1. Topic 10 – Organic Chemistry
Section 10.2
Functional Group
Chemistry 1

2. Why Do Hydrocarbons Make Good Fuels?
To do:
Use Table 12 in the data booklet to help you determine the trend in energy released per gram by combustion of the alkanes.
Use bond enthalpies to help you explain the trend noted above.
What do you think should be the characteristics of a good fuel?
Use the above to decide and explain which out of methane and octane is a better fuel. 2

3. Functional Group Chemistry
Alkanes
relatively inert
used as fuel – easily combust with O2 and release a lot of energy
lower volatility as the carbon chain gets longer
alkane + O2 → CO2 + H2O
Complete combustion:
alkane + oxygen  carbon dioxide + water
Incomplete combustion:
Alkane + oxygen  carbon + carbon monoxide + carbon dioxide + water
The amounts of C, CO and CO2 will vary depending on conditions 3

4. Types of Reactions Substitution Oxidation Addition Elimination
Free radical substitution
Nucleophilic substitution
Electrophilic substitution
Oxidation
Combustion
Redox
Addition
Elimination 4

5. Classifying Molecules
Halogenoalkanes – look at the carbon attached to the halogen and see how many carbons it’s attached to.
Alcohols – same as halogens
Amines – how many carbons are directly bonded to the nitrogen 5

6. Halogenation
Alkanes are relatively stable and difficult to react, but will undergo halogenation if reacted with a halide in the presence of u.v. light.
For example:
C2H6(g) + Cl2(g) CH3CH2Cl(g) + HCl(g)
ethane chloroethane
This reaction is an example of free radical substitution. 6

7. Free Radicals
Free radicals are species with unpaired electrons formed by homolytic fission.
They are crazy reactive
Halogens form radicals when hit by uv light of the right frequency:
Cl Cl•
The dot after the Cl represents the unpaired electron and tells us we have a radical
Homolytic fission – the bond breaks equally with one electron going to each chlorine
Task: draw Lewis structures for the Cl2 molecule and each of the Cl• radicals
u.v. 7

8. Reaction Mechanism: Free Radical Substitution
Cl Cl•
Cl• + C2H6 → C2H5• + HCl
C2H5• + Cl2 → C2H5Cl + Cl•
Cl• + Cl• → Cl2
Cl• + C2H5• → C2H5Cl
C2H5• + C2H5• → C4H10
Initiation
Radicals formed by homolytic fission
Propagation
These steps feed each other the radicals needed to continue
Termination
Any two radicals can combine to terminate the reaction
Concentration of radicals is low so this is a rare event
u.v.
A single radical can cause thousands of cycles of the propagation stage before it reaches termination
This same mechanism applies to all of the halogens
The alkane can be substituted multiple times, until every H has been replaced 8

9. Free Radical Substitution
Remember the role of free radical reactions in the depletion of the ozone layer
Initiation
CF2Cl2(g) → CF2Cl•(g) + Cl•(g)
Propagation
Cl•(g) + O3(g) → ClO•(g) + O2(g)
ClO•(g) + O3(g) → Cl•(g) + 2O2(g)
Termination
Overall 2O3(g) → 3O2(g) 9

10. Demo Place approx 1 cm3 of hexane into two test tubes
Add roughly 1 cm3 of bromine water to each and stopper them, then give them a good shake.
Leave one test-tube in the classroom but take the other outside and shake it in direct sunlight.
Record and explain all observations
Write equations showing the mechanism of the reaction
Draw full structural and skeletal formulas of at least 6 possible products, and name each one. 10

11. Key Points Alkanes are pretty unreactive
They release a lot of energy on combustion, and are easy to handle which makes them good fuels.
Undergo free radical substitution to form halogenoalkanes and a hydrogen halide in the presence of UV light. 11

12. Nucleophilic Substitution Reactions
Carbon is e‾ deficient, so is ripe for attack by a nucleophile
Example: KOH attacking C
Electrophilic Substitution
electrophile is something that needs e‾
happens with benzene 12

13. Nucleophilic Substitution
SN1
Weak nucleophile
Leaving group controls rate of reaction
Stereo-isomer configurations (>50% inversion; <50% retention)
Rate = k[R-X] C X ••
Nu / Solvent Nu
Nu ̶ +
carbo-cation
X ̶
slow
fast 13

14. Nucleophilic Substitution
SN1
tert-carbon
more reactive
primary carbon
less reactive
Rule ̶ methyl < n ̶ < sec ̶ < tert ̶ C Cl ••
CH3 + C Cl •• H
CH3 + 14

15. Nucleophilic Substitution
SN2
Strong nucleophile
Always a primary carbon
Leaving group and nucleophile control rate of reaction
100% inversion isomer
Rate = k[R-X][Nu] C Nu C X •• ƍ + ƍ ̶ ••
X ̶
Nu / Solvent
Nu ̶ C X •• ƍ + 15

16. Oxidation Reactions Combustion Reactions Hydrocarbon + O2 → CO2 + H2O
Incomplete reaction
Products include C + CO + H2O 16

17. Chromate goes from 6+ (orange) to 3+ (green)
Oxidation Reactions
Alcohols
Using acidified K2Cr2O7 or KMnO4
Chromate goes from 6+ (orange) to 3+ (green)
Primary alcohol results in an aldehyde.
Secondary alcohol results in a ketone.
H ̶ C ̶ C ̶ C ̶ H H OH O →
H2SO4
K2Cr2O7 17

