topic 11_introduction to organic chemistry
TRANSCRIPT
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Introduction To Organic
Chemistry
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Lecture 1
12.1 IntroductionLearning Outcomes:
At the end of the lesson the students should be able to :
1. List the elements that made up organic compounds C, H,O, N, P, S and halogens.
2. State the ability of carbon to form 4 covalent bonds withother carbons or elements.
3. Differentiate between saturated and unsaturated organic
compounds.4. Give examples of organic compounds used in medicine,
engineering, biotechnology and agriculture.
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WHAT IS ORGANIC CHEMISTRY?Organic chemistry is the chemistry of carboncompounds.
Organic compounds contain H as well as C, while
other common elements are O, N, the halogens, S andP.
There are many varieties of organic compounds
( more than 10 millions!!!)
They may exist as simple or complex molecules; asgases, liquids or solid and coloured or colourless.
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Examples:-
CH4
methane (a component of natural gas)
methyl salicylic acid (aspirin-a drug)
OCOCH3
COOH
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CH2 C
O
NH
O
S
N
COOH
penicillin (an antibiotic)
Cl CH Cl
CCl3
dichlorodiphenyltrichloroetane
(DDT- a pesticide component)
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All organic compounds consist ofcarbon atom.
Properties of carbon atom:
-has 4 valence electrons.
-can form 4 covalent bonds.
C C
Single bond
C C C C
Double bond Triple bond
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Hydrocarbons
saturated unsaturated
Contains only singlebonds ( -C-C- )
Examples: alkanes,
cycloalkanes
Contains at least onecarbon-carbon double
bond (-C=C-) or triplebond (-C C-).
Examples: alkenes,alkynes.
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Uses of organic compounds
Medicine Antibiotics are used to
fight bacterial and fungal
infections
Engineering Gasoline-as a fuel forinternal combustion
engines.
Biotechnology Genetic information like
DNA
Agriculture DDT-as insectisides to kill
harmful insects.
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Lecture 2:
12.2 Molecular and Structural Formulae
Learning Outcomes:
At the end of the lesson the students should
be able to :Define structural formula.
Draw structural formula in the form of expanded,condensed and skeletal structures based on the
molecular formula.
Explain primary (1), secondary (2), tertiary (3)and quaternary (4) carbon.
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Structural formulashows how the
atoms in a molecule are bonded to
each other.
3 types of structural formula: condensed structure
expanded structure
skeletal structure
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2- Dimensional formula
Condensed StructureDoes not show single bonds between carbonand hydrogen atoms, but double and triple bondsare shown.
All atoms that are attached to a carbon arewritten immediately after that carbon.
C4H9Cl CH3CHCH2CH3
(Condensed structure)
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H2C
CH2
CH2
CH2
H2C
H2C
Examples:
ii) Cyclohexane, C6H12 iii) Aldehyde, CH3CHO
CH3CH
O
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Expanded Structure
Expanded structures indicate how atoms are
attached to each other but are not representations
of the actual shapes of the molecules.
C4H9ClMolecular
Formula
Expanded structure
C C C CH H
H H HCl
H H H H
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Examples:
i) Alcohol (C2H6O)
ii) Carboxylic acid (C3H6O2 )
C
H
H
H
C
H
H
OH
C
H
H
H
C
H
H
C
O
OH
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Skeletal Struc tu re
Shows only the carbon skeleton.Hydrogen atoms are not written.
Other atoms such as O, Cl, N etc. are shown.
i) CH3CH(Cl)CH2CH3 =
Cl
ii) =H2C CH2
H2C CH2
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3- Dimensional formula
( wedge
dashed wedge
line formula )
Describes how the atoms of a molecule
are arranged in space.
