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Dr Nik Ahmad Nizam Bin Nik Malek, BSc (Ind. Chem.)(UTM), MSc (Chem)(UTM), PhD (Chem)(UTM), A.M.I.C
Senior Lecturer,
Department of Biotechnology and Medical Engineering
Faculty of Biosciences and Medical Engineering
Alkenes, Alkynes and Aromatic
BIO-ORGANIC CHEMISTRY (Organic Chemistry for Biology Students)
(SQBS 1603)
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Functional groups
What is functional group? The chemical components that are added to the simple skeleton of an organic
compound.
To generate chemical diversity and functionality.
Molecules possessing the same functional group
belong to the same family of organic compounds.
Groups containing halogens
Hydrocarbon
Groups containing oxygen
Groups containing nitrogen
Groups containing phosphorus and sulfur
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Chemical class Group Formula Structural Formula
Prefix Suffix
Alkane Alkyl RH alkyl- -ane
Alkene Alkenyl R2C=CR2 alkenyl- -ene
Alkyne Alkynyl RC≡CR' alkynyl- -yne
Benzene derivative
Phenyl RC6H5 RPh
phenyl- -benzene
Toluene derivative
Benzyl RCH2C6H5 RBn
benzyl- 1-(substituent)toluene
Functional groups
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Alkenes and alkynes • Alkenes
– Organic compounds that contain a carbon-
carbon double bond
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CH3CH2CH2CH=CHCH2CH2CH3
C
H
H
H C
H
H
C
H
H
C
H
H
C
H
H
HC
H
C
H
Hept-3-ene
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Alkenes and alkynes
• Alkynes
– Organic compounds that contain a carbon-
carbon triple bond
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CH3CH2CH2C=CCH2CH2CH3
C
H
H
H C
H
H
C
H
H
C
H
H
C
H
H
HC C
Hept-3-yne
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Nomenclature (Alkenes)
6
Find the base structure The longest chain that contains the largest possible number of double bonds.
Naming suffix = –ene (2 No. C=C:-diene, 3 No. C=C: -triene, 4 No. C=C: -tetraene and so on.
C: 7 heptene
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Numbering start from the end closest to C=C.
7
1
2
3
4
5
6
7
1-heptene
Nomenclature (Alkenes)
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Nomenclature (Alkenes)
8
1
2
3
4
5
6
7
3-propyl-1-heptene
propyl
Position 3
If there is substituent insert number before its name.
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Nomenclature (Alkenes)
1
2
3
4
5
6
7
Hept-2,4-diene
propyl
Position 3
3-propyl-hept-2,4-diene
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Nomenclature (Alkynes)
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IUPAC or Systematic name
Similar to the naming of alkenes
But-2-yne
But-1-yne
3-Methyl-hept-1-yne
5-Methyl-hept-3-yne
6-Methyl-octa-2,4-diyne
6-Methyl-oct-4-en-2-yne
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Cycloalkenes
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Cyclopropene Cyclobutene Cyclopentene Cyclopenta-1,3-diene
Cyclohexene Cyclohexa-1,3-diene Cycloheptene Cyclohepta-1,2,4-triene
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Stereoisomers • Stereoisomers posses the same atoms, which exhibits the same
connectivity but the composite atoms are oriented differently in space.
• Different configuration.
• Differ only in the 3-dimensional arrangement of atoms.
• Two classes
1. Geometric (cis-trans) isomers.
2. Enantiomers.
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But-2-ene
C C
H3C
H
CH3
H
But-2-ene
C C
H3C
H
H
CH3
But-2-ene
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But-2-ene
C C
H3C
H
CH3
H
But-2-ene
C C
H3C
H
H
CH3
But-2-ene
Geometric (cis-trans) isomers
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Geometric (cis-trans) isomers
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C C
A
B
C
D
These two groups must be different from each
other….
And these two groups must
also be different from each other….
