, follows the same order in both the
mechanisms R–I> R–Br>R–Cl>>R–F Rationalised 2023-24
175 Haloalkanes and Haloarenes
(c) Stereochemical aspects of nucleophilic substitution reactions
In order to understand the stereochemical aspects of substitution
reactions, we need to learn some basic stereochemical principles
and notations (optical activity, chirality, retention, inversion,
racemisation, etc ) |
1 | 5507-5510 | 7
Predict the order of reactivity of the following
compounds in SN1 and SN2 reactions:
(i) The four isomeric bromobutanes
(ii) C6H5CH2Br, C6H5CH(C6H5)Br, C6H5CH(CH3)Br, C6H5C(CH3)(C6H5)Br
For a given alkyl group, the reactivity of the halide, R-X, follows the same order in both the
mechanisms R–I> R–Br>R–Cl>>R–F Rationalised 2023-24
175 Haloalkanes and Haloarenes
(c) Stereochemical aspects of nucleophilic substitution reactions
In order to understand the stereochemical aspects of substitution
reactions, we need to learn some basic stereochemical principles
and notations (optical activity, chirality, retention, inversion,
racemisation, etc ) (i) Optical activity: Plane of plane polarised light produced by
passing ordinary light through Nicol prism is rotated when it
is passed through the solutions of certain compounds |
1 | 5508-5511 | Rationalised 2023-24
175 Haloalkanes and Haloarenes
(c) Stereochemical aspects of nucleophilic substitution reactions
In order to understand the stereochemical aspects of substitution
reactions, we need to learn some basic stereochemical principles
and notations (optical activity, chirality, retention, inversion,
racemisation, etc ) (i) Optical activity: Plane of plane polarised light produced by
passing ordinary light through Nicol prism is rotated when it
is passed through the solutions of certain compounds Such
compounds are called optically active compounds |
1 | 5509-5512 | ) (i) Optical activity: Plane of plane polarised light produced by
passing ordinary light through Nicol prism is rotated when it
is passed through the solutions of certain compounds Such
compounds are called optically active compounds The angle
by which the plane polarised light is rotated is measured by an
instrument called polarimeter |
1 | 5510-5513 | (i) Optical activity: Plane of plane polarised light produced by
passing ordinary light through Nicol prism is rotated when it
is passed through the solutions of certain compounds Such
compounds are called optically active compounds The angle
by which the plane polarised light is rotated is measured by an
instrument called polarimeter If the compound rotates the plane
of plane polarised light to the right, i |
1 | 5511-5514 | Such
compounds are called optically active compounds The angle
by which the plane polarised light is rotated is measured by an
instrument called polarimeter If the compound rotates the plane
of plane polarised light to the right, i e |
1 | 5512-5515 | The angle
by which the plane polarised light is rotated is measured by an
instrument called polarimeter If the compound rotates the plane
of plane polarised light to the right, i e , clockwise direction, it
is called dextrorotatory (Greek for right rotating) or the d-form
and is indicated by placing a positive (+) sign before the degree
of rotation |
1 | 5513-5516 | If the compound rotates the plane
of plane polarised light to the right, i e , clockwise direction, it
is called dextrorotatory (Greek for right rotating) or the d-form
and is indicated by placing a positive (+) sign before the degree
of rotation If the light is rotated towards left (anticlockwise
direction), the compound is said to be laevo-rotatory or the
l-form and a negative (–) sign is placed before the degree of
rotation |
1 | 5514-5517 | e , clockwise direction, it
is called dextrorotatory (Greek for right rotating) or the d-form
and is indicated by placing a positive (+) sign before the degree
of rotation If the light is rotated towards left (anticlockwise
direction), the compound is said to be laevo-rotatory or the
l-form and a negative (–) sign is placed before the degree of
rotation Such (+) and (–) isomers of a compound are called
optical isomers and the phenomenon is termed as optical
isomerism |
1 | 5515-5518 | , clockwise direction, it
is called dextrorotatory (Greek for right rotating) or the d-form
and is indicated by placing a positive (+) sign before the degree
of rotation If the light is rotated towards left (anticlockwise
direction), the compound is said to be laevo-rotatory or the
l-form and a negative (–) sign is placed before the degree of
rotation Such (+) and (–) isomers of a compound are called
optical isomers and the phenomenon is termed as optical
isomerism (ii) Molecular asymmetry, chirality and enantiomers: The
observation of Louis Pasteur (1848) that crystals of certain
compounds exist in the form of mirror images laid the
foundation of modern stereochemistry |
1 | 5516-5519 | If the light is rotated towards left (anticlockwise
direction), the compound is said to be laevo-rotatory or the
l-form and a negative (–) sign is placed before the degree of
rotation Such (+) and (–) isomers of a compound are called
