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- When two different substituents are present, number the ring by alphabetical
priority
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- When three and more substituents are present, begin at the substituent that
leads to the lowest set of location numbers
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EXERCISE 4:
Give the IUPAC name for the following structures:
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2.3 SOURCE OF ALKANE
1 The alkanes are isolated from natural gas and petroleum.
2 Natural gas contains mainly methane, with smaller amounts of other low‐
molecular‐weight alkanes.
3 Petroleum, which is a complex mixture of many compounds, is the main source
of all other alkanes. The lighter fractions are distilled from the mixture to produce
the liquid alkanes, while the residue from the distillation produces the solid
alkanes.
4 It is a complex mixture of compounds, most of which hydrocarbons containing
one to forty C atoms.
5 The constituents of crude oil are alkanes, some aromatics, and some undesirable
compounds containing sulphur and nitrogen.
6 A fossil fuel, petroleum is formed when large quantities of dead organisms,
mostly zooplankton and algae, are buried underneath sedimentary rock and
subjected to both intense heat and pressure. Petroleum has mostly been
recovered by oil drilling (natural petroleum springs are rare).
Petroleum crude oil “BLACK GOLD” Refinery plant
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gasoline: C5H12~ C12H26
kerosene: C12H26 ~ C16H34
diesel fuel: C15H32 ~ C18H38
Fractions from crude oil
2.4 PHYSICAL PROPERTIES OF ALKANES
1. Alkanes have densities between 0.6 and 0.8 g/cm3, so they are less dense
than water.
2. The gasoline, which is largely a mixture of alkanes, is less dense than water,
and will float on water.
3. Pure alkanes are colorless, tasteless, and nearly odorless.
4. Alkanes are not very reactive and have little biological activity.
Boiling Point of Alkane
Hydrocarbon Boiling Point (0C) Density (g/mL)
Heptane
98.4 0.6837
Octane 125.7 0.7025
Decane 150.8 0.7176
Cyclopropane -32.7 Gas at 200C
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1. Boiling point of alkanes increase smoothly with increasing number of C
atoms (molecular weight / molar mass).
2. Effect of increasing number of C atoms on boiling point:
- The greater the number of carbon atoms, the larger the molecule is.
- The molecule has bigger surface area in contact.
- The stronger Van der Waals attractive forces.
- More energy required to overcome the attractive forces.
- The higher the boiling point.
3. Effect of branching on boiling point:
- More branches, molecule become more compact.
- Surface area in contact are reduced.
- This causes the branched alkanes to have a weaker Van der Waals
attractive forces.
- Less energy required to overcome the attractive forces.
- The lower the boiling point.
4. Cyclic alkanes have higher boiling point than the corresponding straight chain.
This is because:
- Cyclic alkanes has larger surface area in contact than the corresponding
straight chain alkane.
- The stronger van der Waals attractive forces.
- More energy required to overcome the attractive forces
- The higher the boiling point.
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Solubility in Water and Organic Solvents.
1. Alkanes and cycloalkanes are almost totally insoluble in water because they
are:
(i) non-polar molecules
(ii) unable to form hydrogen bond with water (H2O) molecule.
2. Alkanes and cycloalkanes are generally dissolving in non-polar solvents.
Examples of non-polar solvent: benzene, chloroform, carbon tetrachloride, etc.
3. Reasons:
- Since alkanes are non-polar molecule, it cannot form hydrogen bond
with water molecule.
- Alkanes are soluble in non-polar solvent since it can form van der Waals
forces with the solvent molecule.
EXERCISE 1:
Arrange the following alkanes in order of increasing boiling points. Explain
1. methane, heptane, butane, octane.
2. hexane, 2,2- dimethylbutane, 3-methylpentane.
2.5 CHEMICAL PROPERTIES OF ALKANES
1. Alkanes are sometimes referred as paraffins.
2. They do not react with strong acids or bases or with most of other reagents
due to: Strong covalent bond of C–C and C–H
i. No lone pair or any functional group
ii.
3. They are two chemical reactions involve in alkane:
a. Combustion in three condition
i. Excess oxygen
ii. Limited oxygen
iii. Very limited oxygen
b. Free radical substitution reaction with halogen
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Combustion of Alkane
1. In excess oxygen
Reactant : alkane and excess O2
Product : CO2 and H2O
Large amount of heat is released
EXAMPLE:
EXERCISE:
Complete the following combustion reaction equations:
2. Combustion In Limited O2
Reactant : alkane and excess O2
Product : CO and H2O
EXAMPLE:
EXERCISE 1 :
Write a balance chemical equation for the combustion of CH3CH(CH3)CH(CH3)CH3
in :
(a) excess oxygen
(b) limited oxygen
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Halogenation
Reactants : alkane and halogen (X = Cl, Br)
Products : mixture of alkyl halides and hydrogen halide (HX)
Conditions : Light or heat
Type of reaction : Free Radical substitution reaction
Reactivity Of Halogen
- Br2 is less reactive than Cl2.
