Unit 14b: Designing molecules
Introduction:
Isomerism is a fundamental concept in chemistry that refers to the existence of different
structures with the same molecular formula. Isomerism can occur in two forms: structural
isomerism and stereoisomerism. Structural isomerism arises from differences in the
connectivity of atoms within a molecule, while stereoisomerism results from differences in
the spatial arrangement of atoms within a molecule. Isomerism plays a crucial role in
various aspects of chemistry, including drug development, organic synthesis, and materials
science, among others. In this assignment, we will explore the importance and impact of
isomerism in industry, focusing on case studies that examine the formation of different
isomers during manufacture, their influence on the industrial process, the differences in
their properties, and the possible consequences of ignoring the presence of isomerism. We
will also analyse the therapeutic and chemical effects of isomerism using the drugs
thalidomide and ibuprofen as examples, comparing their structures and properties of the
optical isomers in each case study, and discussing the implications of having to separate a
racemic mixture into its stereoisomers.
Structural isomerism
Structural isomerism is a type of isomerism where molecules with the same molecular
formula have different arrangements of atoms in their structures. This occurs when the
atoms in a molecule are connected in different ways, resulting in different physical and
chemical properties.
There are three main types of structural isomerism: chain isomerism, positional isomerism,
and functional group isomerism.
Chain isomerism:
Chain isomers have the same molecular formula but differ in the arrangement of the carbon
chain. This type of isomerism is often observed in hydrocarbons, which can have linear or
branched chains.
In chain isomerism, the carbon skeleton of the molecule is different. For example, butane
(C4H10) and 2-methylpropane (C4H10) are chain isomers because they have different
arrangements of the carbon chain.
,Butane and 2-methylpropane: Both of these molecules have the molecular formula C4H10,
but they have different structures due to chain isomerism. Butane has a linear chain of four
carbon atoms, while 2-methylpropane has a branched chain with one carbon atom attached
to the second carbon atom of the chain. As a result, butane has a higher boiling point and
melting point than 2-methylpropane due to stronger intermolecular forces of attraction
between its linear molecules.
Positional isomerism:
Positional isomers have the same molecular formula but differ in the position of functional
groups or substituents on the carbon chain.
In positional isomerism, the functional groups or substituents are attached to different
positions on the carbon chain. For example, pentan-1-ol (C5H12O) and pentan-2-ol
(C5H12O) are positional isomers because they have the same molecular formula but
different positions of the hydroxyl group.
Pentan-1-ol and pentan-2-ol: Both of these molecules have the molecular formula C5H12O,
but they have different structures due to positional isomerism. Pentan-1-ol has the hydroxyl
, group attached to the first carbon atom of the chain, while pentan-2-ol has the hydroxyl
group attached to the second carbon atom of the chain. Pentan-1-ol has a higher boiling
point than pentan-2-ol because the hydroxyl group is better able to form hydrogen bonds
with other molecules due to its position on the end of the molecule.
Functional group isomerism:
Functional group isomers have the same molecular formula but differ in the functional
group attached to the carbon chain. This type of isomerism is commonly observed in organic
compounds.
In functional group isomerism, the functional groups of the molecules are different. For
example, propanal (C3H6O) and propanone (C3H6O) are functional group isomers because
they have the same molecular formula but different functional groups (aldehyde and
ketone, respectively).
Propanal and propanone: Both of these molecules have the molecular formula C3H6O, but
they have different structures due to functional group isomerism. Propanal is an aldehyde,
while propanone is a ketone. Aldehydes and ketones have different physical and chemical
properties due to differences in their functional groups. For example, aldehydes tend to be
more reactive and have a stronger odour than ketones.
Stereoisomerism
Stereoisomerism refers to the phenomenon where molecules have the same molecular
formula and the same connectivity of atoms, but differ in their spatial arrangement of
atoms. There are two main types of stereoisomerism: geometric isomerism and optical
isomerism.