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Example : Bromoethane
or or
Indication :-
:bonds that lie in the plane
:bonds that lie behind the plane
:bonds that project out of the plane
C
Br
H
H
H
C
Br
HH
H
C
H
BrH
H
C
H
HBr
H
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A carbon atom can be classified as
primary carbon(1o)bonded to 1 C
secondary carbon(2o) bonded to 2 C
ter tiary carbon(3o) bonded to 3 C
quarternary carbon(4o) bonded to 4 C
Classification of C atoms:
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H C H
CH3
H
10 carbon10 carbon
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H C CH3
CH3
CH3
30 carbon
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11
1
11H C C C CH2 C CH3
H
H
H
H H
CH3 CH3
CH3
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2
2H C C C CH2 C CH3
H
H
H
H H
CH3 CH3
CH3
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43H C C C CH2 C CH3
H
H
H
H H
CH3 CH3
CH3
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CH3(CH2)CCl(CH3)2
Question
CondensedStructure
ExpandedStructure
SkeletalStructure
O
C
H
HH
C CH
H
H
CH3
CH3
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12.3 FUNCTIONAL GROUPS
AND HOMOLOGOUS SERIES
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Lecture 3
Functional Group and Homologous Series
Learning Outcomes:
At the end of the lesson the students should be ableto :
Define functional group.
Name functional groups and classify organiccompounds according to their functional groups.
Define homologous series and explain generalcharacteristics of its members.
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Functional group
is an atom or group of atoms in an organic
molecule which characterised the molecule
and enables it to react in specific wayswhich determines its chemical properties.
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Functional groups are important for three
reasons:
i. A basic by which organic compounds are
divided into different classes.
ii. A basic for naming organic compounds
iii. A particular functional group will always
undergo similar types of chemicalreactions.
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Homologous Series
is series of compounds where each member
differs from the next member by a constant
CH2 unitMembers of the same homologous series
are called homologs.
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Homologs Features
1. Obey a general formula:
Examples:
Alkane: CnH2n+2 Alkene: CnH2n Alcohol : CnH2n+1OH
2.
Differ from the successive homolog by a CH2unit
3. Show a gradual change in the physical properties
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4. Have same functional group
5. Have similar chemical properties
6. Can be prepared by similar general methods
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CH3C CCH3
carbon-carbontriple bond-C C-Alkyne
CH3CH=CH2
carbon-carbon
double bond-C=C-Alkene
CH3-CH3Alkane
Example
NameStructure
Class ofCompound
Functional Group
Classification of organic compound
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Aromatic Benzene ring -CH3
Haloalkane X (F, Cl, Br, I) Halogen CH3Cl
Alcohol -OH Hydroxyl CH3-OH
Phenol -OH Hydroxyl -OH
Ether -C-O-C- Alkoxide CH3-O-CH3
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Aldehyde
-C=O
H Carbonyl
CH3-C=O
H
KetoneR-C=O
R CarbonylCH3-C=O
CH3
Carboxylic
acid
-C=O
OH Carboxyl
CH3-C=O
OH
Ester
-C-O-C-
O Carboalkoxy
CH3-C=O
OCH3
Acyl chloride
-C=O
Cl
CH3-C=O
Cl
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Anhydride
O O
-C-O-C-
O O
CH3C-O-CCH3
Amide -C=O
N-
Carboxamide CH3-C=O
NH2
Amine -NH2 Amino CH3-NH2
Nitrile -C N Cyano group CH3C N
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Exercises:
1. Identify the functional group in the following
molecules
a)(CH3)3CCH
2CH=CH
2
b)(CH3)3CCH=CHCH2-OH
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CH3 C
CH3
C C CH C NH2
O
NH2 CH
CH2
CH2
CO
OH
OH
C
O
O CH3
CH2
C
O
O C
O
CH3c)
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12.4 IsomerismLearning Outcomes:
At the end of the lesson the students should beable to :
Define isomerism.
Explain constitutional isomerism.
chain isomers
positional isomersfunctional group isomer
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Isomerism
Structural/
Constitutional IsomerismStereoisomerism
ChainIsomerism PositionalIsomerism
Functional Group
Isomerism
diastreomer enantiomer
cis- trans
isomerism
other
diastereomers
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I somerism
is the existence of different compounds with
the same molecular formula but differentstructural formulae.
Different structural formula that have the samemolecular formula are called isomers.