- Br2 is higher selectivity and giving the major product almost exclusively.
- The product form in monosubstitution product.
EXAMPLE:
*A molecule of alkanes in which only one hydrogen has been replaced by
another atom halogen (Cl/Br).
MECHANISM OF HALOGENATION
Overall reaction:
There are three steps of mechanism:
✔ Chain Initiation Step
✔ Chain Propagation Step
✔ Chain Termination Step
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STEP 1: CHAIN INITIATION STEP
- uv (ultraviolet) or sunlight or light or heat provides the energy needed for
homolytic cleavage
- Highly reactive radicals are produced
STEP 2: CHAIN PROPAGATION STEP
- One radical generates another.
STEP 3: CHAIN TERMINATION STEP
- A side reaction
- Two radicals combine
- No new radicals generated
- Chain reaction will slow or stop
EXERCISE 2:
Write the mechanism for chlorination of ethane to produce monochloroethane.
Prepared by: Revised by:
Nor Asmahan binti Abdullah Muhammad bin Seman
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1. Name the following compounds according to the IUPAC nomenclature:
(a). CH3CH2CH (CH3) CH2CH3 (b) CH3CH(CH3)CH(CH3)CH(CH3)CH2CH3
(c). (d).
(e).
2. Draw the structure for each of the following compounds:
(a) 3-methylpentane
(b) 3-ethyl-4,4-dimethylheptane
(c) 2,3-dimethylbutane
(d) 5-sec-butyl-2,4-dimethylnonane
(e) 3-cyclohexyl-2,2-dimethyl butane
(f) 4-isopropyl-1,1-dimethylcyclohexane
(g) cyclobutylcyclopentane
3. Arrange the following alkanes in the order of increasing boiling points. Explain your answer.
(a) CH3(CH2)3CH3, CH3CH2CH3, CH3(CH2)7CH3, CH3(CH2)5CH3
(b) pentane, 2-methylbutane, 2,2-dimethylpropane
(c) 2-methylbutane, 2,2-dimethylpropane, pentane, butane
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4. Explain why cyclohexane is insoluble in water but soluble only in benzene. Give another
example of the non-polar solvents.
5. (a) Explain why alkanes are generally unreactive.
(b) Write a balanced chemical equation for the combustion of hexane in
(i) excess oxygen
(ii) limited oxygen
6. A mixture of ethane and bromine is exposed to sunlight. The reaction equation is given
below.
CH3CH3 + Br2 ⎯⎯uv→ A
(a) State the type of the reaction above.
(b) What is the function of sunlight in the reaction?
(c) Draw the structure of the monosubstituted products, A.
(d) Write the mechanism for the formation of the product.
(e) Give the observation of the reaction.
(f) What would happen if the mixture is kept in the dark at room temperature?
7. An alkane has molecular structure CH4.
(a) Draw and name structures of the alkane.
(b) Name the isomer which form only one monosubstituted product
when react with chlorine in the presence of ultraviolet light.
8. Cycloalkane undergoes halogenation with bromine gas in the presence of sunlight.
(a) Write the equation for the above reaction
(b) What is the function of sunlight?
(c) Name the type of the reaction above.
(d) Explain the mechanism of the reaction.
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9. a) Draw all possible open-chain structures for the following molecular formula of
C5H12 and write their IUPAC name.
b) Write the equation for combustion of this molecule in excess oxygen and in limited
oxygen.
10. The fractions from petroleum contain alkane hydrocarbons.
(a) Write an equation for the incomplete combustion of the alkane C8H18 to
produce carbon monoxide and water only.
(b) One isomer of C8H18 is 2,2,3-trimethylpentane. Draw the structure of this
isomer.
11. Compound B is a saturated and symmetrical compound with a molecular
formula C5H12. Compound B gives only a single monobrominated product, C,
upon reaction with bromine gas in the presence of light. Write the structural
formulae of compounds B and C.
12. State the order of stages in the reaction between chlorine and methane in UV
light
13. Complete the statement regarding the boiling points of alkanes
a) Boiling point _________________ with stronger Van der Waal’s forces
b) Boiling point of straight chain alkanes is ____________ than that of branched
chain alkanes
14. If 25 mL of hexane were added to 100 mL of water in a beaker, what would you expect
to happen? Explain.
