Alcohols Flashcards
refresher on naming alcohols
OH functional group
named using suffix of ol
longest C chain containing OH group is stem
name giving OH group lowest number
remember no constantans next to each other
if more than 1 hydroxyl group then E not dropped
if 2 suffixes use prefix hydroxyl
solubility of alcohols
alcohols dissolve in water as polar OH group forms H bonds with polar H2O molecules
first 3 members of homologous series are all soluble in water
sol decreases as chain length increases
as larger part of molecule made up of non polar HC chain
HC chain doesn’t form H bonds with H2O molecules
volatility/ bp of alcohols
higher bps than Alkanes
H bonds between molecoules
need a sig amount of energy to overcome
require more energy than IDD forces in alkanes
so alcohols have lower volatility and higher bp than alkanes with same C chain length
Bp increases as chain length increases
more surface contact and electrons
more H bonds
more energy needed to overcome
classifying alchols
Primary- OH group is attached to carbon with only 1 alkyl group
e.g.
H H
H-C-C-OH
H H
Secondary- OH group is attached to C with 2 alkyl groups
e.g.
H OH H
H C–C–C H
H H H
tertiary- OH group is attached to a C with 3 alkyl groups
e.g.
H CH3 H
H C–C–C H
H OH H
Combustion of alcohol
in plentiful O2 alcohols burn completely to give CO2 and Water
e.g.
CH3CH2CH2OH + 4.5O2 -> 3CO2 + 4H2O
Dehydration- elimination of H20 from an alcohol
When a H20 molecule is removed from a saturated compound to form an unsaturated molecule
reagent: Conc H3PO4/ H2SO4 catalyst and alcohol
conditions: Heat under reflux (look at map for diagram)
OH is removed from 1 carbon and a H atom is removed from adjacent Carbon
H H H H H C C OH ---> C=C + H2O H H H H
forms alkene
Some can’t be dehydrated e.g. if the C attached to OH is attached to a C with no carbon atoms
Oxidation of alcohols basic knowledge
P and S can be oxidised using oxidizing agent
T cannot
suitable Oxidizing agent is solution containing acidified dichromate (Cr2O7 2-/H+)
symbol of oxidised agent in balanced equation is [O]
[O] change colour orange—>green
Partial Oxidation + further of P alcohol
Reagent - Acidified dichromate (H2SO4 and K2Cr2O7)
condition: heat by distillation
e.g.
OH O
R C H + [O] —> R C + H2O
H H
heated under distillation so that aldehyde is separated from reaction mixture to prevent further oxidation to carboxylic acid
Acidified dichromate solution added gradually via a tap funneling partially oxidised P alchol in flask
as soon as A forms is boils off as lowest BP (cont form H bonds)
Hot A vapour is cooled and condensed to liquid
Further Oxidation:
aldehyde easily oxidised further to a carboxylic acid
e.g.
O O
R C + [O] —> R C
H OH
Complete oxidation of P alchol
Reagent: Acidified dichromate e.g. H2SO4 and K2Cr2O7
condition: heat under reflux
completely oxidised to carboxylic acid
Acidified dichromate solution has completely oxidised the P Alcohol in flask to carboxylic acid
oxidation of secondary alcohol
Oxidised to Ketone
reagent: Acidified dichromate “
condition: heat under reflux
H OH H H O H
H C C C H + [O] —>H C C C H + H2O
H H H H H H
Low BP + not volatile
No H attached to C with O attached so can’t be oxidised further
Oxidation of Tertiary alcohols
Cannot be oxidised at all
as Teritary alcohols don’t have H atom on C which the OH is attached to
Nucleophilic substitution
alcohol+hydrogen halide—> haloalkanes
reagent: NaBr and conc H2SO4 (HBr is made in situ)
Conditions: Heat under reflux
NaBr(s) + H2SO4(aq) –> NaHSO4 (aq) + HBr(aq)
HBr formed the reacts with alcohol
Alcohol + HBr —> Haloalkane + H2O
Overall equation: Alcohol + NaBr + H2SO4 —> Haloalkane + NaHSO4 + H2O