optical isomers and the phenomenon is termed as optical
isomerism (ii) Molecular asymmetry, chirality and enantiomers: The
observation of Louis Pasteur (1848) that crystals of certain
compounds exist in the form of mirror images laid the
foundation of modern stereochemistry He demonstrated that
aqueous solutions of both types of crystals showed optical
rotation, equal in magnitude (for solution of equal concentration)
but opposite in direction |
1 | 5517-5520 | Such (+) and (–) isomers of a compound are called
optical isomers and the phenomenon is termed as optical
isomerism (ii) Molecular asymmetry, chirality and enantiomers: The
observation of Louis Pasteur (1848) that crystals of certain
compounds exist in the form of mirror images laid the
foundation of modern stereochemistry He demonstrated that
aqueous solutions of both types of crystals showed optical
rotation, equal in magnitude (for solution of equal concentration)
but opposite in direction He believed that this difference in
optical activity was associated with the three dimensional
arrangements of atoms in the molecules (configurations) of
(i) CH3CH2CH2CH2Br < (CH3)2CHCH2Br < CH3CH2CH(Br)CH3 < (CH3)3CBr (SN1)
CH3CH2CH2CH2Br > (CH3)2CHCH2Br > CH3CH2CH(Br)CH3> (CH3)3CBr (SN2)
Of the two primary bromides, the carbocation intermediate derived from
(CH3)2CHCH2Br is more stable than derived from CH3CH2CH2CH2Br because
of greater electron donating inductive effect of (CH3)2CH- group |
1 | 5518-5521 | (ii) Molecular asymmetry, chirality and enantiomers: The
observation of Louis Pasteur (1848) that crystals of certain
compounds exist in the form of mirror images laid the
foundation of modern stereochemistry He demonstrated that
aqueous solutions of both types of crystals showed optical
rotation, equal in magnitude (for solution of equal concentration)
but opposite in direction He believed that this difference in
optical activity was associated with the three dimensional
arrangements of atoms in the molecules (configurations) of
(i) CH3CH2CH2CH2Br < (CH3)2CHCH2Br < CH3CH2CH(Br)CH3 < (CH3)3CBr (SN1)
CH3CH2CH2CH2Br > (CH3)2CHCH2Br > CH3CH2CH(Br)CH3> (CH3)3CBr (SN2)
Of the two primary bromides, the carbocation intermediate derived from
(CH3)2CHCH2Br is more stable than derived from CH3CH2CH2CH2Br because
of greater electron donating inductive effect of (CH3)2CH- group Therefore,
(CH3)2CHCH2Br is more reactive than CH3CH2CH2CH2Br in SN1 reactions |
1 | 5519-5522 | He demonstrated that
aqueous solutions of both types of crystals showed optical
rotation, equal in magnitude (for solution of equal concentration)
but opposite in direction He believed that this difference in
optical activity was associated with the three dimensional
arrangements of atoms in the molecules (configurations) of
(i) CH3CH2CH2CH2Br < (CH3)2CHCH2Br < CH3CH2CH(Br)CH3 < (CH3)3CBr (SN1)
CH3CH2CH2CH2Br > (CH3)2CHCH2Br > CH3CH2CH(Br)CH3> (CH3)3CBr (SN2)
Of the two primary bromides, the carbocation intermediate derived from
(CH3)2CHCH2Br is more stable than derived from CH3CH2CH2CH2Br because
of greater electron donating inductive effect of (CH3)2CH- group Therefore,
(CH3)2CHCH2Br is more reactive than CH3CH2CH2CH2Br in SN1 reactions CH3CH2CH(Br)CH3 is a secondary bromide and (CH3)3CBr is a tertiary
bromide |
1 | 5520-5523 | He believed that this difference in
optical activity was associated with the three dimensional
arrangements of atoms in the molecules (configurations) of
(i) CH3CH2CH2CH2Br < (CH3)2CHCH2Br < CH3CH2CH(Br)CH3 < (CH3)3CBr (SN1)
CH3CH2CH2CH2Br > (CH3)2CHCH2Br > CH3CH2CH(Br)CH3> (CH3)3CBr (SN2)
Of the two primary bromides, the carbocation intermediate derived from
(CH3)2CHCH2Br is more stable than derived from CH3CH2CH2CH2Br because
of greater electron donating inductive effect of (CH3)2CH- group Therefore,
(CH3)2CHCH2Br is more reactive than CH3CH2CH2CH2Br in SN1 reactions CH3CH2CH(Br)CH3 is a secondary bromide and (CH3)3CBr is a tertiary
bromide Hence the above order is followed in SN1 |
1 | 5521-5524 | Therefore,
(CH3)2CHCH2Br is more reactive than CH3CH2CH2CH2Br in SN1 reactions CH3CH2CH(Br)CH3 is a secondary bromide and (CH3)3CBr is a tertiary
bromide Hence the above order is followed in SN1 The reactivity in SN2
reactions follows the reverse order as the steric hinderance around the
electrophilic carbon increases in that order |
1 | 5522-5525 | CH3CH2CH(Br)CH3 is a secondary bromide and (CH3)3CBr is a tertiary
bromide Hence the above order is followed in SN1 The reactivity in SN2
reactions follows the reverse order as the steric hinderance around the
electrophilic carbon increases in that order (ii) C6H5C(CH3)(C6H5)Br > C6H5CH(C6H5)Br > C6H5CH(CH3)Br > C6H5CH2Br (SN1)
C6H5C(CH3)(C6H5)Br < C6H5CH(C6H5)Br < C6H5CH(CH3)Br < C6H5CH2Br (SN2)
Of the two secondary bromides, the carbocation intermediate obtained
from C6H5CH(C6H5)Br is more stable than obtained from C6H5CH(CH3)Br
because it is stabilised by two phenyl groups due to resonance |
1 | 5523-5526 | Hence the above order is followed in SN1 The reactivity in SN2
reactions follows the reverse order as the steric hinderance around the