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OBJECTIVE QUESTIONS
1. The following compounds are alkanes EXCEPT
A. C5H12
B. C6H12
C. C7H8
D. C7H14
2. Which of the following reaction is a free radical substitution?
A. Hydrolysis of alkanes
B. Combustion of alkanes
C. Halogenation of alkanes
D. Hydrogenation of alkanes
3. Which of the following alkane has the lowest boiling point?
A. C5H10
B. (CH3)4C
C. (CH3)2CHCH2 CH3
D. CH3CH2CH2CH2CH3
4. Which of the following is a propagation step in the reaction between ethane and chlorine
A. Cl2 ⎯→ 2Cl•
B. •CH2CH3 + •Cl ⎯→ClCH2CH3
C •Cl + CH3CH3 ⎯→ •CH2CH3 + HCl
D •CH2CH3 + HCl ⎯→ CH3CH2Cl + H•
5. Ethane and bromine react in the presence of sunlight but not in the dark. Sunlight is needed
to initiate
A. the heterolytic fission of C-H bonds to form carbanion.
B. the homolytic fission of C-H bonds in ethane molecule.
C. the homolytic fission of Br-Br bonds in bromine molecule.
D. the heterolytic fission of bromine molecule to form bromide ions.
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6. In a free radical reaction, free radicals are formed at
A. initiation step
B. propagation step
C. termination step
D. both A and B
7. Formation of radicals which attack reactants molecules generate more free radicals. This
step is a____________________
A. initiation step
B. propagation step
C. termination step
D. elimination step
8. The first four alkyl groups respectively are
A. methyl, propyl, butyl and pentyl.
B. methyl, ethyl, propyl and butyl
C. ethyl, methyl, hexyl and butyl.
D. ethyl, propyl, butyl and heptyl.
9. Which one of the following substances is NOT considered to be an organic compound?
A. Octane
B. Carbon monoxide
C. Ethane
D. Methane
10. What is the correct IUPAC name for this alkyl group
-C4H9
A. propyl group
B. pentyl group
C. ethyl group
D. butyl group
Revised by:
Muhammad bin Seman
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CHAPTER 3: ALKENES
GENERAL OVERVIEW
3.1 Structure of a)Describe alkenes as unsaturated hydrocarbon
Alkenes with general formula CnH2n n≥2 (C2 - C10)
3.2 a) Draw the structures & name the i. straight chain (C2 - C10)
Nomenclature compounds according to the IUPAC ii. branched alkene
(C4 - C10)
3.3 Nomenclature for
Preparation iii. cyclic alkene (C4 -
a) Show preparation of alkene C6)
through dehyration of alcohols
b) State Saytzeff's Rule
c) Predict the major product using Saytzeff's Rule
(*exclude the mechanism)
i) H2 in the presence of catalyst
3.0 ALKENES ii) Halogen (Cl2 or Br2) in inert solvent
(CH2Cl2)
a) Explain addition
reaction of alkene with ii) Halogen (Cl2 or Br2) in water
iv) acid catalyst hydration
3.4 Reaction v) hydrogen halide (HCl or HBr)
vi) hydrogen bromide, HBr in the
presence of peroxide
b) Introduce Markovnikov's Rule for reaction a) v) and anti
Markovnikov's for reaction a) vi)
c) Write the mechanism for reaction a) v).
3.5 Unsaturation test a) Explain i. Baeyer's Test using
unsaturation test for dilute alkaline KMnO4
alkenes ii. reaction with bromine in CH2Cl2
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3.1 STRUCTURE OF ALKENES
✓ Alkenes are more reactive than alkanes
✓ General formula for alkene is CnH2n , n 2
✓ Functional group for alkene is carbon-carbon double bond (C=C). Thus alkene
is an unsaturated hydrocarbon.
✓ The simplest structure of alkene is ethene, CH2=CH2
3.2 NOMENCLATURE
✓ IUPAC names of alkenes have the -ene suffix.
Table 1: Naming for straight chain alkene (C2 – C10)
Molecular formula Structural formula Name
ethene
C2H4 CH2=CH2
C3H6 CH2=CHCH3 propene
C4H8 CH2=CHCH2CH3 1-butene
C5H10 CH2=CHCH2CH2CH3 1-pentene
C6H12 CH2=CH(CH2)3CH3 1-hexene
C7H14 CH2=CH(CH2)4CH3 1-heptene
C8H16 CH2=CH(CH2)5CH3 1-octene
C9H18 CH2=CH(CH2)6CH3 1-nonene
C10H20 CH2=CH(CH2)7CH3 1-decene
STEPS IN NAMING ALKENE COMPOUND
(FOR STRAIGHT AND BRANCHED ALKENE)
1. Find the longest C chain that contains both C atoms of the double bond.
2. Give the double bond the lower number. If double bond is at same distance from
the two ends, begin at the end nearer to the first branch point.
