Alcohols - Organic Chem I Flashcards
What are alcohols governed by? Why are they present?
Strongest type of intermolecular force present: hydrogen bonds
Because the -OH group contains the two essential features needed: a hydrogen atom directly attached to a highly electronegative oxygen atom
Why do alcohols have a higher mpt/bpt than alkanes of similar Mr value?
More energy is needed to overcome the London forces, diploe-dipole forces and hydrogen bonds between alcohol molecules than just the weak London forces between alkane molecules
Why are alcohols (with short hydrocarbon chains) miscible with water?
Alcohols can form hydrogen bonds with molecules
Why do diols, and particularly triols, have relatively high viscosity?
The greater the number of OH groups per molecule the stronger the hydrogen bond
Show what the combustion of alcohol would look like?
Alcohols burn with a clean flame (implies complete combustion)
Eg/ CH3CH2CH2OH + 9/2O2 → 3CO2 + 4H2O
What is the reagent, condition and product of the chlorination of alcohol?
Reagent: PCl5
Conditions: room temp
Product: chloroalkane
What is the reagent, condition and product of the bromination of alcohol?
Reagent: KBr + 50% H2SO4
Conditions: heat under reflux
Product: bromoalkane
What is the reagent, condition and product of the iodination of alcohol?
Reagent: I2 + moist red phosphorous
Conditions: warm
Product: iodoalkane
What’s the test for alcohols?
Test: add a small amount of PCl5 to the substance
Result: if an alcohol is present steamy fumes are observed which turn damp blue litmus paper red (as HCl gas is produced)
What is the equation of an alcohol reacting with PCl5?
ROH + PCl5 → RCl + POCl3 + HCl
Eg/ CH3CH2OH + PCl5 → CH3CH2Cl + POCl3 + HCl
What does a dehydration reaction look like?
Removes H2O from an organic compound (alkene + H2O)
Reagents and conditions: conc H3PO4 (warm)
What is the commonly use oxidising agent?
Potassium dichromate (VI) (K2Cr2O7) in dilute sulfuric acid
Half equation for the reduction for Cr2O7 and give the colour change?
Cr2O7^2- + 14H+ + 6e- → 2Cr^3+ + 7H2O
Orange → green
What is the alternative oxidising agent and give the half equation for that:
Potassium manganate (VII) in dilute sulphuric acid
MnO4- + 8H+ + 5e- → Mn2+ 4H2O
Purple → colourless
What are primary alcohols oxidised to? Give the conditions
Primary alcohols are partially oxidised to aldehydes (by distillation) and fully oxidised to carboxylic acids (by heating under reflux) . Using potassium dichromate (VI) in dil. H2SO4
Why is this reaction carried out in distillation apparatus?
Because the desired product, the aldehyde, has a lower boiling point than the primary alcohol. This means that as soon as the aldehyde forms it distils over preventing it from being further oxidised to the carboxylic acid. The primary alcohol remains in the flask, allowing more aldehyde to form
Why does the aldehyde have a lower boiling point than the alcohol?
Aldehydes cannot form hydrogen bonds
Therefore less energy will be needed to overcome the London forces and dipole-dipole
What does the oxidation of secondary alcohol look like?
Secondary alcohols are oxidised to ketones. Same oxidising agent is used and the mixture has to be heated under reflux
What does heating under reflux allow you to do for a prolonged amount of time?
Heat a reaction for a prolonged amount of time without losing any reactants or products.
What happens after the reaction mixture is heated?
The reaction mixture boils and the vapours travel up to the condenser, where they condense and drop back into the flask.
How can the rate of boiling be controlled?
Using anti-bumping granules as well as monitoring the heat source.
- They encourage small bubbles to form and therefore smooth boiling
Why does the water have to enter the condenser at the bottom?
So it flows through the water jacket against gravity to avoid any air bubbles. Ensures all of the condenser is cooled
What are the two reasons in why you might want to use the distillation apparatus?
Can be used to obtain a pure product from a crude mixture. If the mixture contains only two or three components, then simple distillation apparatus can be used.
What is the method of separating two solvent and product?
Solvent extraction - relies on the desired product being more soluble in the added solvent than the reaction mixture.
What is observed when a drying agent is used?
The liquid should go from cloudy to clear (as the water is removed)
Name the 3 main drying agents:
Anhydrous MgSO4(s)
Anhydrous Na2SO4(s)
Anhydrous CaCl2(s)
What do you do to get rid of the drying agent?
The mixture is then filtered (decanted) to remove the drying agent
What does it mean when a compound burns with a clean flame
The compound is saturated