Alcohols and Haloalkohols Flashcards
The boiling point of alcohols
Alcohol molecules are held together by hydrogen bonds which require a lot of energy to overcome, in order for the liquid to become a gas. This requires more energy then overcoming the weaker London forces in alkanes. Therefore alcohols have a lower volatility and a higher boiling point than alkanes with the same number of Carbon atoms.
Comparing alkanes and alcohols
Alkanes are non-polar because the electronegativity of carbon and hydrogen are very similar. The intermolecular forces are very weak London forces. Alcohols have a polar O-H bond because of the difference in electronegativity between the oxygen and hydrogen atoms alcohols are polar.
Volatility
the higher the boiling point the lower the volatility. It is the ability of a liquid to turn into a gas.
Alcohols solubility
Hydrogen bonds can form between the polar OH group and the water molecules meaning that the alcohol is soluble. Alkanes are non-polar molecules and can not form hydrogen bonds with the water. As the hydrocarbon chain increases in size the influence of the OH group becomes smaller and the solubility of the long chain alcohol becomes more like that of a hydrocarbon and solubility decreases.
Primary alcohol
When the Carbon attached to the OH group has two or three hydrogens attached
Secondary alcohols
When the carbon attached to the OH group has one hydrogen attached
Tertiary alcohols
When the carbon attached to the OH group has no hydrogens attached
Combustion of alcohols
Burns in oxygen to form CO2 and water.
Dehydration of alcohols
H2O can be eliminated from alcohols in the presence of phosphoric acid and heat to form an alkene
Substitution reactions of alcohols
The alcohol is heated under reflux with sulfuric acid and sodium bromide. The hydrogen bromide is formed in situ. The HBr reacts with the alcohol to produce the haloalkane, H2O is also released
Primary alcohol: full oxidation
The alcohol is turned into a carboxylic acid. You need excess acidified potassium dichromate. This is represented as 2[O]. It is under reflux. There is an orange to green colour change
Primary alcohol: Partial oxidation
The alcohol is turned into an aldehyde. There is a limited amount of acidified potassium dichromate. This is represented as [O]. The product is distilled out. There is an orange to green colour change.
Oxidation of secondary alcohols
The alcohol is turned into a ketone Done with acidified potassium dichromate under reflux. The oxidation reagent is demonstrated as [O]. There is an orange to green colour change
Oxidation of tertiary alcohols
They do not undergo oxidation so there will be no colour change
Acidified potassium dichromate
K2Cr2O7/ H+
