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1
DR. JOAZAIZULFAZLI JAMALIS
Department of ChemistryFaculty of Science
Universiti Teknologi [email protected]
2
Hydrocarbons
Aliphatic Aromatic (Arenes)
• Alkane • Alkene • Alkyne
Benzene&
derivatives
3
Alkanes all bonds are single bonds (C-C and C-H, bonds) Known as saturated
hydrocarbons Categorized as acyclic or cyclic General formula for acyclic
alkanes: CnH2n+2
General formula for cyclic alkanes:
CnH2n
4
Acyclic alkanes contain only linear and branched chains of carbons atoms.
5
Cyclic alkanes are also known as cycloalkanes.
6
Alkanes Homolog Number of Carbon Atoms Methane 1Ethane 2Propane 3Butane 4Pentane 5Hexane 6 Heptane 7Octane 8Nonane 9Decane 10
7
Cycloalkanes Homolog
Number of Carbon Atoms Cyclopropane 3Cyclobutane 4Cyclopentane 5Cyclohexane 6Cycloheptane 7
8
Types of Carbons and HydrogensC - primary (1), secondary (2), tertiary (3) & quaternary (4)
H - primary (1), secondary (2) & tertiary (3)
CH
HHCHCH
HCH
HH
C HH
H
3o
3o 2o
2o
2o
1o
1o
1o1o1o
1o
1o
1o
1o
1o
TRY THIS !!!
9
C
C
C
CC C
HH
HH
HH
H
H
H
HH
HH
H
10
Alkyl Groups- removing one hydrogen atom from the alkane
- substituent groups
- The symbol is R.Alkane Alkyl group AbbreviationCH3-H
methaneCH3-
methylMe-
CH3CH2-Hethane
CH3CH2-ethyl
Et-
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Propyl (remove 1 H from propane)
CH3CHCH3
Isopropyl (remove 2 H from propane)
CH3CH2CH2
CH3CH2CH3propane
12
n- Butyl (remove 1 H from butane) CH3CH2CH2CH2
sec-Butyl (remove 2 H from butane) CH3CH2CHCH3
CH3CH2CH2CH3n-butane
13
isobutyl (remove 1 H from isobutane) C
CH3H3C
HCH2
tert-butyl or t-butyl (remove 3 H from isobutane) C
CH3H3C CH3
CH3CHCH3CH3
isobutane
14
IUPAC NAMESInternational Union of Pure and Applied
Chemistry
Rule 1: Determine the main chain1. Find the longest continuous chain of carbon atoms, and name it.2. Use the chain with greater number of substituents as the main chain.3. Substituents can be an alkyl groups, hydroxyl groups (-OH), halogen (-Cl,-Br,-I,-F), phenyl groups etc.
CH3CH2CH2CH2CHCH2CH2CH3CH3
12345678
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CH3CHCH2
CH- CHCH2CH3
CH3
CH3CH- CH3CH3
4. Determine the chain with the greater number of substituents
CH3CH2CH2CH2CHCH2CH3CH2CH2CH3
123
45678
16
17
Rule 2 & 3: Numbering the Main Chain and naming the
alkyl groups
1. Number the longest chain, start with the end of the
chain nearest to a substituent2. Substituted carbons always get the lowest
possible number
CH3CHCH2CH2CH3CH3
1 2 3 4 5
2-methylpentane (IUPAC)isohexane (common name)
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CH3CH2CHCHCHCH2CH3
CH3
CH3
CHCH3
CH31
2
34567
3-ethyl-2,4,5-trimethylheptane
19
when two or more substituents are present, list them in alphabetical order. when two or more of the same alkyl groups (or other substituent) are present, use the prefixes di-, tri-, tetra-, hexa- etc. follow the alphabet of the alkyl groups, NOT the prefixes di-, tri-, tetra- (IGNORE alphabet of the prefixes)
Rule 4: Organizing multiple groups
CH3CHCHCH2CHCH2CH3
CH2CH31 2 3
4 5 6 7
CH3
CH3
5-ethyl-2,3-dimethylheptane
20
CH3CH2CCH2CH2CHCHCH2CH2CH3
CH2CH31 2 4 5 6 7
CH2CH3 CH2CH3
CH33
8
9 10
3,3,6-triethyl-7-methyldecane
CH3CH2CHCH2CHCH2CH2CH3CH3 CH2CH3
1 2 3 4 5 6 7 8
5-ethyl-3-methyloctane
21
When both directions lead to the same lowest number for one of the substituents, choose the direction that gives the lowest possible number to the remaining substituents.
CH3CCH2CHCH3CH3
CH3
CH3
2 4
2,2,4-trimethylpentaneNOT
2,4,4-trimethylpentane
22
CH3CH2CHCHCH2CHCH2CH3CH3
CH3 CH2CH31 3 4 6
6-ethyl-3,4-dimethyloctane [6,3,4] NOT3-ethyl-5,6-dimethyloctane [3,5,6]
23
If the same number is obtained in both directions, follow the alphabet of the substituent.
CH3CH2CHCHCHCH2CH3
CH3 CH2CH3
CH3134
5
3-ethyl-4,5-dimethylheptane
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CH3CHCHCH3
Cl
Br
2-bromo-3-chlorobutaneNOT
3-bromo-2-chlorobutane
CH3CH2CHCH2CHCH2CH3
CH2CH3
CH3
3-ethyl-5-methylheptaneNOT
5-ethyl-3-methylheptane
25
Certain common names are still used in the IUPAC system Eg.