electrophilic carbon increases in that order (ii) C6H5C(CH3)(C6H5)Br > C6H5CH(C6H5)Br > C6H5CH(CH3)Br > C6H5CH2Br (SN1)
C6H5C(CH3)(C6H5)Br < C6H5CH(C6H5)Br < C6H5CH(CH3)Br < C6H5CH2Br (SN2)
Of the two secondary bromides, the carbocation intermediate obtained
from C6H5CH(C6H5)Br is more stable than obtained from C6H5CH(CH3)Br
because it is stabilised by two phenyl groups due to resonance Therefore,
the former bromide is more reactive than the latter in SN1 reactions |
1 | 5524-5527 | The reactivity in SN2
reactions follows the reverse order as the steric hinderance around the
electrophilic carbon increases in that order (ii) C6H5C(CH3)(C6H5)Br > C6H5CH(C6H5)Br > C6H5CH(CH3)Br > C6H5CH2Br (SN1)
C6H5C(CH3)(C6H5)Br < C6H5CH(C6H5)Br < C6H5CH(CH3)Br < C6H5CH2Br (SN2)
Of the two secondary bromides, the carbocation intermediate obtained
from C6H5CH(C6H5)Br is more stable than obtained from C6H5CH(CH3)Br
because it is stabilised by two phenyl groups due to resonance Therefore,
the former bromide is more reactive than the latter in SN1 reactions A
phenyl group is bulkier than a methyl group |
1 | 5525-5528 | (ii) C6H5C(CH3)(C6H5)Br > C6H5CH(C6H5)Br > C6H5CH(CH3)Br > C6H5CH2Br (SN1)
C6H5C(CH3)(C6H5)Br < C6H5CH(C6H5)Br < C6H5CH(CH3)Br < C6H5CH2Br (SN2)
Of the two secondary bromides, the carbocation intermediate obtained
from C6H5CH(C6H5)Br is more stable than obtained from C6H5CH(CH3)Br
because it is stabilised by two phenyl groups due to resonance Therefore,
the former bromide is more reactive than the latter in SN1 reactions A
phenyl group is bulkier than a methyl group Therefore, C6H5CH(C6H5)Br
is less reactive than C6H5CH(CH3)Br in SN2 reactions |
1 | 5526-5529 | Therefore,
the former bromide is more reactive than the latter in SN1 reactions A
phenyl group is bulkier than a methyl group Therefore, C6H5CH(C6H5)Br
is less reactive than C6H5CH(CH3)Br in SN2 reactions Solution
Solution
Solution
Solution
Solution
William Nicol (1768-
1851) developed the first
prism that produced
plane polarised light |
1 | 5527-5530 | A
phenyl group is bulkier than a methyl group Therefore, C6H5CH(C6H5)Br
is less reactive than C6H5CH(CH3)Br in SN2 reactions Solution
Solution
Solution
Solution
Solution
William Nicol (1768-
1851) developed the first
prism that produced
plane polarised light Rationalised 2023-24
176
Chemistry
two types of crystals |
1 | 5528-5531 | Therefore, C6H5CH(C6H5)Br
is less reactive than C6H5CH(CH3)Br in SN2 reactions Solution
Solution
Solution
Solution
Solution
William Nicol (1768-
1851) developed the first
prism that produced
plane polarised light Rationalised 2023-24
176
Chemistry
two types of crystals Dutch scientist, J |
1 | 5529-5532 | Solution
Solution
Solution
Solution
Solution
William Nicol (1768-
1851) developed the first
prism that produced
plane polarised light Rationalised 2023-24
176
Chemistry
two types of crystals Dutch scientist, J Van’t Hoff and French
scientist, C |
1 | 5530-5533 | Rationalised 2023-24
176
Chemistry
two types of crystals Dutch scientist, J Van’t Hoff and French
scientist, C Le Bel in the same year (1874), independently
argued that the spatial arrangement of four groups (valencies)
around a central carbon is tetrahedral and if all the substituents
attached to that carbon are different, the mirror image of the
molecule is not superimposed (overlapped) on the molecule;
such a carbon is called asymmetric carbon or stereocentre |
1 | 5531-5534 | Dutch scientist, J Van’t Hoff and French
scientist, C Le Bel in the same year (1874), independently
argued that the spatial arrangement of four groups (valencies)
around a central carbon is tetrahedral and if all the substituents
attached to that carbon are different, the mirror image of the
molecule is not superimposed (overlapped) on the molecule;
such a carbon is called asymmetric carbon or stereocentre The resulting molecule would lack symmetry and is referred to
as asymmetric molecule |
1 | 5532-5535 | Van’t Hoff and French
scientist, C Le Bel in the same year (1874), independently
argued that the spatial arrangement of four groups (valencies)
around a central carbon is tetrahedral and if all the substituents
attached to that carbon are different, the mirror image of the
molecule is not superimposed (overlapped) on the molecule;
such a carbon is called asymmetric carbon or stereocentre The resulting molecule would lack symmetry and is referred to
as asymmetric molecule The asymmetry of the molecule along
with non superimposability of mirror images is responsible for
the optical activity in such organic compounds |
1 | 5533-5536 | Le Bel in the same year (1874), independently
argued that the spatial arrangement of four groups (valencies)
around a central carbon is tetrahedral and if all the substituents
attached to that carbon are different, the mirror image of the
molecule is not superimposed (overlapped) on the molecule;
such a carbon is called asymmetric carbon or stereocentre The resulting molecule would lack symmetry and is referred to
as asymmetric molecule The asymmetry of the molecule along
