Alcohols Flashcards
Describe an alcohol
- saturated containing only single covalent bonds
- have the formula CnH2n+1OH
- have a gradation in physical properties
- have similar chemical properties
How do you classified alcohols
- by where there functional group is in the chain
- primary
- secondary
- tertiary
How do you know that it is a primary alcohol
- a primary alcohol has the alcohol group attached to an end of the chain
- draw this
How do you know that it is a secondary alcohol
- a secondary alcohol has the alcohol group attached to a carbon atom with two alkyl chains and one hydrogen atom
- draw this
How do you know that it is a tertiary alcohol
- a tertiary alcohol has an alcohol group attached to a carbon atom with 3 alkyl chains attached
- draw this
Describe the trends of boiling points of alcohols
the boiling points of alcohols increase as the chain length increases, molecules get longer therefore there are more surface area contacts and there a stronger induced dipole-dipole intermolecular forces, therefore more energy is being needed to overcome the attractive forces and therefore a higher boiling points
Why are there boiling points of alcohols larger than there corresponding alkanes
- there are hydrogen bonds between alcohol molecules, these are the strongest type of intermolecular forces of attraction therefore a greater amount of energy is needed to overcome the force of the hydrogen bond therefore the boiling point of the alcohol is higher than that of the alkane
Describe the evaporation trends of alcohols
- volatility increases as the boiling point decreases, therefore shorter chains are more volatile then long chains
- alcohols have hydrogen bonds which make it less volatile then corresponding alkanes
Describe the solubility trends of alcohols
- water molecules are polar and so is the alcohol functional group therefore the molecules form hydrogen bonds with the molecules so they are soluble, this is described as miscibility
- as alcohol length increases the solubility of alcohol decreases
- the aliphatic chain cannot form hydrogen bonds and instead becomes part of the larger molecule
what are the products when alcohols are burnt
carbon dioxide and water
why is alcohol combusted
- alcohol can be used as fuels as they release there stored chemical energy in the form of thermal energy
What happens when you oxidise a tertiary alcohol
there is no reaction and potassium dichromate remains orange
What happens when a primary alcohol is oxidised, not under reflux
Aldehyde is produced and water
- heated with concentrated sulphuric acid, and potassium or sodium dichromate then distilled immediately
- the alcohol groups loses its hydrogen atoms and is partially oxidised
- colour change orange to green
- write the reaction for propan-1-ol
What happens when a primary alcohol is oxidised under reflux
Carboxylic acid is produced
- strongly heated with concentrated sulphuric acid and potassium or sodium dichromate
- full oxidation occurs
- write the reaction for propan-1-ol
What happens when secondary alcohol is heated under reflux
Ketone is produced
- strongly heated with concentrated sulphuric acid and potassium or sodium dichromate
- ketone does not undergo any more reaction
- write the reaction of butan-1-ol
What is esterification used for
to make an ester
What do you use to make an ester
carboxylic acid and alcohol
how do you make an ester
- react an alcohol with carboxylic acid in the presence of acid catalyst usually sulphuric acid, 8- degrees and sweet smell noticeable this is a reversible reaction and has a slow rate
- the O-H bond in the alcohol and the C-O bond in the carboxylic acid are broken, new bonds are made between the H and O-H to form water
- two remaining species bond to form the ester
Properties of ester
- small-molecule esters are soluble in water and many are visible as an oily layer floating on top of the reaction mixture
who names esters
IUPAC
How do you name esters
- first part is the name of the alkyl chain that was attached to the alcohol group
- the second part is the stem of the name of the carboxylic acid with the -oate on the end
Draw methyl ethanoate
DRAW IT
What is dehydration
- a chemical reaction in which water is lost from an organic compound this is an elimination reaction and it makes an alkene
Describe dehydration
alcohols are heated strongly and refluxed with concentrated sulphuric acid or another strong acid and 170 degrees, the water is eliminated, the OH group from one carbon atom and the H atom on an adjacent carbon atom lost to form a water molecule, the pie bond forms between the two adjacent carbon atoms
Draw dehydration of ethanol
draw it
What is halide substitution
- halide ions react with alcohols and the halide takes the place of the alcohol group to form the haloalkane
Describe Halide substitution
- react alcohol with a reagent which would be hydrogen halide like HCL or NaBr, this reacts with the sulphuric acid to make HBR
- acid catalyst like sulphuric acid is added and the mixture warmed to increase the rate of reaction
- however the iodide is reactant then phosphoric acid is used because the sulphuric acid oxidises iodide ions to iodine therefore it would make the yield of iodoalkane low
