Module 4.2 - Alcohols, Haloalkanes and Analysis Flashcards
What is the general formula of an alcohol?
CnH2n+1OH
What 3 groups can alcohols be classified into?
- primary alcohol
- secondary alcohol
- tertiary alcohol
What is a primary alcohol?
- has the functional group attached to a carbon atom with no more than one alkyl group
- OH at t6he end of a chain
What is a secondary alcohol?
-has the functional group attached to a carbon atom with two alkyl chains (+one H)
What is a tertiary alcohol?
-has the functional group attached to a carbon atom with 3 alkyl groups
Describe the trend in boiling points of alcohols of increasing chain length.
- increases as chain length increases
- as molecules get longer more areas of surface contact
- stronger/more London forces
- more energy needed to overcome these attractive forces
Compare the boiling points of alcohols with their corresponding alkanes.
- higher than alkanes
- H bonds between alcohol molecules
- H bonds stronger than London forces
- more energy needed to overcome H bonds than London forces
What does it mean if a substance is volatile?
- evaporates easily at room temp/pressure
- volatility increases as boiling point decreases
Compare the volatility of alcohols and their corresponding alkanes.
alcohols have H bonds so are less volatile than corresponding alkane
Describe the solubility of alcohols and the trends in solubility as chain length increases.
- water molecules are polar + so is the alcohol functional group
- methanol/ethanol/propanol are soluble in water as molecules form H bonds w molecules (sometimes described as miscibility)
- as alkyl chain length increases solubility of alcohol decreases because aliphatic chain can’t form H bonds + this become the larger part of the molecule
When would alcohols be combusted?
- used as fuels
- combustion transfers stored chemical energy to a usable form e.g. thermal energy
What are the products of the complete combustion of an alcohol? What is the equation for the complete combustion of ethanol?
- carbon dioxide and water
- C2H5OH(l) + 3O2(g) –> 2CO2(g) + 3H2O(l)
What is formed under gentle heating (distillation) of a primary alcohol and what colour change of the acidified potassium dichromate occurs?
- aldehyde
- orange to green
What is formed under the stronger heating (reflux) of a primary alcohol (in excess acidified potassium dichromate) and what colour change of the acidified potassium dichromate occurs?
- carboxylic acid
- orange to green
What is formed when a secondary alcohol is heated under reflux and what colour change of the potassium dichromate occurs?
- ketone
- orange to green
What is formed when a tertiary alcohol is heated under reflux and what colour change of the potassium dichromate occurs?
- no reaction
- remains orange
What are oxidising agents simplified to in equations?
[O]
What is the equation for the distillation of propan-1-ol?
C3H7OH + [O] –(K2Cr2O7/H2SO4)–> C2H5CHO + H2O
propan-1-ol + [O] –> propanal + water
What is the equation for the reflux of proan-1-ol?
C3H7OH + 2[O] –(K2Cr2O7/H2SO4)–> C2H5COOH + H2O
propan-1-ol + 2[O] –> propanoic acid + water
What is the equation for the reflux of butan-2-ol?
CH3CHOHCH2CH3 + [O] –(K2Cr2O7/H2SO4)–> CH3CoCH2CH3 + H2O
butan-2-ol + [O] –> butanone + water
Describe how an alcohol would be dehydrated.
- water is lost from the organic compound (eliminated)
- heated with strong acid (e.g. conc H2SO4) water is eliminated making an alkene
- -OH group from one C atom + H atom on adjacent C atom are lost to form a water molecule
- pi bonds between the 2 adjacent C atoms
What is the general equation for a halide substitution to an alcohol?
HX + ROH –> RX + H2O
Describe halide substitution to alcohols?
- halide takes place of -OH forming a haloalkane
- reagent is a hydrogen halide
- conc acid catalyst + warmed to increase rate of reaction
- when iodide uses H3PO4 used as H2SO4 oxidises iodide ions to iodine so yield of desired iodialkane is v low
What causes haloalkanes to react?
- polar as large difference in electronegativity between C-X
- electrons in C-X bond spend more time at X so delta charges form
- carbon atom attacked by atoms/molecules/ions with partial/full -ve charge. These species called nucleophiles
