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Hydrocarbons
Lecture no. 29-32
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Organic Compounds
Contain carbon
Have covalent bonds
Have low melting points
Have low boiling points
Burn in air (oxygen)
Generally soluble in nonpolar solvents
Form large molecules
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24.1
Common Elements in Organic Compounds
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Classification of organic compounds:
Classes of organic compounds could be distiguished according to
the functional group that the compound contains.
A functional group is a group of atoms that is largely responsible
for the chemical behavior of the parent molecule.
Most organic compounds are derived from hydrocarbons.
On the basis of structure hydrocarbons are divided into two main
classes- aliphatic and aromatic.
Aliphatic hydrocarbons are further divided into: alkanes, alkenes,
alkynes and cycloalkanes.
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24.1
Classification of Hydrocarbons
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Alkanes
Contain C and H only
Contain single bonds C-C
Have 4 bonds to every carbon (C) atom
Are nonpolar
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Alkanes
Alkanes have the general formula CnH2n+2 where n= 1,2,3,
only single covalent bonds
saturated hydrocarbons because they contain the maximum
number of hydrogen atoms that can bond with the number of carbon
atoms in the molecule
CH4 C2H6 C3H8
methane ethane propane
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Structural isomers are molecules that have the same molecular
formula but different structures
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How many structural isomers does pentane, C5H12, have?
C C C C C
H H H H H
H
HHHHH
H
C C C C
H CH3 H H
H
HHHH
H
C C C
H CH3 H
H
HH
H
CH3
n-pentane
2-methylbutane
2,2-dimethylpropane
24.2
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Isomers could only be distinguished by their systematic names or
IUPAC nomenclature.Decan has 75 isomers.
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Alkane Nomenclature
1. The parent name of the hydrocarbon is that given to the longest
continuous chain of carbon atoms in the molecule.
CH3 CH2 CH2 CH CH2 CH2 CH3
CH3
1 2 3 4 5 6 7
4-methylheptane
2. An alkane less one hydrogen atom
is analkylgroup.
CH4
CH3
methane
methyl
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24.2
Alkane Nomenclature
3. When one or more hydrogen atoms are replaced by other groups,
the name of the compound must indicate the locations of carbonatoms where replacements are made. Number in the direction that
gives the smaller numbers for the locations of the branches.
CH3 CH CH2 CH2 CH3
CH3
1 2 3 4 5
2-methylpentane
CH3 CH2 CH2 CH CH3
CH3
1 2 3 4 5
4-methylpentane
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24.2
Alkane Nomenclature
4. Use prefixes di-, tri-, tetra-, when there is more than one alkyl
branch of the same kind.
CH3 CH CH CH2 CH2 CH3
CH3
1 2 3 4 5 6
CH3
2,3-dimethylhexane
CH3 CH C CH2 CH2 CH3
CH3
1 2 3 4 5 6
CH3
3,3-dimethylhexane
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24.2
Alkane Nomenclature
5. Use previous rules for other types of substituents.
CH3 CH CH CH3
Br
1 2 3 4
NO2
2-bromo-3-nitrobutane
CH2 CH2 CH CH3
Br
1 2 3 4
NO2
1-bromo-3-nitrobutane
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What is the IUPAC name of the following compound?
24.2
1 2 3 4 5 6 7 8
CH3 CH CH2 CH CH2 CH2 CH3
C2H5
CH2
CH3
4-ethyl-2-methyloctane
What is the structure of 2-ethyl-4-methylhexane?