3. Name main chain using the first number assigned to the double bond.
4. Number the substituents according to their position in the chain, and list them
alphabetically
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CH
3
1 23 45 6
CH CHCH= CHCH CH
3 23
Name : 3-methyl-3 hexene
NAMING CYCLOALKENE
1. Number the cycloalkene so that the double bond is between C1 and C2 and the
first substituent has the lowest number possible
C1 C2
Name : 3-methylcyclohexene
CIS-TRANS ISOMER
HOW TO IDENTIFY CIS-TRANS ISOMER
✓ Have restricted rotation of carbon–carbon bonds due to the presence of carbon
double bond (C=C) or in cyclic structure.
✓ Have two different atoms or group of atoms attached to each of C atoms which
form double bond or cyclic structure.
✓ Cis isomer in alkene occur when two identical groups are attached on the same
side of the double bond.
✓ Trans isomer in alkene occur when two identical groups are attached on the
opposite side of the double bond.
✓ Example;
EXAMPLE 1:
Name the following compound.
a.
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b.
c.
Answer:
a. 2-hexene
b. 2-methyl-3-hexene
c. 3-methylcycloheptene
EXAMPLE 2:
Draw the structure corresponding to each name
a. 3,3–dimethylcyclopentene
b. cis-3-hexene
Answer:
a. b.
EXERCISE 1:
Name the following compound.
a.
b.
c. CH3CHClCH=CH2
d.
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EXERCISE 2:
Draw the following compound
a. 2,3,5-trimethyl-2-hexene
b. 1,5-dimethylcyclopentene
c. trans-2-pentene
EXERCISE 3:
Which of the following compounds can exist as cis–trans isomers?
For those compounds, draw and label (name) the cis and trans isomers?
a. CH3CH═CHCH2CH3
b. (CH3CH2)2C═CHCH3
c. CH3CH═CHCH3
d. CH3CH2CH═CH2
3.3 PREPARATION
DEHYDRATION OF ALCOHOL
✓ Dehydration of alcohol is one of the method to prepare alkene.
✓ Alcohols react with strong acids in the presence of heat to form alkenes and
water.
Reagent Conc.H2SO4 or Conc.H3PO4
Condition Heat H2SO4 (conc.) HH
General HH
equation
HCCH
+C C H2O
H OH HH
Type of reaction Elimination
✓ Concentrated sulphuric acid (H2SO4) or phosphoric acid (H3PO4) used as acidic
catalysts and dehydrating agents.
✓ The reaction involves elimination of H2O in which OH is removed meanwhile H is
eliminated from adjacent carbon atoms of C with OH group.
✓ Dehydration of an alcohol produces a mixture of alkene, the major product
obtained can be predicted by the Saytzeff’s rule.
✓ Saytzeff’s rule states that the major product in elimination reaction is the
most stable alkene which has the most highly substituted double bond.
(greater number of alkyl groups attached to the C=C)
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EXAMPLE 3
Draw the product formed for the following reaction;
a. CH3CH2CH2OH H2SO4 (conc) A
∆
H2SO4 (conc) B (major) + C (minor)
b. CH3CH(OH)CH2CH3
∆
Hc3P. O4 (conc) D
∆
Answer:
a. A : CH3CH=CH2
b. B : CH3CH=CHCH3 , C : CH2=CHCH2CH3
c. D :
EXERCISE 4 E (major) + F (minor)
Draw and give name for structure E to I
a.
H2SO4 (conc)
∆
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b.
H3PO4 (conc)
G (major) + H (minor)
∆
c. I H2SO4 (conc) CH3CH=CH2
∆
3.4 REACTION
✓ Alkene contain π (pi) bonds with delocalised π electrons.
✓ The double bond is a site of high electron density that act as nucleophilic site.
✓ Reactions of alkenes are mainly addition reactions to the double bond.
i) Hydrogenation Reaction
✓ Also known as catalytic reduction reaction
Reagent H2 (g)
Catalyst : Pd/Pt/Ni
Condition Room temperature
Product Alkane
Type of addition
reaction
Example
Pt
EXERCISE 6
Draw the product formed for the following reaction
Pd
a. (CH3)2C=CH2 + H2
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b.
+ H2 Ni
ii) Halogenation in inert solvent
Reagent Cl2 or Br2
Inert solvent such as CH2Cl2 or etc
Condition Room temperature
Product Vicinal dihalide
Type of addition
reaction
Example
CH2Cl2
iii) Halogenation in water
Reagent Cl2 or Br2
H2O
Condition Room temperature
Product Halohydrin
Type of addition
reaction
Example CH2=CH2 + X2 H2O
CH2CH2OH
X
X = Cl2 or Br2
Note:
-Addition of X and OH to the double bond must follow
Markovnikov’s Rule
-In this case, the positive ion refer to X+
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MARKOVNIKOV’S RULE
In addition of HX to an unsymmetrical alkene, H atom adds to the carbon atom of the
double bond that already has the greater number of Hydrogen atoms
HX
EXERCISE 7
Draw the product formed for the following reaction
CH2Cl2
a. CH3CH2CH=CH2 + Br2
b. H2O
+ Cl2
iv) Acid catalyst hydration
Reagent H3O+ or
H2O, H+
Condition Room temperature
Product alcohol
Type of addition
reaction
Example
✓ The addition of H and OH follow Markovnikov’s Rule
✓ Hydration of alkene is the reverse of dehydration of alcohols (subtopic
3.3)
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EXERCISE 8 CHAPTER 3: ALKENES | CHEMISTRY UNIT KMKt 2021/2022
Draw structure for J and K J
a.