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Geometric (cis-trans) isomers
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C C
H3C
H
CH3
H
But-2-ene
C C
H3C
H
H
CH3
But-2-ene
Cis isomers Trans isomers
Methyl groups on the same
side
Methyl groups on the
opposite side
Cis-2-butene Trans-2-butene
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Reactions of Alkenes
• Addition reaction
– Reaction in which elements are added to a
compound
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C C X Y C
X
C
Y
One bond is broken
2 single bonds are formed
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Reactions of Alkenes • Four addition
reactions of alkenes
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H
H
H
H
H
H
H
H
X
X
H
H
H
X
H
H
H
OH
H2
X2
HX
H2O
Metal catalyst
X = Cl or Br
H2SO4
Hydrogenation
Halogenation
Hydrohalogenation
Hydration
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Hydrogenation
• Addition of hydrogen
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C C H H C
H
C
H
catalyst by metal
Alkane
Alkene E.g. Pd
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Halogenation
• The addition of halogen (X2) to an alkene
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C C X X C
X
C
XX = Cl or Br
Alkene Alkyl dihalide
C C
H
H H
H
Cl2 C
Cl
H
CH H
Cl
H
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Hydrohalogenation • The addition of HX (X = Cl or Br) to
an alkene
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C C H-X C
H
C
XX=Cl or Br
C C
H
H H
H
HCl C
H
H
CH H
Cl
H
Alkene Alkyl
halide
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Hydrohalogenation
• Markovnikov’s rule
– In the addition of HX to an unsymmetrical
alkene, the H atom bonds to the less
substituted carbon atom
The carbon that has more H’s to begin
with.
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Hydrohalogenation
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C C
H
H3C H
H
HCl C
H
H
CH3C H
Cl
H
C
Cl
H
CH3C H
H
H
or
1-Chloro-propanePropene
2-Chloro-propane
C C
H
H3C H
H
According to Markovnikov’s rule
the H atom bonds to the less substituted carbon atom (has more H’s )
Only product
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Hydration
• The addition of water (H2O) to an alkene
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C C H-OH C
H
C
OHH2SO4
Alkene Alcohol
C C
H
H H
H
H-OH C
H
H
CH H
OH
H
H2SO4
EthanolEthene
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Hydration
• The hydration of unsymmetrical
alkene follows markovnikov’s rule
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H2SO4
C C
H
H3C H
H
H-OH C
H
H
CH3C H
OH
H
C
OH
H
CH3C H
H
H
or
PropenePropan-2-olPropan-1-ol
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Benzene and aromatic compounds
• Unsaturated hydrocarbons
• Benzene
– The simplest and widely known aromatic compound
– Six-membered ring and 3 double bonds.
– Molecular formula: C6H6
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C
C
C
C
C
CH
H
H
H
H
H
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Benzene
• Resonance structures
– Lewis structure with the same arrangement of
atoms but a different arrangement of electrons
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Aromatic compounds and conjugated bonds
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C
C
C
C
C
CH
H
H
H
H
H
alternating C-C and C=C
ring structure of benzene created from the joint of C atoms
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C
C
C
C
C
CH
H
H
H
H
H
Actually
• C atoms are not joined by
alternating C-C and C=C:
•But, by a network of bonds that
fall halfway between single and
double.
So what is happening here?
How can there be this ‘special’ bond
network?
Aromatic compounds and conjugated bonds
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C C
C
C C
C
H
H
H
H
H H
C
C
H
C
Each C atom contributes 3 valence electrons to 3 single covalent bonds
3 bonds containing 3 valence electrons from the central C
atom
The fourth valence electron occupies a p orbital
Aromatic compounds and conjugated bonds
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The p orbital on adjacent C atoms
overlap
The p orbitals of 6 C atoms that form a benzene ring overlap to form an unusual pi () orbital, which takes the form of two doughnut-shaped rings.
Two doughnut-shaped rings form a unique -bond above and
below the benzene ring
Aromatic compounds and conjugated bonds
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The valence electrons occupying the overlapping orbitals are not restricted to being associated with one or two specific C atoms
free to move anywhere within the doughnut-shaped bond
Aromatic compounds and conjugated bonds
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Conjugated system Overlap of p-orbitals
Conjugation of bonds (to form a network of delocalized electrons)
can occur wherever 2 double bonds are separated by one
single bond.
Aromatic compounds and conjugated bonds
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Aromatic compounds and conjugated bonds
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Resonance Hybrid
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Aromatic compounds and conjugated bonds
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• Aromatic compounds in biological systems
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Phenylalanine (amino acid) tyrosine (amino acid)
Aromatic compounds and conjugated bonds
H2N CH C
CH2
OH
O
H2N CH C
CH2
OH
O
OH
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Nomenclature • Monosubstituted benzenes
– Name of substituents + benzene.