1 2 3 4 5 6CH3 CH CH2 CH CH2 CH3
CH3C2H5
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As low number as
possible
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Sum of the numbers
should be minimum
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24.2
achiral chiral
Optical isomerism in alkanes
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24.2
Cycloalkanes
Alkanes whose carbon atoms are joined in rings are called
cycloalkanes. They have the general formula CnH2n where n= 3,4,
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Cycloalkanes
24.2
http://localhost/var/www/apps/conversion/tmp/scratch_3/Models%20Tutorial%20--%20Page%2014.mht7/30/2019 Alkane Onwards
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24.2
Alkenes
Alkenes have the general formula CnH2n where n= 2,3,
contain at least one carbon-carbon double bond
also calledolefins
CH2 CH CH2 CH3
1-butene
CH3 CH CH CH3
2-butene
C C
Cl Cl
H H
C C
Cl H
H Cl
cis-dichloroethylene trans-dichloroethylene
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prepared by Dr. Harpreet Kaur
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Nomenclature of alkene:
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Cis-trans isomerism
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Cis-Trans Isomerization in the Vision Process
24.2
Alk
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24.2
Alkynes
Alkynes have the general formula CnH2n-2 where n= 2,3,4,
contain at least one carbon-carbon triple bond
1-butyne 2-butyne
CH C CH2 CH3 CH3 C C CH3
Production of acetylene
CaC2(s) + 2H2O (l) C2H2(g) + Ca(OH)2(aq)
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sp
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Reactions of alkanes: glance over types of reactions
Alkanes are generally considered unreactive, but under favorable
conditions they do react
Alk R ti
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24.2
Alkane Reactions
CH4(g) + 2O2(g) CO2(g) + 2H2O (l) DH0 = -890.4 kJ
Combustion
Halogenation
CH4(g) + Cl2(g) CH3Cl (g) + HCl (g)light
Cl2 + energy Cl
+ Cl
Cl + C HH
H
H
C H
H
H
+ HCl
CH
H
H
+ Cl Cl C ClH
H
H
+ Cl
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Reactions of alkenes
Weak electrons are attracted by electrophile and than end of
reaction is carried out by nucleophile
C2H6(g) CH2 CH2(g) + H2(g)Pt
catalyst
Cracking(prepration of alkenes)
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Markovnikovs rule: the hydrogen adds to sp2 carbon that is
bonded to greater no ofhydrogens
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prepared by Dr. Harpreet Kaur
Alkene Reactions
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24.2
Alkene Reactions
Addition Reactions
CH2 CH2(g) + HBr (g) CH3 CH2Br (g)
CH2 CH2(g) + Br2(g) CH2Br CH2Br (g)
Alkyne Reactions
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24.2
Alkyne Reactions
Addition Reactions
Hydrogenation
CH CH (g) + H2(g) CH2 CH2(g)
CH CH (g) + HBr (g) CH2 CHBr (g)
CH CH (g) + Br2(g) CHBr CHBr (g)
CH CH (g) + 2Br2(g) CHBr2 CHBr2(g)
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H3C C C CH3
xs H2
Pt
CH3CH2CH2CH3
H 2/Pd/BaSO 4
Quinoline
(Lindlar's Catalys t)
H3C
C
H
C
H
CH3
Na NH 3 (liq)
H3C
C
H
C
H
CH3
Hydrogen Halide
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prepared by Dr. Harpreet Kaur
Hydrogen Halide
Addition to AlkynesHeteroatom stabilized carbocation
intermediates
H3C C C HHX
H3C C C H
H
+
X-
H3C C C H
H
X
Markovnikov
addition
a vinyl halide
H3C C C H
H
X
HXH3C C C H
H
HX
+ X-
a heteroatom
stabilized carbocation
H3C C C H
H
HX+
H3C C C H
H
X H
X
a geminal dihalide
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Halogenation of Alkynes
Formation of Vicinal tetrahalides
C C
an alkyne
X2 C C
X X
X X
a vicinal tetrahalide
carbonte trachloride
S b tit ti
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Substitution
Alkynyl Anion Synthesis of Alkynes via
Bimolecular Nucleophilic Substitution
R C CHNa
R C C Na+
R C C Na+ + R'CH2 X R C C CH2R' + NaX
+ H2
TerminalAlkyne
Methylor
Primary
Alkyl
Halide
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Diels-Alder Reaction
Six-membered Ring formation (4+2) Diene + Dienophile
CC
CC
C
C
Examples of reactions in Alkynes
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Examples of reactions in Alkynes
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prepared by Dr. Harpreet Kaur
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Chemistry In Action: Ice That Burns
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