H3O+
b. K H2O
H+
v) Hydrohalogenation
Reagent HBr or HCl
Condition Room temperature
Product haloalkane
Type of addition
reaction
Example
✓ The addition of H and X are follow Markovnikov’s Rule
✓ Mechanism for the reaction as follows;
✓ [Step 1]: formation of carbocation and halide ion
✓ [Step 2]: Halide ion donate electron pair to carbocation
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vi) Addition of hydrogen bromide, HBr in the presence of peroxide
Reagent HBr
peroxide (ROOR, example; H2O2)
Condition Room temperature
Product haloalkane
Type of addition
reaction
Example
✓ The addition of H and X are follow anti-Markovnikov’s
Rule
EXERCISE 9
Draw the major product formed and write the mechanism involved in reaction a)
H2O2
3.5 UNSATURATION TEST
✓ There are two chemical test used to detect the presence of the C=C bond
in a molecule.
i) Baeyer’s Test
Reagent Dilute, alkaline KMnO4
Condition cold
Product diol
Type of addition
reaction
Example
H +H KMnO4 OH-,cold HH
C
C +H3C C C CH3 MnO2
H3C
CH3 (purple) OH OH (brown precipitate)
Observation Purple colour of KMnO4 decolourised and brown
precipitate formed.
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ii) Reaction with bromine in CH2Cl2
Reagent Br2
Inert solvent (CH2Cl2)
Condition Room temperature or in the dark
Product Vicinal dihalide
Type of addition
reaction
Example CH2Cl2
dark
Observation The reddish brown color of bromine decolourised
EXERCISE 10
Write the structural formula for the products form when 1–butene reacts with each of the
following reagents:
(a) HBr
(b) H2, Pt
(c) Br2 in CH2Cl2
(d) cold dilute alkaline solution of KMnO4
Prepared by: Revised by:
SHARIFAH FADTHYAH BT SYED BAHARUDDIN AHMAD AFFENDY BIN ABDULLAH
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TUTORIAL
SECTION A
1. The IUPAC name for the following compound is
CH3 CH3
C= C CH2CH(CH3)CH3
C2H5
A cis-3, 4, 6-trimethylhept-3-ene
B trans-3, 4, 6-trimethylhept-3-ene
C cis-2-ethyl-3, 5-dimethylhex-2-ene
D trans-2-ethyl-3, 5-dimethylhex-2-ene
2. 4-chlorobut-1-ene is the name of which among the following alkenes?
A CH2Cl-CH2=CH-CH2
B CH2Cl-CH2-CH-CH2
C CH2Cl=CH2-CH=CH2
D CH2Cl-CH2-CH=CH2
3. Which among these is not a structural isomer of the compound C4H8?
A But-1-ene
B But-2-ene
C But-3-ene
D 2-methylpropene
4. Select the incorrect statement regarding alkenes.
A In alkenes, the carbons are connected by pi bonds
B Alkenes have almost same physical properties as that of the alkanes
C Alkenes are less reactive than alkanes
D Alkenes undergo polymerization reaction
5. Which of the following reactions is common in alkenes?
A Addition
B Rearrangement
C elimination
D substitution
6. Cis-trans isomerism in alkenes is due to
A chiral carbon
B free rotation about single bond
C free rotation about the double bond
D restricted rotation about the double bond
7. By using Saytzeff’s rule, the most stable alkene is
A (CH3 CH2)2C=CH2
B CH2=CHCH2 CH2 CH2 CH3
C (CH3)2C=C (CH3)2
D CH3 CH2CH=CH CH3 CH2
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8. When propene is oxidised by cold, dilute KMnO4 in NaOH solution, the product
formed is
A CH3 CH CH3
OH
B CH3CH CH2
O
C CH3CH2CH2OH
D CH3CH(OH)CH2OH
9. Cyclohexane and cyclohexene can be differentiated by using
A NaOH(aq)