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ethylbenzene butylbenzene
Cl
chlorobenzene
HO
phenol
IUPAC name:
hydroxybenzene
H2N
aniline
IUPAC name:
aminobenzene
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Nomenclature
Same disubstituted
Benzene
Ortho
Meta Para
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• Disubstituted benzene
X
Y
1,2- or ortho- (o)
1
2
X
Y
1,3- or meta- (m)
1
3
X
Y
1,4- or para- (p)
1
4
Nomenclature
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• Disubstituted benzene
– Example
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o-Xylene
1,2-dimethylbenzene (IUPAC)
m-Xylene
1,3-dimethylbenzene (IUPAC)
p-Xylene
1,4-dimethylbenzene (IUPAC)
Nomenclature
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• Disubstituted benzene
– Example
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CH2CH3
CH2CH3
CH2CH3
CH2CH3
CH2CH3
CH2CH3
1,2-Diethyl-benzene1,3-Diethyl-benzene
1,4-Diethyl-benzeneortho-diethyl-benzene or
o-diethyl-benzene
meta-diethyl-benzene or
m-diethyl-benzene para-diethyl-benzene or
p-diethyl-benzene
Nomenclature
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• Disubstituted benzene
– Different substituents alphabetize the
name of the substituents.
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Br
Cl
1-Bromo-2-chloro-benzene
CH3
CH2CH3
1-Ethyl-3-methyl-benzene
Nomenclature
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• Polysubstituted (Three or more
substituents) benzenes
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1
2 4
3
1. Assign the lowest set of number 2. Alphabetize the names of all the substituent
ethyl
propyl methyl
1-ethyl-4-methyl-2-propylbenzene
Nomenclature
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• Polysubstituted (Three or more
substituents) benzenes
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Cl
NH2
Cl
aniline
1. The common root = aniline 2. Alphabetize the names of all the substituent
1
2
3
4 5
2,5-dichloroaniline
Nomenclature
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• Aromatic compounds with more than one
ring
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Naphthalene1,6-Dimethyl-naphthalene
1-Ethyl-2,6-dimethyl-naphthalene
Anthracene
3-Ethyl-1,10-dimethyl-anthracene
Nomenclature
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Reaction of aromatic compounds
• Aromatic compounds undergo substitution not addition
• Substitution
– A reaction in which an atom is replaced by another atom or a group of atoms.
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C
C
C
C
C
CH
H
H
H
H
H
X-Y
C
C
C
C
C
CH
H
X
H
H
H
H-Y
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• No addition reaction for benzene
• C=C in Benzene ≠ C=C in alkene
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C
C
C
C
C
CH
H
H
H
H
H
X-Y
C
C
C
C
C
CH
H
X
Y
H
H
H
H
Reaction of aromatic compounds
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• Three specific reactions
– Chlorination -Cl
– Nitration -NO2
– Sulfonation -SO3H
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Reaction of aromatic compounds
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Cl Cl
Cl
H Cl
Benzene
Catalyze by FeCl3
Product: aryl halide
Reaction of aromatic compounds
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Nitration
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HNO3
NO2
H OH
Benzene
Catalyze by H2SO4
Product: nitrobenzene
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Sulfonation
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SO3
SO3H
Benzene
Catalyze by H2SO4
Product: benzenesulfonic acid
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REFERENCES
• Crowe, J., Bradshaw, T. and Monk, P. (2006), Chemistry for the Biosciences: The Essential Concepts, Oxford University Press, Oxford.
• Horton, H.R., Moran, L.A., Scrimgeour, K.G., Perry, M.D. and Rawn J.D. (2006). Principles of Biochemistry, 4th Edition. Pearson International Edition.
• Smith, J.G. (2010). General, Organic and Biological Chemistry. McGraw-Hill Higher Education.
• Denniston, K.J., Toping, J.J. and Caret, R.L. (2008). General, Organic and Biochemistry, 6th edition. McGraw-Hill Higher Education.
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MY PROFILE
Dr Nik Ahmad Nizam Bin Nik Malek,
BSc (Ind. Chem.)(UTM), MSc (Chem)(UTM), PhD (Chem)(UTM), A.M.I.C Senior Lecturer,
Department of Biotechnology and Medical Engineering,
Faculty of Biosciences and Medical Engineering,
Universiti Teknologi Malaysia.
Email: [email protected] , [email protected]
Website: http://www.staff.blog.utm.my/niknizam/