CH3CHCH2
CH3CH3CH
CH3
Isopropyl Isobutyl
CH3CH2CH2CH2CHCH2CH2CH3CHCH3CH3
4
1 2
4-isopropyloctane or 4-(1-methylethyl)octane
26
CH3CH2CH2CH2CHCH2CH2CH2CH2CH3CH2CHCH3
CH3
5
1 2 3
5-isobutyldecaneor
5-(2-methylpropyl)decane
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Cycloalkanes Rings of carbon atoms (CH2 groups) Formula: CnH2n
Nonpolar, insoluble in water Compact shape Melting and boiling points similar to branched alkanes with same number of carbons
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Nomenclature of Cycloalkane
H3C Cl
methylcycloheptane chlorocyclohexane
no number is needed for a single substituent on a ring
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CH3
CH2CH2CH2CH2CH3
methylcyclopentane
1-cyclobutylpentane
May be cycloalkyl attachment to chain.
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if more than one substituent, arrange in alphabetical order
give number to the carbon of the ring choose the “best” combination of numbers
CH2CH3H3C
CH3CH2CH2 1
23
12
3
4
4
4-ethyl-2-methyl-1-propylcyclohexaneNOT
1-ethyl-3-methyl-4-propylcyclohexaneNOT
5-ethyl-1-methyl-2-propylcyclohexane[4,2,1]=7[1,3,4]=8[5,1,2]=8
31
H3C CH3CH3
1,1,3-trimethylcyclopentaneNOT
1,3,3-trimethylcyclopentaneNOT
1,1,4-trimethylcyclopentane
32
Complex Substituents If the branch has a branch, number the
carbons from the point of attachment. Name the branch off the branch using a
locator number. Parentheses are used around the complex
branch name.
1 23
1-methyl-3-(1,2-dimethylpropyl)cyclohexane
33
Isomerism
Molecules which have the same molecular formula, but differ in the arrangement of their atoms, are called isomers.
Constitutional (or structural) isomers differ in their bonding sequence.
Stereoisomers differ only in the arrangement of the atoms in space (in alkene).
34
Structural Isomers
CH3CH2OHO CH3H3C and
C4H1
0
CH3CH2CH2CH3 and CH3CHCH3
CH3
C2H6O
35
Geometric Isomerism in CycloalkanesThe lack of free rotation of single-bonded
carbons in a ring produces a kind of isomerism called geometric isomerism.
CH3CH3
HH
cis 1,2-dimethylcyclopropane
HCH3
CH3H
trans 1,2-dimethylcyclopropane
36
1. Natural gas methane (60%-80%) ethane, propane and butane
2. Petroleum gasoline C5H12-C12H26 kerosene C12H26-C16H34 diesel fuel C15H32-C18H38
Source of alkanes
37
Physical Properties of Alkanes1. Alkanes from C1 to C4 are gasses
C5 to C17 are liquids >C18 are wax-like solids
2. Alkanes are nonpolar compounds. Their characteristic known as “like
dissolves like” rule. Nonpolar compounds are soluble in
other nonpolar solvents. Alkanes are soluble in organic
solvents.
38
3. Boiling Points (bp)a. Alkanes have low bp’s compared to
more polar compounds of comparable size
CH3CH2CH3 CH3CH2OHCH3CHO
MW= 44BP= -42oC
Van der Wall forces (weak)
MW =44BP=21oC
dipole-dipoleattraction
MW = 46BP=79oC
hydrogen bonding (strong)
39
b. Boiling points(b.p) increases as the numbers of carbons increases because of increased surface area
CH3CH2CH2CH3 b.p = 0oC
CH3CH2CH2CH2CH3 b.p = 36oC
CH3CH2CH2CH2CH2CH3 b.p = 69oC
40
c. The b.p of isomers decrease with branching
because of decreased surface areabranched alkanes are more compact, less surface contact between molecules, less van der Waals attractions.
CH3CH2CH2CH2CH3CH3CH2CHCH3
CH3b.p = 36C b.p = 28C
CH3CCH3CH3
CH3
b.p =10C
41
Synthesis of Alkanes1. Hydrogenation of Alkenes
Alkene + H2 Alkane Catalyst required, usually Pt, Pd,
or Ni.
42
2. Reduction of alkyl halide Sources of H: Zn / CH3COOH, LiAlH4,
NaBH4
CH3CH2CH2CH2Br CH3CH2CH2CH3LiAlH4
HCl Zn
CH3COOH
HH
ZnCH3COOHR X R H
orLiAlH4
43
3. Reduction of alkyl halide via Grignard Reagent add an organometallic reagent to water this will reduce an alkyl halide to an alkane
R + HMgX O H R H Mg(OH)X+
Grignard Reagent react with water molecule:
44
Reactions of Alkanes1. Combustion
2. Cracking and hydrocracking (industrial)
3. Halogenation
2 CH3CH2CH2CH3 + 13 O2heat
8 CO2 + 10 H2O
CH4 + Cl2heat or
light CH3Cl + CH2Cl2 + CHCl3 +CCl4
long chain alkane shorter chain alkanecatalyst
45 45
Mechanism of HalogenationStep 1 (Initial Step)Homolytic cleavage of the chlorine molecule
Cl Cl hvor heat
2 Cl
Step 2 (Propagation Step)i) Chlorin radical attack alkane molecule to form alkyl radical
ii) Alkyl radical will attack chlorine molecule to produce chlorine radical
R + + ClCl Cl R Cl
ClR H + HCl + R
46
Step 3 (Termination Step)Free radicals will combine or transfer its electrons to form a molecule
R + R R R
Cl + Cl Cl Cl
R + Cl R Cl
Halogenation will give mixtures of products because
there are more than one atom of hydrogen that will be substituted.
47
Try This !!!
Propose the mechanism for the following reaction. Which compound is the major product. Explain your answer.
CH3CH2CH3 + Cl2heat oruv light
?