Topic 8: Introduction to Organic Chemistry
1. Formulae: Empirical, Molecular, Structural (condensed, displayed/full structural, skeletal),
Stereochemical
2. Aliphatic compounds: compounds with open chains of carbon atoms, may be branched or
unbranched, may contain single, double or triple bonds or combinations of these
3. Alicyclic compounds: compounds with closed rings of Carbon atoms
4. Aromatic compounds: compounds containing at least one aromatic system such as a benzene
ring
Hierarchy of suffix
Functional Group
Prefix name
Suffix name
Structure
naming
Highest priority
Carboxylic acid
-oic acid
O
R - C - OH
Ester
-oate
O
R – C – OR’
Acid halide
-oyl halide
O
R–C–X
Amide
-amide
H
R–N
H
Nitrile
Cyano-
-nitrile
Aldehyde
Formyl-
-al
R–CΞN
O
R–C–H
Ketone
Oxo-
-one
O
R – C – R’
Alcohol
Hydroxyl-
-ol
Amine
Amino
-amine
R–O–H
O
R – C – N – R’
Lowest priority
H
Alkene
-ene
R – C = C –R’
5. Addition: reaction between 2 molecules to form a single molecule. An unsaturated functional
group is usually involved
6. Substitution: when one atom or group of atoms is substituted by another. There are always at
least 2 product
7. Elimination: formation of an unsaturated compound with the elimination of a small molecule
8. Oxidation: a reaction in which at least one oxygen atom is added to the molecule or hydrogen
atoms removed from the molecule
9. Reduction: a reaction in which oxygen atoms are removed from the molecule or hydrogen
atoms are added to the molecule
10. Condensation: the expulsion of a small molecule when 2 molecules come together to form a
bigger molecule
11. Hydrolysis: a reaction in which a molecule is split into 2 by the action of water, often
catalysed by dilute acids/alkalis
12. Homolysis: aka homolytic fission, involves splitting of a single bond resulting in equal sharing
of the bonding electrons to each resultant particle – results in the formation of radicals
13. Heterolysis: aka heterolytic fission, involves splitting of a bond resulting in unequal sharing of
the bonding electrons to each resultant fragment – results in the formation of ions
14. Electrophile: electron-deficient/electron-seeking reagents that can develop an electron
deficient centre
15. Nucleophile: electron-rich/nucleus-seeking reagents
16. Reaction Intermediates: species that are formed in one of the steps of the reaction
mechanism and are consumed in later steps
17. Free radicals: electrically neutral atom/groups of atoms that has an unpaired electron
18. Carbocation (Carbonium ion): a species that contains a Carbon atom bearing a positive charge
– strong electrophile
19. Carbanion: a species that contains a Carbon atom bearing a negative charge – strong
nucleophile
20. Isomers: structures having the same molecular formula but having different arrangements of
the atoms
21. Structural isomerism: substances with the same molecular formula but different structural
formula – functional group/positional/chain
22. Stereoisomerism: substances with the same attachment of atoms to each other, but different
spatial arrangement – geometric/optical
23. Optical activity: ability of a compound to rotate the plane of polarised light
Topic 9: Alkanes
Mechanism of Free Radical Substitution
Stage 1: Initiation
Cl – Cl
UV
2Cl
Stage 2: Propagation
Cl
+ CH4
HCl + CH3
Stage 3: Termination
Cl + Cl
Cl2
Cl
CH3Cl
+ CH3
CH3 +
CH3
CH3 CH3
CH3 + Cl2
CH3Cl + Cl
𝑦
𝑦