with non superimposability of mirror images is responsible for
the optical activity in such organic compounds The symmetry and asymmetry are also observed in many day to day
objects: a sphere, a cube, a cone, are all identical to
their mirror images and can be superimposed |
1 | 5534-5537 | The resulting molecule would lack symmetry and is referred to
as asymmetric molecule The asymmetry of the molecule along
with non superimposability of mirror images is responsible for
the optical activity in such organic compounds The symmetry and asymmetry are also observed in many day to day
objects: a sphere, a cube, a cone, are all identical to
their mirror images and can be superimposed However, many objects are non superimposable on
their mirror images |
1 | 5535-5538 | The asymmetry of the molecule along
with non superimposability of mirror images is responsible for
the optical activity in such organic compounds The symmetry and asymmetry are also observed in many day to day
objects: a sphere, a cube, a cone, are all identical to
their mirror images and can be superimposed However, many objects are non superimposable on
their mirror images For example, your left and right
hand look similar but if you put your left hand on
your right hand by moving them in the same plane,
they do not coincide |
1 | 5536-5539 | The symmetry and asymmetry are also observed in many day to day
objects: a sphere, a cube, a cone, are all identical to
their mirror images and can be superimposed However, many objects are non superimposable on
their mirror images For example, your left and right
hand look similar but if you put your left hand on
your right hand by moving them in the same plane,
they do not coincide The objects which are non-
superimposable on their mirror image (like a pair
of hands) are said to be chiral and this property is
known as chirality |
1 | 5537-5540 | However, many objects are non superimposable on
their mirror images For example, your left and right
hand look similar but if you put your left hand on
your right hand by moving them in the same plane,
they do not coincide The objects which are non-
superimposable on their mirror image (like a pair
of hands) are said to be chiral and this property is
known as chirality Chiral molecules are optically
active, while the objects, which are, superimposable
on their mirror images are called achiral |
1 | 5538-5541 | For example, your left and right
hand look similar but if you put your left hand on
your right hand by moving them in the same plane,
they do not coincide The objects which are non-
superimposable on their mirror image (like a pair
of hands) are said to be chiral and this property is
known as chirality Chiral molecules are optically
active, while the objects, which are, superimposable
on their mirror images are called achiral These
molecules are optically inactive |
1 | 5539-5542 | The objects which are non-
superimposable on their mirror image (like a pair
of hands) are said to be chiral and this property is
known as chirality Chiral molecules are optically
active, while the objects, which are, superimposable
on their mirror images are called achiral These
molecules are optically inactive The above test of molecular chirality can be
applied to organic molecules by constructing
models and its mirror images or by drawing three
dimensional structures and attempting to
superimpose them in our minds |
1 | 5540-5543 | Chiral molecules are optically
active, while the objects, which are, superimposable
on their mirror images are called achiral These
molecules are optically inactive The above test of molecular chirality can be
applied to organic molecules by constructing
models and its mirror images or by drawing three
dimensional structures and attempting to
superimpose them in our minds There are other
aids, however, that can assist us in recognising
chiral molecules |
1 | 5541-5544 | These
molecules are optically inactive The above test of molecular chirality can be
applied to organic molecules by constructing
models and its mirror images or by drawing three
dimensional structures and attempting to
superimpose them in our minds There are other
aids, however, that can assist us in recognising
chiral molecules One such aid is the presence of
As you can see very clearly, propan-2-ol (A) does not contain an asymmetric
carbon, as all the four groups attached to the tetrahedral carbon are not
different |
1 | 5542-5545 | The above test of molecular chirality can be
applied to organic molecules by constructing
models and its mirror images or by drawing three
dimensional structures and attempting to
superimpose them in our minds There are other
aids, however, that can assist us in recognising
chiral molecules One such aid is the presence of
As you can see very clearly, propan-2-ol (A) does not contain an asymmetric
carbon, as all the four groups attached to the tetrahedral carbon are not
different We rotate the mirror image (B) of the molecule by 180° (structure
C) and try to overlap the structure (C) with the structure (A), these structures
completely overlap |
1 | 5543-5546 | There are other
