This assignment attained a Distinction, with very detailed chemical and physical properties of a range of isomers, and the different types, compares, and analyses importance of isomerism with examples and true events to reinforce.
Applications of Organic Chemistry – Designing Molecules
Structural Isomerism
Compounds have the same molecular formula but different structural formulae due to a different
arrangement of atoms. There are three types of structural isomers.
Chain
Chain isomers are compounds with the same structural formulae but with different arrangements of the
carbon skeleton. They have similar chemical properties due to the same functional group, but slightly
different physical properties depending on degree of density and boiling point. If a compound has more
branching of carbons, they will have a lower boiling point, as branching reduces the effectiveness of
intermolecular forces, therefore less energy can break the molecules.
In 2-methylpropane the methyl group is branched to the second carbon. 2-methylpropane is a
colourless and odourless gas, which has a boiling point lower than Butane due to branching of -11.7
degrees. The melting point is -159.42 degrees. It has a density of 2.51 kg/m 3 at 15 degrees. It has a
solubility in water at 48.9 mg/L−1 at 25 degrees. When undergoing oxidation, it produces turt-butyl
hydro-peroxide and yields turt-butyl alcohol. The heat of combustion at gas and liquid state ranges from
-680-685kcal/mol at 25 degrees.
Butane is a noncyclical molecule; the methyl group is attached to the third carbon. Butane is a colourless
gas with a natural gas-like odour, it has a boiling point of -0.5 degrees, and a melting point of -140 to -
134 degrees. It has a density of 2.48 kg/m 3 at 15 degrees. It has a solubility in water at 61 mg/L at 20
degrees. Butane’s heat of combustion is at 2878 kJ/mol. When oxidised, butane burns and forms carbon
dioxide and water. The carbon to hydrogen bonds gives rise to dipole-dipole interactions. When broken,
they are not strong to overcome hydrogen bonds in water and therefore not miscible in water.
They both have a molecular formula of C4H10.
Pentane is a non-cyclical alkane with a straight chain, the methyl group is attached to the fourth carbon.
It appears as a colourless liquid with a gas-like odour. It has a density of 0.63 g/mL -1 at 20 degrees. It has
a melting point ranging from -130.5 to −129.1 degrees and a boiling point ranging from 35.9 to 36.3
degrees. It is soluble in water at 40 mg/L-1 at 20 degrees. Pentane is unreactive at standard room
temperature and conditions due to methyl groups being unreactive, but with activation energy, it
undergoes oxidation to form carbon dioxide and water. When in the gaseous state the heat of
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, Osman Yousuf
combustion is 3272 kJ/mol and when in the liquid state the heat of combustion is 3245 kJ/mol. The
carbon to hydrogen bonds gives rise to dipole-dipole interactions.
2-methylbutane is a compound which is branched with the methyl group attached to the third carbon. It
is a colourless liquid with a gas-like odour. It has a melting point ranging between -161 to -159 degrees
and a boiling point ranging from 27.8 to 28.2 degrees. The density of 2-methylbutane is at 606 mg/mL -1.
It is insoluble in water. It combusts at a heat of 3239 kJ/mol in the gaseous state and at 3264 kJ/mol in
the liquid state both at 20 degrees. It undergoes oxidation with potassium permanganate to produce
carbon dioxide, water, and 2-methylbutan-2-ol (an alcohol).
They both have a molecular formula of C5H12.
Positional
Positional isomers are compounds that have the same structural formula and carbon skeleton with the
same functional group, but the functional group is in a different position. They have similar chemical
properties and different physical properties.
Pent-1-ene and Pent-2-ene are alkenes with different placement of the double bonds. They both have a
molecular formula of C5H10.
In Pent-1-ene the double bond is between the first and second carbon. 1-pentene is a colourless liquid
with a gas-like odour. It has a boiling point of 30 degrees and a melting point of -165 degrees. It has a
low density of 0.64 g/mL at 25 degrees. It is insoluble in water as it is an alkene. The methyl groups give
1-pentene nonpolar and hydrophobic properties. Pent-1-ene combusts at heat ranging from 3100-
3300kJ/mol. It undergoes oxidation at the double bond with potassium permanganate to form carbon
dioxide, water and pent-1-ol (an alcohol). The position of the double bond makes pent-1-ene an alpha-
olefin and therefore makes the alkene more reactive. The double bond also enables the alkene to
undergo addition reactions.
In Pent-2-ene the double bond is between the second and third carbon atoms. 2-pentene can be cis or
trans due to geometric isomers. It is pictured below as trans pent-2-ene. This is a colourless liquid with a
hydrocarbon odour. It is insoluble in water due to nonpolar characteristics but soluble in organic
compounds. It has a density of 0.64 g/mL at 20 degrees. The boiling point is at 37 degrees and the
melting point at -140 degrees. It undergoes oxidation with potassium permanganate to produce
ethanoic acid and propanoic acid. It combusts at a heat between 3100-3500 degrees. The double bond
gives rise to addition reactions.
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