ALCOHOLS
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what are the bond angles in alcohols?
• all the H-C-H bonds and C-O are 109.5 (tetrahedral shape) - the H-O-C bond is 104.5 (bent line shape),
what is the reasoning behinds the bond angle in alcohols?
H-C-H there are 4 bonding pairs of electrons repelling to a position of minimum repulsion H-O-C there are 2 bonding pairs of electrons and 2 lone pairs repelling to a position of minimum repulsion. Lone pairs repel more than bonding pairs so the bond angle is reduced
is the boiling point of alcohols low or high and why?
The alcohols have relatively low volatility and high boiling points due to their ability to form hydrogen bond between alcohol molecules
can alcohols dissolve in water?
Smaller alcohols can dissolve in water because they can form hydrogen bonds to water molecules.
what is the difference between a primary, secondary and tertiary alcochol?
-Primary alcohols are alcohols where 1 carbon is attached to the carbon adjoining the oxygen. -Secondary alcohols are alcohols where 2 carbon are attached to the carbon adjoining the oxygen -Tertiary alcohols are alcohols where 3 carbon are attached to the carbon adjoining the oxygen.
what is the oxidising agent that causes alcohols to oxidise?
Potassium dichromate K2Cr2O7 is an oxidising agent that causes alcohols to oxidise.
what does the exact reaction of the oxidation of alcohols depend on?
The exact reaction, however, depends on the type of alcohol, i.e. whether it is primary, secondary, or tertiary, and on the conditions.
what is the reaction for the partial oxidation of alcohols?
primary alcohol -> aldehyde
what is the reagent for the partial oxidation of alcohols?
potassium dichromate (VI) solution and dilute sulfuric acid.
what are the conditions for the partial oxidation of alcohols?
(use a limited amount of dichromate) warm gently distil out the aldehyde as it forms:
what is the difference between an aldehyde and a ketone?
An aldehyde’s name ends in –al It always has the C=O bond on the first carbon of the chain so it does not need a number in its name WHEREAS Ketones end in -one When ketones have 5C’s or more in a chain then it needs a number to show the position of the double bond. E.g. pentan-2-one
what is distillation used for?
In general used as separation technique to separate an organic product from its reacting mixture.
how do we maximise yield in distillation?
In order to maximise yield collected, only collect the distillate at the approximate boiling point of the desired aldehyde and not higher.
where in the distillation apparatus should the bulb of the thermometer be and why?
The bulb of the thermometer should be at the T junction connecting to the condenser to measure the correct boiling point.
why does the water in the distillation apparatus go in to the bottom of the condenser and backwards?
• to go against gravity. This allows more efficient cooling and prevents back flow of water
what is used to heat organic chemicals and why?
Electric heaters are often used to heat organic chemicals. This is because organic chemicals are normally highly flammable and could set on fire with a naked flame
what can be done to the collection flask to improve the yield of the distillate?
The collection flask can be cooled in ice to help improve the yield of distillate
what is the reaction for the full oxidation of primary alcohols?
primary alcohol->carboxylic acid
what is the reagent for the full oxidation of primary alcohols?
potassium dichromate(VI) solution and dilute sulfuric acid
what are the conditions for the full oxidation of primary alcohols?
use an excess of dichromate heat under reflux: (distil off product after the reaction has finished)
what is the observation when a primary alcohol is partially oxidised?
Observation: the orange dichromate ion (Cr2O7 2-) reduces to the green Cr 3+ ion
what is the observation when a primary alcohol is fully oxidised?
Observation: the orange dichromate ion (Cr2O7 2-) reduces to the green Cr 3+ ion
when is reflux used?
Reflux is used when heating organic reaction mixtures for long periods.
what does the condenser in the reflux apparatus do?
The condenser prevents organic vapours from escaping by condensing them back to liquids.