B NaOH (aq) and Br2/CH2Cl2
C Br2/CH2Cl2
D Br2/CH2Cl2 and Cold KMnO4/OH−
10. Which compounds shows cis- trans isomerism?
I. CH3CH2CH = CH2
II. ClCH2CH = CHCH2Cl
III. CH3CH2 C(CH3) = CHCH3
A I & II
B II & III
C I, II & III
D I & III
SECTION B
1. Give the IUPAC names for the following alkenes:
(a) CH3CH2CH2CH=CHCH3 (b) CH3CH(CH3)CH=C(CH3)2
CH3 CH3 CH2 CH2 CH2 CH3
(c) CH3 C CH2 CC
(d) H H
H3C CH CH3 (f)
CH3CH2 C CH CH CH2CH3
(e) CH2 CH3
Cl
(g) (h)
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2. Draw the structural formula for each of the following alkenes:
(a) 2,3-dimethyl-2-pentene
(b) 4,5-dibromo-1-hexene
(c) trans-2-butene
(d) cis-2-butene
(e) 1,2-dichlorocyclobutene
(f) trans-1-chloro-2-butene
(g) isopropylcyclopentene
3. (a) Define Saytzeff’s rule.
(b) Draw the structure of compound A to E in the following reaction:
(i)
OH conc. H2SO4 A
H3C CH CH3
(ii)
OH
CH3CH2 C CH3 conc. H3PO4 B+ C
CH3 Major Minor
(iii)
conc. H2SO4
D H2C CH2
(iv) conc. H2SO4 CH3
E
4. Dehydration of sec-butyl alcohol with concentrated sulphuric acid yields a
mixture of two alkenes. Draw all the structures of alkenes and suggest the major
product of this reaction. State the rule used for the formation of the major
product.
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5. Complete the reaction scheme:
A
G - B
CH Br H2,Pt , OH
2 2 KMnO cold
4
C2l
H3CH2C conc. H2SO4 C
HBr CH3 HCl
H D
O 2 Cl2
CH2Cl2
F 2
E
6. Compound K is formed when 3-methyl-3-hexene reacts with hydrogen chloride.
(a) Draw the structural formulae of K.
(b) State the type of reaction.
(c) State the rule used to determine the structure of K.
(d) Give one chemical test to differentiate 3-methyl-3-hexene from
3-methylhexane. State the observation and write the equation involved.
7. Complete the mechanism of the reaction that occur when
methylcyclohexene is converted to 1-bromo-1-methylcyclohexane by the
addition of HBr. Give the structure of intermediate carbocation that is
formed.
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8. Use Markovnikov’s rule to predict the major product in the following
addition reactions.
9. For reaction in 8(b), draw the reaction mechanism for the formation of
major product
10. Draw the product (label as major or minor) of the reaction between 2-methyl-
2-butene with
(a) Acidified water
(b) Br2 in water
(c) HBr
(d) HBr, CH3OOCH3
11. Draw the cycloalkene that reacts with Cl2 to give
(a) (b)
(c)
12. What are the suitable reagents and conditions used for each of the
following reactions?
a)
b)
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c)
13. Outline synthesis for the following reaction
a) chlorocyclohexane from cyclohexene
b) butane from 1-butanol
c) 1-bromo-2-methylpropane from 2-methyl-1-propanol
14. Draw and name three alkenes that can be used to prepare 3-chloro-2-
methylhexane by addition of HCl?
15. Write the chemical equation and observation when cyclopentene and
cyclopentane undergoes the following treatment;
a) Addition Br2 (in CH2Cl2) in the presence of light
b) Addition Br2 (in CH2Cl2) in the absence of light
c) Addition of dilute alkaline KMnO4
Revised by:
Ahmad Affendy bin Abdullah
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CHAPTER 4: AROMATIC COMPOUNDS | CHEMISTRY UNIT KMKt 2021/2022
CHAPTER 4: AROMATIC COMPOUNDS
GENERAL OVERVIEW
a) Describe i. cyclic
aromaticity ii. Planar
iii. completely conjugated
4.1 Introduction iv. Obey HÜckel’s Rule
b) Identify the
aromatic compound
4.0 AROMATIC 4.2 Benzene a) Draw the i. monosubstituted
COMPOUND derivatives structure and name benzene
according to IUPAC
nomenclature. ii. disubstituted benzene.
b) Draw and give example of benzene as
substituent: Phenyl (C6H5)
4.3 Chemical a) write chemical i. halogenation
properties equation for ii. alkylation
iii. acylation
iv. nitration
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4.1 Introduction to Aromatic compound
• In earlier time, compounds are called aromatic because of their pleasant odours.
Such as benzaldehyde (from cherries, peaches and almond) , toluene (from Tolu
balsam), and benzene (from coal distilled).
• Today, we use the word aromatic to refer to benzene and its structural relatives.
• Arenes are aromatic hydrocarbons that contain a benzene ring as a structural
unit.
• Benzene is the simplest aromatic hydrocarbon.