aids, however, that can assist us in recognising
chiral molecules One such aid is the presence of
As you can see very clearly, propan-2-ol (A) does not contain an asymmetric
carbon, as all the four groups attached to the tetrahedral carbon are not
different We rotate the mirror image (B) of the molecule by 180° (structure
C) and try to overlap the structure (C) with the structure (A), these structures
completely overlap Thus propan-2-ol is an achiral molecule |
1 | 5544-5547 | One such aid is the presence of
As you can see very clearly, propan-2-ol (A) does not contain an asymmetric
carbon, as all the four groups attached to the tetrahedral carbon are not
different We rotate the mirror image (B) of the molecule by 180° (structure
C) and try to overlap the structure (C) with the structure (A), these structures
completely overlap Thus propan-2-ol is an achiral molecule Jacobus
Hendricus
Van’t Hoff (1852-1911)
received the first Nobel
Prize in Chemistry in
1901 for his work on
solutions |
1 | 5545-5548 | We rotate the mirror image (B) of the molecule by 180° (structure
C) and try to overlap the structure (C) with the structure (A), these structures
completely overlap Thus propan-2-ol is an achiral molecule Jacobus
Hendricus
Van’t Hoff (1852-1911)
received the first Nobel
Prize in Chemistry in
1901 for his work on
solutions Fig 6 |
1 | 5546-5549 | Thus propan-2-ol is an achiral molecule Jacobus
Hendricus
Van’t Hoff (1852-1911)
received the first Nobel
Prize in Chemistry in
1901 for his work on
solutions Fig 6 4:
Some common examples of chiral and
achiral objects
a single asymmetric carbon atom |
1 | 5547-5550 | Jacobus
Hendricus
Van’t Hoff (1852-1911)
received the first Nobel
Prize in Chemistry in
1901 for his work on
solutions Fig 6 4:
Some common examples of chiral and
achiral objects
a single asymmetric carbon atom Let us consider
two simple molecules propan-2-ol (Fig |
1 | 5548-5551 | Fig 6 4:
Some common examples of chiral and
achiral objects
a single asymmetric carbon atom Let us consider
two simple molecules propan-2-ol (Fig 6 |
1 | 5549-5552 | 4:
Some common examples of chiral and
achiral objects
a single asymmetric carbon atom Let us consider
two simple molecules propan-2-ol (Fig 6 5) and butan-2-ol (Fig |
1 | 5550-5553 | Let us consider
two simple molecules propan-2-ol (Fig 6 5) and butan-2-ol (Fig 6 |
1 | 5551-5554 | 6 5) and butan-2-ol (Fig 6 6)
and their mirror images |
1 | 5552-5555 | 5) and butan-2-ol (Fig 6 6)
and their mirror images Fig 6 |
1 | 5553-5556 | 6 6)
and their mirror images Fig 6 5:
B is mirror image of A; B is rotated by 180o and C is
obtained; C is superimposable on A |
1 | 5554-5557 | 6)
and their mirror images Fig 6 5:
B is mirror image of A; B is rotated by 180o and C is
obtained; C is superimposable on A Rationalised 2023-24
177 Haloalkanes and Haloarenes
Butan-2-ol has four different groups attached to
the tetrahedral carbon and as expected is chiral |
1 | 5555-5558 | Fig 6 5:
B is mirror image of A; B is rotated by 180o and C is
obtained; C is superimposable on A Rationalised 2023-24
177 Haloalkanes and Haloarenes
Butan-2-ol has four different groups attached to
the tetrahedral carbon and as expected is chiral Some common
examples
of
chiral
molecules
such
as
2-chlorobutane, 2, 3-dihyroxypropanal, (OHC–CHOH–CH2OH),
bromochloro-iodomethane (BrClCHI), 2-bromopropanoic acid
(H3C–CHBr–COOH), etc |
1 | 5556-5559 | 5:
B is mirror image of A; B is rotated by 180o and C is
obtained; C is superimposable on A Rationalised 2023-24
177 Haloalkanes and Haloarenes
Butan-2-ol has four different groups attached to
the tetrahedral carbon and as expected is chiral Some common
examples
of
chiral
molecules
such
as
2-chlorobutane, 2, 3-dihyroxypropanal, (OHC–CHOH–CH2OH),
bromochloro-iodomethane (BrClCHI), 2-bromopropanoic acid
(H3C–CHBr–COOH), etc Fig |
1 | 5557-5560 | Rationalised 2023-24
177 Haloalkanes and Haloarenes
Butan-2-ol has four different groups attached to
the tetrahedral carbon and as expected is chiral Some common
examples
of
chiral
molecules
such
as
2-chlorobutane, 2, 3-dihyroxypropanal, (OHC–CHOH–CH2OH),
bromochloro-iodomethane (BrClCHI), 2-bromopropanoic acid
(H3C–CHBr–COOH), etc Fig 6 |
1 | 5558-5561 | Some common
examples
of
chiral
molecules
such
as
2-chlorobutane, 2, 3-dihyroxypropanal, (OHC–CHOH–CH2OH),
bromochloro-iodomethane (BrClCHI), 2-bromopropanoic acid
(H3C–CHBr–COOH), etc Fig 6 7:
A chiral molecule
and its mirror image
The stereoisomers related to each other as non-
superimposable mirror images are called enantiomers
(Fig |
1 | 5559-5562 | Fig 6 7:
A chiral molecule
and its mirror image
The stereoisomers related to each other as non-
superimposable mirror images are called enantiomers
(Fig 6 |
1 | 5560-5563 | 6 7:
A chiral molecule
and its mirror image
The stereoisomers related to each other as non-
superimposable mirror images are called enantiomers
(Fig 6 7) |
1 | 5561-5564 | 7:
A chiral molecule
and its mirror image
The stereoisomers related to each other as non-
superimposable mirror images are called enantiomers
(Fig 6 7) A and B in Fig |
1 | 5562-5565 | 6 7) A and B in Fig 6 |
