Notesale: Turn your study into money

Document Preview

Extracts from the notes are below, to see the PDF you'll receive please use the links above

---

Optical Isomers
All molecules have a mirror image, for most it is the same molecule but for some the mirror
is a different molecule i
...
the mirror image is non-superimposable
...
These molecules are said to be chiral or optically active
...


Polarimeters are used to analyse the effect optical isomers have on plane polarised light
...

Chiral molecules react differently with other chiral molecules as the molecule must be the
correct shape to that of the molecule which it is reacting with
...
Amino acids are chiral along with amny other molecules, but naturally only one optical
isomer occurs (All natural amino acids are polarised to the left)
Many drugs are optically active with one entantiomer having a positive, beneficial effect,
sometimes the other entanntimer can even be harmful
...

this led to many disabilities in babies and early deaths
...


Isomerism

Structural
Isomerism

Chain Isomerism

Position
Isomerism

Stereoisomerism

Functional
Group
Isomerism

Geometric
Isomerism

Optical
Isomerism

Structural Isomerism- Molecules with the same molecular formula but with different structures
Chain Isomerism- Have different carbon skeletons but the same molecular formula
Position isomerism- Same carbon skeleton and functional group but the functional group is located
on different positions of the molecule
Functional Group Isomerism- Compounds with the same molecular formula but different functional
groups and so have different chemical and physical properties
Stereoisomer- Molecules with same structural formula but their bonds are arranged differently in
space
Geometric Isomers- (Cis/trans isomers) Isomers result from different spatial arrangements of
functional groups relative to the double bond
...

Optical Group Isomers- Compounds whose molecules are alike in every other way, are mirror
images of each other with a chiral compound

Carbonyl Group Chemistry C=O
Aldehydes and ketones are formed by the oxidation of primary and secondary alcohols using
acidified KMnO4 or K2Cr2O7
...

Primary Alcohols + [O]  Aldehydes + H2O
Aldehydes + [O]  Carboxylic Acids
...
In order to isolate an aldehyde we must immediately distil it
from te reaction mixture before it can be oxidised further to the acid
...
Hence the [O] cannot
remove two hydrogen atoms to form water and the carbonyl group
...


Aldehydes and ketones can also be reduced
...

Reduction of an aldehyde (Ethanal)

Reduction of a ketone (Propanone)

Reduction of propanone

Propenal with hydrogen gas and Ni catalyst

Propenal with NaBH4/ H2SO4

Nucleophilic Addition Reactions
The C=O bond is highly polar due to the electronegative oxygen which causes the C to be
electron deficient, thus susceptible to nuclophiles which have lone pairs of electrons for bonding
...
Sulphuric acid is added as a source of H + ions
...
The reaction intermediate has an oxygen atom carrying a negative charge
...

KCN(aq) supplies :CN- nucleophile
H2SO4(aq) supplies H+
Room temperature and pressure

RCOR + HCN  RC(OH)(CN)R
RCHO + HCN  RCH(OH)CN
When butanone is mixed with HCN a racemic mixture forms because :CN - is planar so will attach on
two different planes causing there to be an equal amount of two entantiomers
...

Aldehyde/ Ketone Tests
Fehlings solution is a very weak oxidising agent which is blue and contains copper(II)
...
No reaction with ketone
...
Silver (I) complex ion
reduces to metallic silver (0) when warmed with aldehyde
...

