Alcohols Flashcards
What is the functional group of alcohols, and what is the general formula?
-OH
CnH2n+1OH
Explain the difference between a primary, secondary and tertiary alcohol
Primary : ( 1 carbon )
Alcohol bonded to carbon which is bonded to one alkyl group
Secondary : ( 2 carbon )
Alcohol bonded to the carbon which is bonded to 2 alkyl groups
Tertiary : ( 3 carbon )
Alcohol bonded to the carbon which is bonded to 3 alkyl groups
What does the solubility of alcohols depend on why?
It has an OH group so can form hydrogen bonds with water. But, the longer the hydrocarbon chain, the more insoluble the alcohol is. Carbon chain is NON POLAR and HYDROPHOBIC and reduces interaction of alcohol with water
Therefore less water soluble as chain length increases
Why are alcohols polar? What property does this give alcohols?
It has an O-H bond so there is a difference in electronegativity. Slightly positive and negative oxygen. Electrons are therefore pulled towards the ELECTRONEGATIVE oxygen in the covalent bond.
This means alcohols are soluble because the lone pair on oxygen atoms forms a hydrogen bond with water.
Why do alcohols have a high boiling point?
They can hydrogen bond with each other. Hydrogen bonding is the STRONGEST intermolecular force.
Give examples of alcohols which are soluble in water
Smaller carbons, up to 3 carbons. For example, methanol, ethanol, propan-1-ol
What is volatility? Why are alcohols LESS volatile than alkanes?
Volatility is a substances capability of readily changing from a solid/liquid into a gas. More energy is needed to overcome the hydrogen bonds BETWEEN MOLECULES in alcohols than the weaker London forces in alkanes. Hydrogen bonding is STRONGER than London forces.
What is formed when hydrogen hallides react with alcohol? How can we ensure it is a haloalkane? Conditions?
Halogenoalkanes / haloalkanes are made when an alcohol reacts with a halide ion. SUBSTITUTION
Heat under reflux with an acid catalyst is used (sulphuric acid) and a sodium halide. This produces a hydrogen hallide in situ to react with the alcohol.
We can use a pH meter to detect an alkaline solution.
How are alkenes made from alcohols, and state conditions? Give one reason why people would use this reaction in industries?
Dehydration
The removal of water causes an alkene to be formed.
Conditions :
Conc h2so4
170-180 degrees
This is an elimination reaction, where an alkene and water is formed.
This reaction is used to make polymers which are used to make plastics.
Explain how EZ isomers can be formed in dehydration
The double bond can be formed on either side of the carbon that had the hydroxyl group. .
Explain the combustion of alcohols. What use does this give them?
Alcohols are readily combusted and OXIDISED and form CO2 & H2O. They burn readily and with a light blue flame. They can be used as fuels to generate energy.
Exothermic
What are primary alcohols oxidised to?
Aldehydes then carboxylic acids.
What are the three substances alcohols can be oxidised into? What is used for their oxidation?
Aldehydes, ketones and carboxylic acids.
We heat the reaction mixture with mild oxidising acidified agent potassium chromate ( K2Cr2O7 ) - it is REDUCED itself and the alcohols are oxidised. It turns from the orange dichromate ion to the green chromium ion.
Describe the structure of a aldehyde
It has a C-H group and C=O group on the end carbon. It ends in -al and will have CHO in the molecular formula.
Describe the structure of a carboxylic acid
It ends in -oic, it has a C=O and C-OH group. The molecule formula has COOH.
What process is used to oxidise tertiary alcohols?
No oxidation with use of potassium dichromate ion, will remain orange
What can secondary alcohols be oxidised into?
Ketones
What is reflux? What are the benefits of reflux?
This is when we heat the alcohol and the dehydrating/oxidising agent. This forms product which vaporises and passes into the condenser. The cooling water around the condenser causes the vapour to condense and go back into the flask to re react.
This allows strong heating without losing volatile reactants and products.
Describe the structure of ketones
It has a C=O group on the inner carbon ( or anywhere within the carbon chain ). Ends with -one
What process is used to extract an aldehyde from heating a primary alcohol in a boiling tube, and why?
We can use distillation because the aldehyde has a lower boiling point than the alcohol. This is to prevent it being oxidised into a carboxylic acid which would occur with stronger heating and further reacting with the alcohol. We heat the primary alcohol, vaporises and condenses
How do we make a carboxylic acid?
Reflux and excess oxidising agent.
How would you draw a dehydration reaction? What should you check for?
You would remove the hydroxyl group and an adjacent hydrogen atom. For carbon 2 and onwards, E and Z isomers can form because there are 2 different adjacent H atoms. S
How do we form halagenoalkanes from alcohols? Conditions?
This is formed by a substitution reaction when alcohols react with hydrogen halides.
Conditions :
- heat under reflux
- sodium halide ( NaCl, NaBr )
- sulphuric acid
The halogen is heated with sulphuric acid and a sodium halide under reflux. This produces a hydrogen hallide IN SITU, which then reacts with the alcohol.
How are primary alcohols oxidised by reflux?
When heated strongly, the aldehyde will remain in the flask due to reflux - this will cause it to be oxidised into a carboxylic acid.
We use excess oxidising agent in reflux to ensure ALL of the alcohol has reacted.
What type of combustion do alcohols undergo?
Complete combustion
Exothermic r
How is secondary alcohols oxidised? Why is this used over distillation?
Secondary alcohols are oxidised into ketones by heat under reflux. Reflux ensures ALL alcohol is reacted.
Why is Ethane-1,2-diol soluble in water? ( exam q )
It has OH groups
This means it can form hydrogen bonds with water
Why is Ethane-1,2-diol soluble in water? ( exam q )
It has OH groups
This means it can form hydrogen bonds with water
This is polar - lone pair on oxygen
How do you determine if an alcohol has a higher boiling point?
More OH groups = more hydrogen bonding = higher bp
Conditions and reagents for alcohols to haloalkanes? What reaction occurs?
Conditions :
H2so4
Reagents = Sodium halide
Nucleophilic substitution
What does a low volatility mean in terms of IMF?
High bp