24. Equation of Combustion: CxHy + (x + 4)O2
xCO2 + 2H2O
25. Cracking: a process in which C – C bonds in long-chain alkane molecules are broken to
produce smaller molecules of alkanes and alkenes
26. Thermal cracking:
a. Criterion: heat with steam at 800oC, moderate pressure, in absence of air
b. Proceeds by free radical mechanism
c. Very little rearrangement of the chains
27. Catalytic cracking:
a. Criterion: 500oC, slight pressure, passed over Al2O3 & SiO2
b. involves formation of carbocations which can undergo internal rearrangement
before forming the final products
28. Catalytic Reforming: chanese straight-chain alkanes into branched-chain alkanes and cyclic
hydrocarbons without the loss of any carbon atoms, but often with the loss of hydrogen
atoms
Topic 10: Alkenes
1. Alkenes: unsaturated hydrocarbons that contain at least one carbon-carbon double bond
Mechanism of Electrophilic Addition
Stage 1: Rate-determining step
H
H
C=C
H
δH – Br
H
δ+
H
H
H–C–C+
H
+
Br
H
Stage 2: Fast Step
H
H
H–C–C+
H
H Br
Br
H–C–C–H
H
H H
* In an electrophlic addition to an alkene, the electrophile adds in such a way so as to generate
the most stable carbocation intermediate
2. Markovnikov’s Rule: in the addition of HX to an alkene, the H atom adds to the C atom of the
double bond that already has the greater number of H atoms directly attached
Mechanism of Electrophilic Addition of Halogens
Stage 1: Rate determining step
H
H
C=C
H
δBr – Br
H
δ+
H
H
H–C–C–H +
Br+
Br
Stage 2: Fast Step
H
H
H H
H–C–C–H
Br
H–C–C–H
Br+
Br Br
Criterion: absence of light, liquid Br, room temperature
3. Hydration:
a.
Industrial Conditions: Phosphoric acid H3PO4 catalyst, 300oC, 70 atm
b.
Lab Conditions: conc. H2SO4, room temperature, warm with water
c.
Alkene -> Alcohol
4. Hydrogenation:
5.
a.
Conditions: Hydrogen gas, Ni/Pd/Pt catalyst, high temperature, high pressure
b.
Alkene -> Alkane
Mild Oxidation:
a.
Conditions: KMnO4, NaOH, cold
b.
Observations: purple KMnO4 is decolourised and a brown precipitate of MnO2 is
formed
c.
6.
Alkene -> Alcohol
Oxidative Cleavage
a.
Conditions: conc. KMnO4, dilute H2SO4, heat
b.
Observations: purple KMnO4 is decolourised
c.
Alkanes with terminal double bonds (=CH2) would, upon oxidation, evolve CO2 and
H2O
Topic 11: Arenes
1. Huckel’s Rule: estimates whether a planar ring will exhibit aromatic properties
a. 4n + 2 electrons in the delocalised p-orbital cloud
b. Planar and cyclic
c. Every atom in the circle is able to participate in delocalising the electron cloud by
having a p-orbital or an unshared pair of electrons
2. Order of precedence as principal functional group: -CO2H > -OH > -CH3 > -halogen > -NO2
Reactions of Benzene
Mechanism
Conditions & Observations
Reagents
Note
Stages
Nitration
Conc. HNO3, Yellow oil
conc. H2SO4, (nitroheat at 55oC benzene)
formed
Above 100oC, 1: Generation of electrophile
HNO3 + 2H2SO4
NO2+ + 2HSO4- + H3O+
further
nitration will 2: Attack by electrophile to form
occur to give carbocation intermediate (slow step)
H NO2
1,3,5+ NO2+
nitrobenzene
(carbocation)
3: Extraction of proton by base HSO4- to
restore stable delocalised π system and
regeneration of catalyst
O2N H
NO2
+ HSO4-
Halogenation Br2(l),
+ H2SO4
Decolourisa-
Lewis acid
1: Generation of electrophile
anhydrous
tion of
catalysts
FeBr3 + Br2
FeBr3/AlBr3
reddish-brown are required
as catalyst,
Br2(l),
to generate
warm
formation of
the strong
dense white
