Unit 14: Applications of Organic Chemistry
Assignment C: Designing molecules.
Explain the different types of structural isomerism and stereoisomerism. (P4)
Isomers: An isomer is a molecule with the same molecular formula but arranged differently in space.
Those arrangements will not be affected by the rotation of the molecule as a whole, or by the
rotation of individual bonds within the molecule. Here are two examples of molecules that are the
same. Neither of them is an isomer. They are both butane.
This molecule can also twist itself in an endless number of ways. Single carbon-carbon bonds can
rotate freely around each other.
Structural isomerism:
As the name implies, structural isomers have the same molecular formula but are arranged in a
different order.
The different connectivity between molecules have the same kind of molecular formula but differ in
order of their assembly. As one example of a structural isomer with different isomers, Alkane
(C4H10) can be viewed as an example of a simple structural isomer. The structural isomers of an
alkane molecule increase as its carbon content increases.
Types of structural isomerism:
Chain isomerism: When a carbon atom is arranged differently from its neighbouring carbon
atoms, chain isomerism occurs. Chain isomerism occurs when two or more compounds
exhibit the same molecular formula with different main chains. Skeletal isomerism is also
known as this phenomenon.
Name Structural formula 3D Structural formula
Pentane
, Neopentane
It is due to branching in carbon chains that these isomers arise. Pentane, C5H10, has three
isomers. The carbon atoms in one of them form a "straight chain," while those in the others
form a branched chain.
Position Isomerism: When substituent atoms or groups of atoms are occupying different
positions or when a chain is unsaturated, positional isomerism results. Isomerism occurs
when the position of functional groups with respect to main chain atoms changes.
First example: Position of a double bond in alkenes:
Positional Isomers in C5H12
Name Structural formula 3D Structural formula
1-bromopropane
2-bromopropane
, With the molecular formula C3H7Br, there are two structural isomers. Bromine atoms are attached
at the ends of one chain and at the middle of the other.
Models cannot be twisted to turn one molecule into another. In order to reattach the bromine, you
would need to break it off at the end and reconnect it at the middle. In addition, there would be a
hydrogen that would need to be moved between the middle and the end at the same time.
Alcohols such as C4H9OH are another example of similar compounds
Name Structural formula 3D Structural formula
Butan-1-ol
Butan-2-ol
Providing you stick to a four-carbon chain, these are the only two options, but this isn't necessary.
Position and chain isomerism can both be mixed - they aren't mutually exclusive.
Function Group Isomerism: When functional groups with the same chemical formula have
an odd form, it is known as functional group isomerism. The concept of functional isomerism
Assignment C: Designing molecules.
Explain the different types of structural isomerism and stereoisomerism. (P4)
Isomers: An isomer is a molecule with the same molecular formula but arranged differently in space.
Those arrangements will not be affected by the rotation of the molecule as a whole, or by the
rotation of individual bonds within the molecule. Here are two examples of molecules that are the
same. Neither of them is an isomer. They are both butane.
This molecule can also twist itself in an endless number of ways. Single carbon-carbon bonds can
rotate freely around each other.
Structural isomerism:
As the name implies, structural isomers have the same molecular formula but are arranged in a
different order.
The different connectivity between molecules have the same kind of molecular formula but differ in
order of their assembly. As one example of a structural isomer with different isomers, Alkane
(C4H10) can be viewed as an example of a simple structural isomer. The structural isomers of an
alkane molecule increase as its carbon content increases.
Types of structural isomerism:
Chain isomerism: When a carbon atom is arranged differently from its neighbouring carbon
atoms, chain isomerism occurs. Chain isomerism occurs when two or more compounds
exhibit the same molecular formula with different main chains. Skeletal isomerism is also
known as this phenomenon.
Name Structural formula 3D Structural formula
Pentane
, Neopentane
It is due to branching in carbon chains that these isomers arise. Pentane, C5H10, has three
isomers. The carbon atoms in one of them form a "straight chain," while those in the others
form a branched chain.
Position Isomerism: When substituent atoms or groups of atoms are occupying different
positions or when a chain is unsaturated, positional isomerism results. Isomerism occurs
when the position of functional groups with respect to main chain atoms changes.
First example: Position of a double bond in alkenes:
Positional Isomers in C5H12
Name Structural formula 3D Structural formula
1-bromopropane
2-bromopropane
, With the molecular formula C3H7Br, there are two structural isomers. Bromine atoms are attached
at the ends of one chain and at the middle of the other.
Models cannot be twisted to turn one molecule into another. In order to reattach the bromine, you
would need to break it off at the end and reconnect it at the middle. In addition, there would be a
hydrogen that would need to be moved between the middle and the end at the same time.
Alcohols such as C4H9OH are another example of similar compounds
Name Structural formula 3D Structural formula
Butan-1-ol
Butan-2-ol
Providing you stick to a four-carbon chain, these are the only two options, but this isn't necessary.
Position and chain isomerism can both be mixed - they aren't mutually exclusive.
Function Group Isomerism: When functional groups with the same chemical formula have
an odd form, it is known as functional group isomerism. The concept of functional isomerism
