Unit 14 assignment 14.3
Learning aim c
What is an isomer?
An isomer is a chemical compound that has identical chemical formulae but differs in the
arrangement of atoms.there are many forms of isomerism and the following are an outline of some
if the isomers studied.
Functional Group Isomerism
Functional group isomers occur when two different homologous series of organic compounds have
the same molecular formula but different functional groups. is part of a molecule that is a group of
bonded atoms. This type of isomerism is very common to observe in organic chemistry.
In the example above we can see that propanal contains an aldehyde group that has a hydrogen
atom attached to the carboxyl group. As for the other example called propanone, this is classed as a
ketone with an alkyl or aryl group attached to the carbonyl group. Propanone will contain no
hydrogen atoms attached to its carbonyl group. Both of these examples have the chemical formula
of (CH3)2 CO and are both colourless and volatile. The boiling points of these two examples also
depend on how hydrogen bonding occurs. We can see this with propanone which has a boiling
point of 329 kelvin whereas propanol has a boiling point between 319-323 kelvin. So the hydrogen
bonds in propanone is slightly stronger so it takes more heat energy for the molecules to separate
and enter the gas phase. In industry, propanone is mainly used in the manufacture of plastics and
other products. An example is nail polish remover. Propanal is mainly used as a solvent.
Chain Isomerism
, The definition of a chain isomer is that two organic compounds have the same molecular formula
but they differ in the order in which the carbon atoms are bonded to each other.
As you can see from the above pentane has a chemical formula of C₅H₁₂ and neopentane (2,3
dimethyl propane) will also have the same chemical formula. The only difference is in the structures
of these two isomers. So on the neopentane, the CH3 is exchanged with the hydrogen atom along
with an additional CH3 on the right-hand side. This will vastly change the way the atoms are
bonded together and result in them having different properties and reactions.
One case we can use is that in neopentane the boiling point is 10 degrees celsius while pentane’s ist
36 degrees celsius. This is mainly because neopentane is more condensed and has less contact
surface area than pentane which will mean that pentane has more van der waals forces of attraction.
Pentane will have a higher melting point than its other isomer. This is because it can take on a rod-
like shape which allows the molecules to come closer to each other which will create stronger
intermolecular forces of attraction. For neopentane, it will melt or boil at lower melting or boiling
points as it will take on a spherical shape which enables the molecules to exert relatively little
attraction to each other. Regardless they are both combustible, colourless and lighter than water.
Positional isomers
Learning aim c
What is an isomer?
An isomer is a chemical compound that has identical chemical formulae but differs in the
arrangement of atoms.there are many forms of isomerism and the following are an outline of some
if the isomers studied.
Functional Group Isomerism
Functional group isomers occur when two different homologous series of organic compounds have
the same molecular formula but different functional groups. is part of a molecule that is a group of
bonded atoms. This type of isomerism is very common to observe in organic chemistry.
In the example above we can see that propanal contains an aldehyde group that has a hydrogen
atom attached to the carboxyl group. As for the other example called propanone, this is classed as a
ketone with an alkyl or aryl group attached to the carbonyl group. Propanone will contain no
hydrogen atoms attached to its carbonyl group. Both of these examples have the chemical formula
of (CH3)2 CO and are both colourless and volatile. The boiling points of these two examples also
depend on how hydrogen bonding occurs. We can see this with propanone which has a boiling
point of 329 kelvin whereas propanol has a boiling point between 319-323 kelvin. So the hydrogen
bonds in propanone is slightly stronger so it takes more heat energy for the molecules to separate
and enter the gas phase. In industry, propanone is mainly used in the manufacture of plastics and
other products. An example is nail polish remover. Propanal is mainly used as a solvent.
Chain Isomerism
, The definition of a chain isomer is that two organic compounds have the same molecular formula
but they differ in the order in which the carbon atoms are bonded to each other.
As you can see from the above pentane has a chemical formula of C₅H₁₂ and neopentane (2,3
dimethyl propane) will also have the same chemical formula. The only difference is in the structures
of these two isomers. So on the neopentane, the CH3 is exchanged with the hydrogen atom along
with an additional CH3 on the right-hand side. This will vastly change the way the atoms are
bonded together and result in them having different properties and reactions.
One case we can use is that in neopentane the boiling point is 10 degrees celsius while pentane’s ist
36 degrees celsius. This is mainly because neopentane is more condensed and has less contact
surface area than pentane which will mean that pentane has more van der waals forces of attraction.
Pentane will have a higher melting point than its other isomer. This is because it can take on a rod-
like shape which allows the molecules to come closer to each other which will create stronger
intermolecular forces of attraction. For neopentane, it will melt or boil at lower melting or boiling
points as it will take on a spherical shape which enables the molecules to exert relatively little
attraction to each other. Regardless they are both combustible, colourless and lighter than water.
Positional isomers