RCOH + 2[Ag(NH3)2] + 2OH-  RCOOH + 2Ag(s) + 4NH3 + H2O
Oxidising Agent
K2Cr2O7/H+
Fehling’s Solution
Tollen’s Reagent

Priamry Alcohol

X
X

Secondary Alcohol

X
X

Tertiary Alcohol
X
X
X

Aldehyde




Ketone
X
X
X

Carboxylic Acids




Carboxylic acids are weak acids so only partially dissociate in water
Produce CO2 when they react with carbonates
Effervescence with a metal carbonate usually means that the unknown solution contains an
acid

Reactions of Carboxylic Acids
Metal + Carboxylic Acid  Salt + Hydrogen
M + RCOOHM(RCOO-) +H2
Metal Hydroxide + Carboxylic Acid  Salt + Water
M+OH- + RCOOH  M(RCOO-) + H2O
Metal Carbonate + Carboxylic Acid  Salt + Water + Carbon Dioxide
MCO3 + RCOOH  M(RCOO-) + H2O + CO2
Carboxylic Acid + Water  ~ate ion + Hydroxonium ion
RCOOH + H2O  RCOO- + H3O+

Esters
An ester is formed when a carboxylic acid reacts with an alcohol in the presence of a
concentrated, strong acid catalyst (E
...
Sulphuric acid, concentrated Hydrochloric acid)
...


Radioactive labelling shows that the C-O bond on the carboxylic acid is more likely to break
rather than the C-O bond on the alcohol
...
Yields can be increased by
using acid chloride or acid anhydride instead of carboxylic acid called acylation reactions
...
In
order to test for a carboxylic acid or alcohol we can use the other in an acidic solution in order to
produce a fruity smell, as the vinegar like smell will be removed
...

Ester
Flavour
Ethyl methanoate
Raspberry
Ethyl butanoate
Pineapple
Ethyl ethanoate
Pear drops
2- Pentyl ethanoate
Pear

Esters can also be used as plasticisers which are additives to the polymer to increase
flexibility
...
PVC consists of very long polymer
chains
...

Plasticiser molecules penetrate between the chains and increase the distance between
them
...

Immitation leather is made using PVC and plasticiser but over time the ester evaporates so
the leather becomes cracked as it loses flexibility
...
They just have dipole- dipole bonds compared to carboxylic acids and alcohols which have
intermolecular hydrogen bonds
...
This accounts for their scent- they are more volatile so can reach our noses faster
...

Hydrolysis
Hydrolysis is the reverse of esterfication
...
Heat is required along
with concentrated sulphuric acid with addition of excess sodium hydroxide to form a salt
...
The
fatty acids are derived from natural fats and oils tri-esters of the trihydric (containing 3 –OH groups)
alcohol propane- 1,2,3, triol (glycerol) and three fatty acids
...
After boiling, salt is added to precipitate the
soap
...
Whenever soaps are manufactured glycerol is used in a wide range of
industries such as pharmaceuticals and cosmetics
...
The long hydrocarbon chains are attracted to oil as they are
hydrophobic
...
The H+ ions replace the Na+ ions
...

Tri-ester + Sodium Hydroxide  Glycerol + Sodium Stearate

An ester name has two parts;
-Prefix from the alcohol
-Suffix from the carboxylic acid
(Alcohol)~yl (Acid)~anoate

Biodiesel and Bio-fuels
Biodiesel is used in normal diesel engines and made from vegetable oils such as rapeseed
oil, sunflower oil and soybean oil as well as animal fat
...
Biodiesel is carbon neutral and therefore completely
sustainable, causing less pollution
...

Biodiesel is produced by transesterfication where the triglyceride ester, which gives a thicker oil is
converted to the less viscous methanol-based ester using sodium hydroxide catalyst
...


There is an issue involving oil- rich products or sugar cane which can be fermented to ethanol,
because this method of landuse may be in competition with food crops
...

2) Carbon neutral- Carbon is neither taken from or released into the atmosphere as an overall
effect when biofuels are used
...
Carbon dioxide is associated with global warming and climate change
...
Finally particulates cause asthma
...

5) The esters are highly volatile
6) Hydrolysis
7) First generation biofuels could be biodiesel which has been derived from plants (recently
dead matter) while second generation biodiesel could be from dead matter such as wood
chip
8) Second generation biodiesels are advantageous as they do not use land which is required for
food crops and some materials (e
...
wood) can be recycled

---