18. Oxidation of Alcohols → Alcohols Using acidified K2Cr2O7 or KMnO4
Primary alcohol – two-stage process that goes first to an aldehyde and then a carboxylic acid →
H ̶ C ̶ C ̶ OH H
H ̶ C ̶ C O
H2SO4
K2Cr2O7
H2SO4
K2Cr2O7
ethanol
ethanal
ethanoic acid 18

19. Oxidation Reactions Esterification → Using concentrated H2SO4
Carboxylic acid + alcohol → ester
conc. H2SO4 →
H ̶ C ̶ C ̶ C ̶ OH H O
H ̶ C ̶ C ̶ C ̶ O ̶ CH2CH3
+ CH3CH2OH 19

20. Functional Group Chemistry
Alkenes
Alkenes are considerably more reactive than alkanes and are a major industrial feedstock
The reactivity is due to the double bond:
The double bond contains 4 electrons
This is a significant amount of charge which:
Makes it attractive to electrophiles
Enables it to polarise approaching molecules
Most reactions of alkenes are addition reactions where two molecules come together to make one new one 20

21. Addition Reactions alkene + water → alcohol Reaction conditions:
Water must be steam
Phosphoric or sulphuric acid catalyst
This is the process used to make industrial ethanol
Fermentation from sugar would be far too expensive! 21

22. Addition Reactions alkene + hydrogen  alkane Reaction conditions: Hot
Ni catalyst
This is an addition reaction, in which the hydrogen adds across the double bond 22

23. Addition Reactions Alkene + hydrogen halide → halogenoalkane
Reaction conditions:
This reaction occurs very readily and needs no special conditions
This is an addition reaction, in which the hydrogen halide adds across the double bond 23

24. Addition Reactions + Br2 → C = C H H ̶ C ̶ C ̶ H Br
alkene + halogen → dihalogenoalkane
Reaction conditions:
This reaction occurs very readily and needs no special conditions
If the halogen used is an aqueous solution of bromine (bromine water), the orange-brown colour of bromine solution is decolourised.
This is the standard test for alkenes.
C = C H
+ Br2 →
H ̶ C ̶ C ̶ H Br 24

25. Homework Design and construct a functional groups table (landscape)
You need to research and produce a mind-map summarising the following functional groups:
Alkane
Alkene
Alcohol
Aldehyde
Ketone
Carboxylic acid
Ester
Halide/Halogenoalkane
Your table should have six columns including:
Name of functional group
General structural formula (use ‘R’ to signify a carbon chain)
Rules for naming them (including the position where relevant)
A named example
Relative volatility
Relative solubility in water
For alcohols and halides you should include a branch to explain the difference between 1o, 2o, and 3o
You should also have a branch called ‘Other Functional Groups’ that just allows you to recognise the groups:
Amine
Benzene 25

26. Functional Group Chemistry
Polymerization
Reactions of many small monomers with double bonds to form long chains
CH2 = CH
CH3 →
̶ CH2 ̶ CH ̶
CH n 26

27. Polymerisation
Under the right conditions, alkene molecules will add to each other creating a polymer
In this case, 1-bromo-2-fluoroethene polymerises to form poly-1-bromo-2-fluroethene
Conditions:
Vary from alkene to alkene, but often include high pressure, temperature and a catalyst
The carbons in the C=C double bonds form the carbon chain, everything else hangs off this chain 27

28. Drawing Polymers Draw three-monomer lengths of the polymers formed by:
Propene
Styrene
Pent-2-ene 28

29. Drawing Polymers Draw three-monomer lengths of the polymers formed by:
Propene
Solution:
Polypropylene
CH3 C H n 29

30. Drawing Polymers Draw three-monomer lengths of the polymers formed by:
Styrene
Solution:
Polystyrene C H
CH2
H2C n 30

31. Drawing Polymers Draw three-monomer lengths of the polymers formed by:
Pent-2-ene
Solution:
Polypropylene
CH2
CH3 C H n 31

32. Homework Research the economic importance of alkenes including:
Manufacture of margarine
Manufacture of ethanol
Polymerisation 32

33. SL Organic Pathways M KETONE ALKANE HALOGENOALKANE ALCOHOL ALDEHYDEUV +
Hal2
KETONE
ALKANE
Heat/UV M
Free Rad
Chain Rxn
HALOGENOALKANE
Warm
OH‾(aq)
Nucleophilic
Substitution
ALCOHOL
Heat
(Distill/Reflux) H+
K2Cr2O7/KMnO4
2º ALCOHOL
Heat (Distillation)
1º ALCOHOL
CARBOXYLIC ACID
ALDEHYDE
Heat (Reflux)
K2Cr2O7
TRIHALOGENOALKANE
TETRAHALOGENOALKANE
ALKENE
POLYALKANE
Heat, Pressure,
Catalyst
H-Hal/Hal2
H2 +
Hot Nickel
H2SO4
H3PO4 CATALYST
Al2O3
300ºC, 7 atm,
H2O
DIHALOGENOALKANE
+ Hal2
ALCOHOL ALKENE + H2O
ALKENE ALCOHOL - H2O
R-OH
conc. H2SO4
ESTER 33

34. Homework
Complete Kerboodle QUIZ on 10.2
Study for TEST 34