UNIT 14C Chemistry
Molecules that have the same molecular formula, but different arrangements
of atoms are called isomers. This makes the isomers have different chemical or
physical properties. There are two main kinds of isomers: stereoisomerism and
structural isomerism.
Structural isomerism
In this type of isomerism, the atoms are arranged in a completely different
order. This means that they have the same molecular formula but different
structural formulae. For example, the molecular formula of propane is C 3H8
but its structural formula is CH3CH2CH3. Structural isomers are divided into
different types known as chain, positional and functional groups isomerism.
Chain isomerism
Chain isomerism is when there is a different atomic arrangement of the
carbon-carbon chain of a molecule. The positioning of the carbon atoms in a
molecule is arranged differently to make carbon chains that are branched off
the main chain. Chain isomers have different IUPAC names, but the molecular
formula stays the same. For example, butane and methylpropane have the
same molecular formula but different arrangements of atoms/carbon chains.
Positional isomerism
Positional isomers are molecules that have the same functional group but are
placed in a different position. Here the basic carbon skeleton is not changed
, but the important groups on that skeleton are moved around. Even here to
reflect this change in position of the functional group the IUPAC name of the
molecule changes, but like chain isomerism, the molecular formula says the
same. Propan-1-ol and propan-2-ol, for example, are positional isomers. Their
carbon chains are identical, but in each case the -OH group is connected to a
different carbon.
Sometimes both chain and positional isomers are present. And positional
isomerism can occur in benzene rings. For example, the molecule C 7H7Cl can
have four different isomers based on where the chlorine atom is position
Functional group isomerism
This is when the atoms in a molecule are rearranged to different positions to
give different functional groups. The isomers contain different functional
groups (they belong to different homologous series). For example, a molecular
formula with C3H6O can either be propane or propanone.
Molecules that have the same molecular formula, but different arrangements
of atoms are called isomers. This makes the isomers have different chemical or
physical properties. There are two main kinds of isomers: stereoisomerism and
structural isomerism.
Structural isomerism
In this type of isomerism, the atoms are arranged in a completely different
order. This means that they have the same molecular formula but different
structural formulae. For example, the molecular formula of propane is C 3H8
but its structural formula is CH3CH2CH3. Structural isomers are divided into
different types known as chain, positional and functional groups isomerism.
Chain isomerism
Chain isomerism is when there is a different atomic arrangement of the
carbon-carbon chain of a molecule. The positioning of the carbon atoms in a
molecule is arranged differently to make carbon chains that are branched off
the main chain. Chain isomers have different IUPAC names, but the molecular
formula stays the same. For example, butane and methylpropane have the
same molecular formula but different arrangements of atoms/carbon chains.
Positional isomerism
Positional isomers are molecules that have the same functional group but are
placed in a different position. Here the basic carbon skeleton is not changed
, but the important groups on that skeleton are moved around. Even here to
reflect this change in position of the functional group the IUPAC name of the
molecule changes, but like chain isomerism, the molecular formula says the
same. Propan-1-ol and propan-2-ol, for example, are positional isomers. Their
carbon chains are identical, but in each case the -OH group is connected to a
different carbon.
Sometimes both chain and positional isomers are present. And positional
isomerism can occur in benzene rings. For example, the molecule C 7H7Cl can
have four different isomers based on where the chlorine atom is position
Functional group isomerism
This is when the atoms in a molecule are rearranged to different positions to
give different functional groups. The isomers contain different functional
groups (they belong to different homologous series). For example, a molecular
formula with C3H6O can either be propane or propanone.