1 | 5563-5566 | 7) A and B in Fig 6 5 and D and E in Fig |
1 | 5564-5567 | A and B in Fig 6 5 and D and E in Fig 6 |
1 | 5565-5568 | 6 5 and D and E in Fig 6 6 are
enantiomers |
1 | 5566-5569 | 5 and D and E in Fig 6 6 are
enantiomers Enantiomers possess identical physical properties namely,
melting point, boiling point, refractive index, etc |
1 | 5567-5570 | 6 6 are
enantiomers Enantiomers possess identical physical properties namely,
melting point, boiling point, refractive index, etc They only differ
with respect to the rotation of plane polarised light |
1 | 5568-5571 | 6 are
enantiomers Enantiomers possess identical physical properties namely,
melting point, boiling point, refractive index, etc They only differ
with respect to the rotation of plane polarised light If one of the
enantiomer is dextro rotatory, the other will be laevo rotatory |
1 | 5569-5572 | Enantiomers possess identical physical properties namely,
melting point, boiling point, refractive index, etc They only differ
with respect to the rotation of plane polarised light If one of the
enantiomer is dextro rotatory, the other will be laevo rotatory 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 |
1 | 5570-5573 | They only differ
with respect to the rotation of plane polarised light If one of the
enantiomer is dextro rotatory, the other will be laevo rotatory 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 known as racemic mixture or racemic
modification |
1 | 5571-5574 | If one of the
enantiomer is dextro rotatory, the other will be laevo rotatory 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 known as racemic mixture or racemic
modification A racemic mixture is represented by prefixing dl
or (±) before the name, for example (±) butan-2-ol |
1 | 5572-5575 | 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 known as racemic mixture or racemic
modification A racemic mixture is represented by prefixing dl
or (±) before the name, for example (±) butan-2-ol The process
of conversion of enantiomer into a racemic mixture is known as
racemisation |
1 | 5573-5576 | Such
a mixture is known as racemic mixture or racemic
modification A racemic mixture is represented by prefixing dl
or (±) before the name, for example (±) butan-2-ol The process
of conversion of enantiomer into a racemic mixture is known as
racemisation Example 6 |
1 | 5574-5577 | A racemic mixture is represented by prefixing dl
or (±) before the name, for example (±) butan-2-ol The process
of conversion of enantiomer into a racemic mixture is known as
racemisation Example 6 8
Example 6 |
1 | 5575-5578 | The process
of conversion of enantiomer into a racemic mixture is known as
racemisation Example 6 8
Example 6 8
Example 6 |
1 | 5576-5579 | Example 6 8
Example 6 8
Example 6 8
Example 6 |
1 | 5577-5580 | 8
Example 6 8
Example 6 8
Example 6 8
Example 6 |
1 | 5578-5581 | 8
Example 6 8
Example 6 8
Example 6 8
Identify chiral and achiral molecules in each of the following pair of
compounds |
1 | 5579-5582 | 8
Example 6 8
Example 6 8
Identify chiral and achiral molecules in each of the following pair of
compounds (Wedge and Dash representations according to Class XI |
1 | 5580-5583 | 8
Example 6 8
Identify chiral and achiral molecules in each of the following pair of
compounds (Wedge and Dash representations according to Class XI Fig 6 |
1 | 5581-5584 | 8
Identify chiral and achiral molecules in each of the following pair of
compounds (Wedge and Dash representations according to Class XI Fig 6 6:
E is mirror image of D; E is rotated by 180o to get F and F is
non superimposable on its mirror image D |
1 | 5582-5585 | (Wedge and Dash representations according to Class XI Fig 6 6:
E is mirror image of D; E is rotated by 180o to get F and F is
non superimposable on its mirror image D However, the sign of optical rotation is not necessarily related to
the absolute (actual) configuration of the molecule |
1 | 5583-5586 | Fig 6 6:
E is mirror image of D; E is rotated by 180o to get F and F is
non superimposable on its mirror image D However, the sign of optical rotation is not necessarily related to
the absolute (actual) configuration of the molecule Rationalised 2023-24
178
Chemistry
(iii) Retention: Retention of configuration is the preservation of the spatial
arrangement of bonds to an asymmetric centre during a chemical
reaction or transformation |
1 | 5584-5587 | 6:
E is mirror image of D; E is rotated by 180o to get F and F is
non superimposable on its mirror image D However, the sign of optical rotation is not necessarily related to
the absolute (actual) configuration of the molecule Rationalised 2023-24
178
Chemistry
(iii) Retention: Retention of configuration is the preservation of the spatial
arrangement of bonds to an asymmetric centre during a chemical
reaction or transformation In general, if during a reaction, no bond to the stereocentre is broken,
the product will have the same general configuration of groups
around the stereocentre as that of reactant |
1 | 5585-5588 | However, the sign of optical rotation is not necessarily related to