• Example:
CH3
Benzene Toluene Naphthalane
Aromaticity
4 structural criteria must be satisfied for a compound to be aromatic:
1. Cyclic
➢ all p orbitals overlap each other
2. Planar
➢ All adjacent p orbitals must be aligned so that the electrons can be
delocalized
3. Completely conjugated
➢ all p orbitals overlap each other
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4. Obeys HÜckel’s Rule
➢ The number of electrons must be 4n+2, where n = 0,1,2,3,4…
• Aromatic compound is a cyclic conjugated unsaturated molecule or ion that is
stabilised by electrons delocalization.
• Benzene are aromatic compound because it contains 6 electrons (obeys HÜckel’s
Rule), cyclic, planar and have double bond in the ring.
• Identify aromatic compound,
Aromatic compound Aromatic compound
with a single ring with a multiple rings
Structure
Cyclic 4n + 2 = 6 4n + 2 = 10
Planar n=1 n=2
Completely conjugated
Obeys HÜckel’s Rule
EXAMPLE 1
Identify the aromaticity of the compounds below
Kekulé Structure of Benzene
• The molecular formula of benzene is C6H6
• August Kekulé (1872) proposed a cyclic structure for benzene.
• The Kekulé structure of benzene can be written as a six-membered ring of carbon
atoms with alternating single and double bonds.
• One hydrogen atom is attached to each carbon atom.
• The benzene ring is planar and all the carbon-carbon bonds are the same length.
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H
HH
or
HH
H
Resonance structure
• Each carbon atom is sp2 hybridized, thus has pure 2p orbital with single electron in
it.
• The six 2p orbitals overlap to form three delocalised bonds.
• As a result, the resonance structure of benzene is a hybrid resonance from two
Kekulé structure as shown below:
4.2 Benzene derivatives
Nomenclature Of Benzene Derivatives
i. MONOSUBSTITUTED BENZENE.
• To name a benzene ring with one substituent, name the substituent and add
the word benzene
• Carbon substituents are named as alkyl groups
• Benzene is the parent name and the substituent is indicated by a prefix.
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Structural formula Common name IUPAC NAME
Toluene Methylbenzene
CH3
Phenol Hydroxybenzene
OH
Benzoic Acid Phenylmethanoic Acid
COOH
Aniline Aminobenzene
NH2
O
CH
Benzaldehyde Phenylmethanal
O
C CH3
Acetophenone 1-Phenylethanone
Table 4.1 : Common Names Of Some Aromatic Compound
ii. DISUBSTITUTED BENZENE
▪ Disubstituted benzenes are named using one of the prefixes orto- (o), meta-(m) or
para-(p)
▪ Substituents are numbered so as to give the lowest set of locant.
i. ortho (o) – 1,2 ( next to each other in a benzene ring)
ii. meta (m) – 1,3 ( separated by one carbon in a benzene ring)
iii. para (p) – 1,4 ( across of each other in a benzene ring)
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• C atom bearing the substituent that defines the new parent name is numbered as
C1.
• Select one of the substituent that give new parent name and numbered as C1.
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BENZENE AS SUBSTITUENTS ~ PHENYL
• If alkyl substituent is larger than the ring (more than 6 C), the compound is named
as phenyl-substituted alkane.
• Phenyl group ( C6H5-R) can be formed by removing a hydrogen from benzene and
attaching a substituent to where the hydrogen was removed.
• To this phenomenon, we can name compounds formed this way by applying this
rule: (phenyl + substituent).
• For example, a chlorine attached in this manner would be named phenyl chloride,
and a bromine attached in this manner would be named phenyl bromide.
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• If alkyl substituent is larger than the ring, the compound is named as phenyl-
substituted alkane
• If the chain is have C═C @ C≡C @ important functional group, the benzene
ring is considered as phenyl substituent
•
EXERCISE 1:
Write the structural formulae of
a. 2-chloromethylbenzne
b. 2-phenylpropane
c. 2-ethylphenol
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4.3 CHEMICAL PROPERTIES
Electrophilic Aromatic Substitution
• Unlinke alkene, benzene do not reacts with all the following reactions
• The stability of π electron system will be lost if benzene undergo addition reactions.
• The most common reaction of aromatic compounds is electrophilic aromatic
substitution.
• Electrophilic aromatic substitution is the characteristic reaction of benzene.
• That is, an electrophile reacts with an aromatic ring and substitutes for one of the
hydrogen.
Chemical Reactions of Benzene
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Nitration of Benzene
• Benzene reacts rapidly with a mixture of concentrated nitric acid and concentrated
sulphuric acid to give nitrobenzene.
Halogenation
• Benzene reacts with bromine or chlorine in the presence of a Lewis acid.
• The Lewis acids commonly used are FeCl3 @ AlCl3 for chlorination and FeBr3 for
bromination.
