Alcohols Flashcards
what functional group do alcohols contain?
the hydroxyl functional group
what is meant by the term functional group?
Atom/group of atoms that give molecules their characteristic for reactions
What is the general formula for aliphatic alcohols with one OH group only?
CnH(2n+2)O
what are phenols?
Aromatic alcohols
Where is the OH group attached to on phenol?
alcohol group directly attached directly to the benzene ring
why can alcohols make hydrogen bonds with water molecules and with each other?
because they have H bonded to electronegative O
What does hydrogen bond between alcohol molecules do?
reduces their volatility (the ease of conversion from liquid to gas)
what the more OH groups that alcohol has result in?
The more hydrogen bonds it can form and the lower of volatility
why do alcohols have a tendency to be water soluble?
Because they can form hydrogen bonds
what does solubility decrease with?
Solubility decreases as the hydrocarbon chain increases
what causes solubility to decrease as the hydrocarbon chain increases is size?
The OH group has less influence and the solubility (lack of) of the longer hydrocarbon chain beccomes more dominant
What is a primary alcohol?
The -OH group is attached to a C with at least two H atoms on it and one alkyl group
What are secondary alcohols?
The -OH group is attached to a carbon atom with only one H atom on it and two alkyl groups.
what are tertiary alcohols?
The -OH group is attached to a carbon atom with no H atoms on it and three alkyl groups.
what are the four types of chemical reactions of the alcohols?
-Combustion
-Dehydration
-Substitution
-Oxidation
What is combustion of alcohol?
like organic materials, alcohols burn in excess oxygen to produce carbon dioxide and water
What does the term dehydration mean?
to remove water from one molecule
what is a good dehydrating agent?
Concentrated sulphuric acid or concentrated phosphoric acid
what are the conditions for dehydration of alcohol?
Heat under reflux
What does dehydration make?
An Alkene
Why is dehydration described as elimination?
because H and OH are being taken out from two adjacent c atoms to make water
what is substitution reactions of alcohol?
-Alcohols can form when you react with hydrogen halide
-The hydrogen halide is generated in place
what is an example of substitution reactions of alcohol?
An alcohol is heated, under reflux, in the presence of sodium chlorine and dilute sulphuric , hydrogen chloride forms in situ (in place)
Why do chemical reactions usually need to be heated?
in order to overcome activation energy and increase the rate of reaction
what is reflux commonly used to do?
to prepare organic liquids without boiling off the solvent, reactants or products.
In the reflux, why is the condenser in an upright position and never a stopper/thermometer at the top?
This would create a closed system
why is distillation a commonly used part of the purification of organic liquid?
it separates a pure liquid from its impurities by collecting at the boiling point of the pure liquid
What is another use of distillation?
to produce an aldehyde, rather than a carboxylic acid when oxidising a primary alcohol
how can primary and secondary alcohols oxidised?
using oxidising agents potassium dichromate, in dilute sulphuric acid
What are primary alcohols oxidised to? (loss of H)
Aldehydes
What does [O] represent in the oxidation of alcohols?
Oxidising agent
Why would you heat alcohol under distillation conditions in oxidation?
So the lower boiling point aldehyde (no H bonds) distils out of the reaction mixture as it forms
what would happen if acidified potassium dichromate was used as the oxidising reagent in oxidation?
A quick change from Orange to Green will occur in this reaction (because dichromate is being reduced to chromium (III)
What can occur if the oxidising agent is used in excess (oxidation)?
further oxidation can occur to give a carboxylic acid
why would you heat oxidation of alcohols under reflux?
so that any alcohol in the initially made goes back into the flask to be further oxidised
how can secondary alcohols be oxidised?
they can be oxidised in a similar way to primary alcohols to form ketones
why does further oxidation not occur in secondary alcohols?
Ketones cannot be oxidised
Can tertiary alcohols be oxidised?
No