electrophile
fumes of HBr,
Br+
FeBr4- + Br+
2: Attack by electrophile to form
carbocation intermediate (slow step)
H Br
+
Br+
(carbocation)
chloro3: Extraction of proton by base HSO4- to
restore stable delocalised π system and
regeneration of catalyst
Br H
Br
benzene
formed
+ FeBr4-
+ FeBr3 + HBr
Friedal-
CH3Cl/AlCl3
Methyl-
Not feasible
Crafts
as catalyst,
benzene is
for longer
1: Generation of electrophile
CH3Cl + AlCl3
CH3+ + AlCl4-
alkylation
warm
formed
alkyl
2: Electrophilic attack to form carbocation
(not in
syllabus)
H CH3
substituent
due to
+ CH3
+
(carbocation)
occurrence
of 1,2hydride
shift that
results in a
more stable
carbocation
3: Extraction of proton by AlCl4- to restore
stable delocalised π system and regenerate
catalyst
H3C H
CH3
+ AlCl4-
+ AlCl3 + HCl
3. Activating groups: Electron-donating substituent that increases the electron density of the
benzene ring, thereby increasing the reactivity of the benzene ring
4. Deactivating groups: Electron-withdrawing substituent that decrease the electron density of
the benzene ring, thereby decreasing the reactivity of the benzene ring
5. Through the sigma bond – Inductive effect
Present when there is a difference in electronegativity between the bonding atoms
6. Through the pi bond – Resonance effect
Present when there is overlapping of p-orbitals
Substituent
Inductive
Resonance
Overall effect
Effect on position of
effect
effect
on reactivity
incoming electrophile attack
Alkyl groups eg.
Electron-
CH3
donating
Polar –OH, -NH2, Electron-
Activating
2, 4-directing
Deactivating
2, 4-directing
Electron-
-OCH3
withdrawing donating
Halogens –Cl,
Electron-
-Br
withdrawing donating
Electron-
Contain polar
Electron-
multiple bonds
withdrawing
3- directing
eg. –CHO, -NO2
7.
Activating groups and halogens are 2, 4-directing
8.
Deactivating groups are 3-directing
Reaction
Conditions & Observations Note
Stages
Reagents
Ring
Conc. HNO3, 2-nitromethyl Above 30oC,
reaction:
conc. H2SO4, benzene and
Nitration
heat at 30oC 4-nitromethyl is possible
benzene are
major
products
1: Generation of electrophile
NO2+ + 2HSO4- + H3O+
disubstitution HNO3 + 2H2SO4
2: Attack by electrophile to form
carbocation intermediate (slow step)
and 2, 4CH3
CH3
dinitromethyl
H NO
+ NO2+
2
benzene is
(carbocation)
produced
CH3
CH3
Further
+ NO2+
heating to
(carbocation)
110oC leads
H NO2
to formation
of 2, 4, 6-trini 3: Extraction of proton by base HSO4- to
tromethylben restore stable delocalised π system and
regeneration of catalyst
zene (TNT)
CH3 H
CH3
NO2
NO2
+ HSO4
+ H2SO4
CH3
CH3
+ HSO4-
+ H2SO4
O2N H
Ring
Br2(l),
Decolourisa-
Lewis acid
reaction:
anhydrous
tion of
catalysts are
reddish-
required to
as catalyst,
brown Br2(l),
generate
absence of
formation of
the strong
light, room
dense white
electrophile
Halogenation FeBr3/AlBr3
temperature fumes of HBr
Br+
Side-chain
Cl2(g), UV
More than
reaction:
light or heat yellow Cl2
Greenish-
one chlorine
Free radical
decolourises
atom can be
Substitution
slowly
incorporate
NO2
CH3
CH3
CH3
+ Br2
Br +
Br
CH3
CH2Cl + HCl
if excess Cl2
is used
Side-chain
KMnO4,
Purple
Benzoic acid
reaction:
dilute
KMnO4 is
is always
Oxidation
H2SO4, heat
decolourised
formed
and white
regardless
precipitate of
of the
benzoic acid
length of
is formed
the alkyl
+HBr
CH2CH2CH3 + 5[O]
COOH + CH3COOH +H2O
CH2CH3 + 6[O]
side chain
COOH + CO2 + 2H2O
CH3
CHCH3 + 9[O]
COOH + 2CO2 + 3H2O