• Why the bromination reaction needs Lewis acid?
• Bromine itself is not sufficiently electrophile to react with benzene, and the
formation of Br+ is difficult.
• A strong Lewis acid such as FeBr3 catalyzes the reaction, by forming a complex
with Br2 that react likes Br+
• Bromine donates a pair of electrons to FeBr3, forming a stronger electrophile with a
weak end Br – Br bond and a partial positive charge on the one of bromine atom.
Friedel-Crafts Alkylation
• Benzene reacts with haloalkane in the presence of Lewis acid catalyst such as
AlCl3, FeCl3 or FeBr3 to form alkylbenzene.
• General equation :
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• Benzene reacts with haloalkane in the presence of Lewis acid catalyst such as
AlCl3 or FeCl3 to form alkylbenzene.
• Rearrangement may occur, especially when 1o haloalkanes are used.
• Example
Friedel- Crafts Acylation
O
• The group R C is called an acyl group
• The reaction whereby the acyl group is introduced into a compound is called an
acylation reaction.
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EXAMPLE
EXERCISE 2
Suggest the reagents and products formed for the following reaction:
Prepared by: Revised by:
Wan Rosilah Binti Wan Llah Noor Azida binti Mohd Yusoff
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TUTORIAL
SECTION A
1. What is an aromatic compound?
2. State 4 criteria must be satisfied for compound to be aromatic
3. By using Huckel’s rule, determine which of the following compounds is/are aromatic?
+
A BC
4. Write the IUPAC names for the following compounds.
a) CH3
b) I
Br
c) COOH
Cl
d) CH3 CH2 CHCOOH
e) OH
f) I Br
CH3
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5. Draw the structural formula for each of the following compounds.
a) m-iodophenol
b) Isopropylbenzene.
c) 2-nitrotoluene
d) 2-phenyloctane
6. Draw the structural formula for each of the following compounds.
a) Toluene
b) Phenol
c) Aniline
d) Benzaldehyde
e) Benzoic acid
f) Acetophenone
7. Draw and name all possible aromatic compounds with the formula C7H7Cl
8. State either the following is para, meta, or ortho substituted.
NH2 CH3 HOOC
CH CH3
CH3
Cl W
UV
9. Starting from benzene, outline a synthesis of
a) ethylbenzene
b) chlorobenzene
10. Draw the structural formulae of compounds A to E and give reagent F in the following
reactions
+ Cl2 AlCl3 A
a)
b)
+ conc. HNO3 conc. H2SO4 B
50 °C - 55 °C
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c)
+C D O
CH3
d)
CH3
F
+E
11 Identify the haloalkane that might be used in a Friedel-Crafts Alkylation reaction to
prepare each of the following compounds.
a)
CH3
CH CH2 CH3
b)
12. Identify the acyl chloride that might be used in a Friedel-Crafts Acylation reaction to
prepare each of the following acylbenzenes.
O
a)
O
b)
13 Q , C7H8, is a derivative of benzene that is less toxic. Draw the structure of Q, give
the IUPAC and common name of Q. With the aid of an equation, describe briefly how
Q can be synthesised from benzene. Give the name and type of reaction.
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14 Draw the structural formulae of compounds G to J in the following reaction scheme.
a)
H
Br2
FeBr3
CH3Cl conc HNO3 I
G
conc H2SO4
AlCl3 50-55 °C
CH3COCl
AlCl3
J
b) State the name of reaction for the formation of G
c) What is the function of H2SO4 in the formation of I
SECTION B
1. Choose the CORRECT statement for the reaction below.
conc HNO3 NO2
conc H2SO4
50 - 55 °C
A. It is an addition reaction.
B. The electrophile is H2SO4.
C. It is an electrophilic aromatic substitution.
D. HNO3 donates a pair of electrons.
2. What is the function of Lewis acid in halogenation of benzene?
A. It produces a nucleophile.
B. It produces an electrophile.
C. It initiates the formation of halogen radical.
D. It decreases the polarity of halogen molecule.
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3. Which of the following compounds is aromatic?
A. C.
B. D.
4. Identify the CORRECT statement which is related to aromatic hydrocarbon
A. It has only sigma bonds
B. It has only pi bonds
C. It has a sigma and two pi bonds
D. It has a sigma and delocalized pi bond
5. Arenes are:
A. volatile
B. Water soluble
C. Non-carcinogenic
D. Mostly gases
6. How many dibromobenzenes are possible?
A. 1
B. 2
C. 3
D. 4
7. Which of the following statements is INCORRECT for an aromatic compounds
A. Are planar
B. Have 4n π-electrons
C. Are cyclic
D. Are generally less reactive than similarly substituted alkenes
8. What is the molecular formula of Benzene
A. C6H12
B. C6H6
C. C6H10
D. C8H8
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