the absolute (actual) configuration of the molecule Rationalised 2023-24
178
Chemistry
(iii) Retention: Retention of configuration is the preservation of the spatial
arrangement of bonds to an asymmetric centre during a chemical
reaction or transformation In general, if during a reaction, no bond to the stereocentre is broken,
the product will have the same general configuration of groups
around the stereocentre as that of reactant Such a reaction is said
to proceed with retention of the configuration |
1 | 5586-5589 | Rationalised 2023-24
178
Chemistry
(iii) Retention: Retention of configuration is the preservation of the spatial
arrangement of bonds to an asymmetric centre during a chemical
reaction or transformation In general, if during a reaction, no bond to the stereocentre is broken,
the product will have the same general configuration of groups
around the stereocentre as that of reactant Such a reaction is said
to proceed with retention of the configuration Consider as an
example, the reaction that takes place when (–)-2-methylbutan-1-ol
is heated with concentrated hydrochloric acid |
1 | 5587-5590 | In general, if during a reaction, no bond to the stereocentre is broken,
the product will have the same general configuration of groups
around the stereocentre as that of reactant Such a reaction is said
to proceed with retention of the configuration Consider as an
example, the reaction that takes place when (–)-2-methylbutan-1-ol
is heated with concentrated hydrochloric acid Solution
Solution
Solution
Solution
Solution
It is important to note that configuration at a symmetric centre in
the reactant and product is same but the sign of optical rotation
has changed in the product |
1 | 5588-5591 | Such a reaction is said
to proceed with retention of the configuration Consider as an
example, the reaction that takes place when (–)-2-methylbutan-1-ol
is heated with concentrated hydrochloric acid Solution
Solution
Solution
Solution
Solution
It is important to note that configuration at a symmetric centre in
the reactant and product is same but the sign of optical rotation
has changed in the product This is so because two different
compounds with same configuration at asymmetric centre may have
different optical rotation |
1 | 5589-5592 | Consider as an
example, the reaction that takes place when (–)-2-methylbutan-1-ol
is heated with concentrated hydrochloric acid Solution
Solution
Solution
Solution
Solution
It is important to note that configuration at a symmetric centre in
the reactant and product is same but the sign of optical rotation
has changed in the product This is so because two different
compounds with same configuration at asymmetric centre may have
different optical rotation One may be dextrorotatory (plus sign of
optical rotation) while other may be laevorotatory (negative sign of
optical rotation) |
1 | 5590-5593 | Solution
Solution
Solution
Solution
Solution
It is important to note that configuration at a symmetric centre in
the reactant and product is same but the sign of optical rotation
has changed in the product This is so because two different
compounds with same configuration at asymmetric centre may have
different optical rotation One may be dextrorotatory (plus sign of
optical rotation) while other may be laevorotatory (negative sign of
optical rotation) (iv) Inversion, retention and racemisation: There are three outcomes
for a reaction at an asymmetric carbon atom, when a bond directly
linked to an asymmetric carbon atom is broken |
1 | 5591-5594 | This is so because two different
compounds with same configuration at asymmetric centre may have
different optical rotation One may be dextrorotatory (plus sign of
optical rotation) while other may be laevorotatory (negative sign of
optical rotation) (iv) Inversion, retention and racemisation: There are three outcomes
for a reaction at an asymmetric carbon atom, when a bond directly
linked to an asymmetric carbon atom is broken Consider the
replacement of a group X by Y in the following reaction;
If (A) is the only compound obtained, the process is called retention
of configuration |
1 | 5592-5595 | One may be dextrorotatory (plus sign of
optical rotation) while other may be laevorotatory (negative sign of
optical rotation) (iv) Inversion, retention and racemisation: There are three outcomes
for a reaction at an asymmetric carbon atom, when a bond directly
linked to an asymmetric carbon atom is broken Consider the
replacement of a group X by Y in the following reaction;
If (A) is the only compound obtained, the process is called retention
of configuration Note that configuration has been rotated in A |
1 | 5593-5596 | (iv) Inversion, retention and racemisation: There are three outcomes
for a reaction at an asymmetric carbon atom, when a bond directly
linked to an asymmetric carbon atom is broken Consider the
replacement of a group X by Y in the following reaction;
If (A) is the only compound obtained, the process is called retention
of configuration Note that configuration has been rotated in A If (B) is the only compound obtained, the process is called inversion
