14 Alcohols Flashcards
What functional group do all alcohols contain?
-OH (hydroxyl group)
What is the functional group responsible for?
Physical and chemical properties of the alcohol
How do you name an alcohol?
Suffix -ol added to the stem name of the longest carbon chain
Position of -OH indicated
State the different in physical properties of the alcohols with alkanes (with the same number of carbon atoms)
Alcohols are:
Less volatile
Higher melting points
Greater water solubility
What happens to the difference in physical properties as the length of the carbon chain increases?
Become smaller
Define volatile
How readily something turns into a gas
Why do alcohols have higher melting points and are less volatile?
-Weak London forces
- Hydrogen bonds (strongest intermolecular bond relatively large amount of energy required to break)
Describe the polarity and intermolecular forces in alcohols
Polar O-H because of electronegativity difference so alcohol molecules are polar
Hence, also have stronger hydrogen bonds between the O-H groups
Why are alcohols soluble in water?
Hydrogen bonds form between the polar -OH group and the water molecules
Explain what happens to the solubility of alcohols as the chain increases
As the alkyl chain gets longer, the influence of the -OH group on the properties becomes less important
So bigger alcohols are more like corresponding alkane (solubility decreases)
What are the 3 classifications of alcohols?
Primary, secondary and tertiary
How do you classify alcohols as primary, secondary or tertiary?
Primary: carbon bonded to the -OH is bonded to 1 alkyl group and 2 hydrogens
Secondary: carbon bonded to the -OH is bonded to 2 alkyl group and 1 hydrogens
Tertiary: carbon bonded to the -OH group is bonded to 3 alkyl groups
What are the 4 reactions of alcohols?
Combustion
Oxidation (not adding oxygen!)
Dehydration
Substitution
Describe the combustion of alcohols and write a chemical equation for ethanol
Useful fuels
Burned in a plentiful supply of oxygen, energy released
C2H5OH +3O2 –> 2CO2 + 3H2O
What happens to the energy released in a combustion reaction as the chain increases?
As the number of carbon atoms in the chain gets bigger, the amount of energy released per mole also increases
What is the colour change if an alcohol is oxidised?
Orange to green
What is the oxidising agent for the oxidation of alcohols?
Potassium dichromate (VI) in sulphuric acid
What do primary alcohols oxidised on gentle heating and distillation?
Aldehyde
Give the displayed formula for the gentle heating of ethanol with potassium dichromate (VI) with sulphuric acid
OH H O
| | ||
CH3–C—H + [O] –> H–C–C—-H +H2O
| |
H H
Ethanol –> Ethanal
What do primary alcohol oxidise to under reflux and excess acidified potassium dichromate?
Carboxylic acid
Draw an equation for the oxidation of propanol-1-ol under reflux
CH3CH2CH2(OH) +2[O] –> CH3CH2COOH + H2O
Propanoic acid
Why does there need to be excess acidified potassium dichromate (VI) and reflux?
Excess ensures that all the alcohol reacts
Heating under reflux ensures that the aldehyde undergoes further oxidation all the way to the carboxylic acid
What do secondary alcohols oxidise and under what conditions?
Ketones
Reflux - guarantee reaction is finished
Not possible to oxidise ketones any further
Draw an equation for the oxidation of propan-2-ol
CH3CH(OH)CH3 + [O] –> CH3COCH3 +H2O
What do tertiary alcohols oxidise to and why?
Do not undergo oxidation!!!
Would require breaking of a C-C bond
What is dehydration of alcohols?
Involves losing a molecule of water to form an alkene
What are the conditions for dehydration?
Concentrated phosphoric acid as a catalyst
Draw an equation for the dehydration of propan-1-ol
CH3CH2CH2(OH) –> CH3CH2CH2 + H2O
Propan-1-ol –> propene and water
What type of reaction is a dehydration?
Elimination (opposite of an addition reaction)
What are the 2 reactions for a substitution reaction?
Heated under reflux with sulfuric acid and sodium bromide, generating the HBr in situ (NaBr + H2SO4 –> NaHSO4 + HBr)
Then:
CH3CH2CH2(OH) +HBR –> CH3CH2CH2BR +H2O
