Alchohols Flashcards
General formula of alcohol
CnH2n+1OH
What is a primary alcohol
The -OH group is attached to a carbon that has 1 other carbon attatched to it
Secondary alcohol
The -OH group is attached to a carbon that has 2 other carbons attatched to it
Tertiary alcohol
The -OH group is attached to a carbon that has 3 carbons attatched to it
Are alcohols polar
Alcohols are generally polar molecules due to the the electronegative hydroxyl group which pulls the electrons in the C-OH bond away from the carbon atom
This means the electronegative oxygen draws electron density away from hydrogen , giving it a slightly positive charge - can attract lone pairs on an oxygen forming H bonds
Alcohol + water - smaller vs larger alcohols
When you mix an alcohol with water, hydrogen bonds form between the oh- and h20
smaller - completely soluble
Larger - most of the molecule is non polar carbon chain, so there’s less attraction for the polar h20 molecules - less soluble in water
Why do alcohols have low volatility ( don’t easily evaporate into a gas)
Alcohols form H bonding with EACH THER
HYdrogen bonding is the strongest type of intermolecular force, so it gives alcohols LOW volatility
ALchohols vs alkanes
Alkanes have non polar bonds because electronegativity of C and H is too similar
Intermolecular forces = weak London forces
High volatility = low BP, not much energy required to break London dispersion
Non polar too- can’t form H bonds with each other
Reactions of alcohols
Combustion
Oxidation
Dehydrating
Forming halo alkanes
Combustion of alcohols
Burn completely in O2 (plentiful supply) to form h20 and co2
EXOTHERMIC reaction , releasing a lot of energy
As the number of C atoms in the chain increases, the au titis of heat released per mole also increases
C-C and C-H bonds broken
Oxidation of primary alcohols
Partial oxidation
ALDEHYDE
Potassium dichromate solution+dilute sulphuric acid
Distil out aldehyde once formed
Colour change ? Oxidation for primary alcohol.s
Dichromate changes colour from Orange to green ( Cr3+)
Full oxidation of primary alcohols
CARBOXYLIC acid
Heat under reflux
Secondary alcohol oxidation
Refluxing a secondary alcohol with acidified dichromate will reduce a KETONE and water
Again orange to green
alchohol + [o]—- ketone and water
Tertiary alcohol oxidation
DO NOT react with dichromate - solution stays orange
Cannot be oxidised
No hydrogen atom bonded to carbon with OH group for the oxygen to remove
Dehydrating alcohols
ALKENES
Eliminate H20
Eliminatin reaction
Alcohol mixed with acid catalyst e.g. H2so4, then heated
Water bonded to carbon atom adjacent to hyxxul carbon
Halo alkanes from alcohols
HYDROGEN HALIDES Heat under reflux Sulphuric aci and halide ions Hydroxyl group replaced by halide Neucleophlic substitution