of configuration |
1 | 5594-5597 | Consider the
replacement of a group X by Y in the following reaction;
If (A) is the only compound obtained, the process is called retention
of configuration Note that configuration has been rotated in A If (B) is the only compound obtained, the process is called inversion
of configuration Configuration has been inverted in B |
1 | 5595-5598 | Note that configuration has been rotated in A If (B) is the only compound obtained, the process is called inversion
of configuration Configuration has been inverted in B Rationalised 2023-24
179 Haloalkanes and Haloarenes
If a 50:50 mixture of A and B is obtained then the process is called
racemisation and the product is optically inactive, as one isomer will
rotate the plane polarised light in the direction opposite to another |
1 | 5596-5599 | If (B) is the only compound obtained, the process is called inversion
of configuration Configuration has been inverted in B Rationalised 2023-24
179 Haloalkanes and Haloarenes
If a 50:50 mixture of A and B is obtained then the process is called
racemisation and the product is optically inactive, as one isomer will
rotate the plane polarised light in the direction opposite to another Now let us have a fresh look at SN1 and SN2 mechanisms by
taking examples of optically active alkyl halides |
1 | 5597-5600 | Configuration has been inverted in B Rationalised 2023-24
179 Haloalkanes and Haloarenes
If a 50:50 mixture of A and B is obtained then the process is called
racemisation and the product is optically inactive, as one isomer will
rotate the plane polarised light in the direction opposite to another Now let us have a fresh look at SN1 and SN2 mechanisms by
taking examples of optically active alkyl halides In case of optically active alkyl halides, the product formed as a
result of SN2 mechanism has the inverted configuration as compared
to the reactant |
1 | 5598-5601 | Rationalised 2023-24
179 Haloalkanes and Haloarenes
If a 50:50 mixture of A and B is obtained then the process is called
racemisation and the product is optically inactive, as one isomer will
rotate the plane polarised light in the direction opposite to another Now let us have a fresh look at SN1 and SN2 mechanisms by
taking examples of optically active alkyl halides In case of optically active alkyl halides, the product formed as a
result of SN2 mechanism has the inverted configuration as compared
to the reactant This is because the nucleophile attaches itself on the
side opposite to the one where the halogen atom is present |
1 | 5599-5602 | Now let us have a fresh look at SN1 and SN2 mechanisms by
taking examples of optically active alkyl halides In case of optically active alkyl halides, the product formed as a
result of SN2 mechanism has the inverted configuration as compared
to the reactant This is because the nucleophile attaches itself on the
side opposite to the one where the halogen atom is present When
(–)-2-bromooctane is allowed to react with sodium hydroxide,
(+)-octan-2-ol is formed with the –OH group occupying the position
opposite to what bromide had occupied |
1 | 5600-5603 | In case of optically active alkyl halides, the product formed as a
result of SN2 mechanism has the inverted configuration as compared
to the reactant This is because the nucleophile attaches itself on the
side opposite to the one where the halogen atom is present When
(–)-2-bromooctane is allowed to react with sodium hydroxide,
(+)-octan-2-ol is formed with the –OH group occupying the position
opposite to what bromide had occupied Thus, SN2 reactions of optically active halides are accompanied by
inversion of configuration |
1 | 5601-5604 | This is because the nucleophile attaches itself on the
side opposite to the one where the halogen atom is present When
(–)-2-bromooctane is allowed to react with sodium hydroxide,
(+)-octan-2-ol is formed with the –OH group occupying the position
opposite to what bromide had occupied Thus, SN2 reactions of optically active halides are accompanied by
inversion of configuration In case of optically active alkyl halides, SN1 reactions are
accompanied by racemisation |
1 | 5602-5605 | When
(–)-2-bromooctane is allowed to react with sodium hydroxide,
(+)-octan-2-ol is formed with the –OH group occupying the position
opposite to what bromide had occupied Thus, SN2 reactions of optically active halides are accompanied by
inversion of configuration In case of optically active alkyl halides, SN1 reactions are
accompanied by racemisation Can you think of the reason why it
happens |
1 | 5603-5606 | Thus, SN2 reactions of optically active halides are accompanied by
inversion of configuration In case of optically active alkyl halides, SN1 reactions are
accompanied by racemisation Can you think of the reason why it
happens Actually the carbocation formed in the slow step being sp
2
hybridised is planar (achiral) |
1 | 5604-5607 | In case of optically active alkyl halides, SN1 reactions are
accompanied by racemisation 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) |
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