Geometric isomerism
In geometric isomerism, the stereoisomers differ in their geometric arrangement around a
double bond or a ring. There are two types of geometric isomers: cis (Z) and trans (E)
Introduction:
Isomerism is a fundamental concept in chemistry that refers to the existence of different
structures with the same molecular formula. Isomerism can occur in two forms: structural
isomerism and stereoisomerism. Structural isomerism arises from differences in the
connectivity of atoms within a molecule, while stereoisomerism results from differences in
the spatial arrangement of atoms within a molecule. Isomerism plays a crucial role in
various aspects of chemistry, including drug development, organic synthesis, and materials
science, among others. In this assignment, we will explore the importance and impact of
isomerism in industry, focusing on case studies that examine the formation of different
isomers during manufacture, their influence on the industrial process, the differences in
their properties, and the possible consequences of ignoring the presence of isomerism. We
will also analyse the therapeutic and chemical effects of isomerism using the drugs
thalidomide and ibuprofen as examples, comparing their structures and properties of the
optical isomers in each case study, and discussing the implications of having to separate a
racemic mixture into its stereoisomers.
Structural isomerism
Structural isomerism is a type of isomerism where molecules with the same molecular
formula have different arrangements of atoms in their structures. This occurs when the
atoms in a molecule are connected in different ways, resulting in different physical and
chemical properties.
There are three main types of structural isomerism: chain isomerism, positional isomerism,
and functional group isomerism.
Chain isomerism:
Chain isomers have the same molecular formula but differ in the arrangement of the carbon
chain. This type of isomerism is often observed in hydrocarbons, which can have linear or
branched chains.
In chain isomerism, the carbon skeleton of the molecule is different. For example, butane
(C4H10) and 2-methylpropane (C4H10) are chain isomers because they have different
arrangements of the carbon chain.
,Butane and 2-methylpropane: Both of these molecules have the molecular formula C4H10,
but they have different structures due to chain isomerism. Butane has a linear chain of four
carbon atoms, while 2-methylpropane has a branched chain with one carbon atom attached
to the second carbon atom of the chain. As a result, butane has a higher boiling point and
melting point than 2-methylpropane due to stronger intermolecular forces of attraction
between its linear molecules.
Positional isomerism:
Positional isomers have the same molecular formula but differ in the position of functional
groups or substituents on the carbon chain.
In positional isomerism, the functional groups or substituents are attached to different
positions on the carbon chain. For example, pentan-1-ol (C5H12O) and pentan-2-ol
(C5H12O) are positional isomers because they have the same molecular formula but
different positions of the hydroxyl group.
Pentan-1-ol and pentan-2-ol: Both of these molecules have the molecular formula C5H12O,
but they have different structures due to positional isomerism. Pentan-1-ol has the hydroxyl
, group attached to the first carbon atom of the chain, while pentan-2-ol has the hydroxyl
group attached to the second carbon atom of the chain. Pentan-1-ol has a higher boiling
point than pentan-2-ol because the hydroxyl group is better able to form hydrogen bonds
with other molecules due to its position on the end of the molecule.
Functional group isomerism:
Functional group isomers have the same molecular formula but differ in the functional
group attached to the carbon chain. This type of isomerism is commonly observed in organic
compounds.
In functional group isomerism, the functional groups of the molecules are different. For
example, propanal (C3H6O) and propanone (C3H6O) are functional group isomers because
they have the same molecular formula but different functional groups (aldehyde and
ketone, respectively).
Propanal and propanone: Both of these molecules have the molecular formula C3H6O, but
they have different structures due to functional group isomerism. Propanal is an aldehyde,
while propanone is a ketone. Aldehydes and ketones have different physical and chemical
properties due to differences in their functional groups. For example, aldehydes tend to be
more reactive and have a stronger odour than ketones.
Stereoisomerism
Stereoisomerism refers to the phenomenon where molecules have the same molecular
formula and the same connectivity of atoms, but differ in their spatial arrangement of
atoms. There are two main types of stereoisomerism: geometric isomerism and optical
isomerism.
Geometric isomerism
In geometric isomerism, the stereoisomers differ in their geometric arrangement around a
double bond or a ring. There are two types of geometric isomers: cis (Z) and trans (E)