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1) Consti tutional isomers (Structural isomers)
are isomers with the same molecular formula
but differ in the order of attachment of atoms.2) Stereoisomers
are isomers with the same molecular formula
but different arrangement of atoms in space
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Consti tutional isomerism
Isomerism resulting from different order of
attachment of atoms.
Three types
a) Chain/skeletal isomer ism
b) Positional isomerism
c) Functional group isomerism
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CH3CH2CH2CH2CH3
C5H12
a) Chain/skeletal isomerism
The isomers differ in the carbon skeleton
(different carbon chain).
They possess the same functional group andbelong to the same homologous series.
Example:
CH3CHCH2CH3
CH3
CH3CCH3
CH3
CH3
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2)Positional isomerism
These isomers have a substituent group/ functional
group in different positions.Examples
C3H7Cl
CH3CH2CH2Cl1-chloropropane
2-chloropropane
CH3CHCH3
Cl
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C4H8
C8H10
CH3
CH
CH3
CH3
1,2-dimethylbenzene 1,3-dimethylbenzene
1-butene 2-butene
CH2=CHCH2CH3 CH3CH=CHCH3
CH3
C H 3
1,4-dimethylbenzene
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C6H13N
CH3
H N
CH2NH2
CH3
NH2
CH3
NH
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3)Functional group isomerism
These isomers have different functional groups and
belong to different homologous series with the samegeneral formula.
Different classes of compounds that exhibit
functional group isomerism :-
General formula Classes of compounds
CnH2n+2O ; n > 1 alcohol and ether
CnH2nO ; n 3 aldehyde and ketone
CnH2nO2; n 2 carboxylic acid and ester
CnH
2n; n 3 alkene and cycloalkane
E l
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Examples
C2H6O
C3H6O
C3H6O2
CH3CCH3 CH3CH2CH
CH3COCH3CH3
CH2
COH
O
ethanoldimethyl ether
propanalpropanone
propanoic acid methyl ethanoate
CH3CH2OH CH3OCH3
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Exercise:
1. State how many are isomers with the following molecularformulae, identify the type of isomerism and draw the
structural formula of the isomers.
a) C5H10
b) C5H10O2
c) CH3CH=C(Cl)CH3
d) C4H6Cl2
e) CH3CH2CH(OH)CH(Br)CH2CH3
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Lecture 5
12.4 IsomerismLearning Outcomes:
At the end of the lesson the students shouldbe able to :
Define stereoisomerism.
Describe cis-trans isomerism due torestricted rotation about C=C bond and CC
bond in cyclic compounds
Identify cis-trans isomerism of a givenstructural formula.
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Stereoisomerism / optical isomerism :
Isomerism that resulting from differentspatial arrangement of atoms
in molecules.
Two subdivisions of stereoisomers:i) Enantiomers (mirror image)
ii) Diastereomers (non-mirror image)
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Diastereomer
Cis-Trans Isomerism
The requirements for geometric isomerism
:i) restricted rotation about a C=C,double
bond in alkenes, or a C-C single bondin cyclic compounds.
ii) each carbon atom of a site of restrictedrotation has two different groupsattached to it.
E l
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Examples
C C
CH3H
H3CC C
CH3H3C
H
H
CH
H
CH
trans-2-butene cis-2-butene
cis-1,2-dimethylcyclohexane
trans-1,2-dimethylcyclohexane
CH3
CH3
H
H
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If one of the doubly bonded carbons has 2 identical
groups, geometric isomerism is not possible.
Example
No cistrans isomer
C C
CH3H3C
H3C
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Lecture 6
12.4 IsomerismLearning Outcomes:At the end of the lesson the students should be able to:
Identify cis-trans isomerism of a given structural
formula. Define chirality centre and enantiomers.
Identify chirality centre in a molecule.
Explain optical activity of a compound.
Draw a pair of enantiomers using 3-dimensionalformula.
Define racemate.
State the applications of chiral compounds in daily
life.
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Optical I somerism Optically active compounds have the ability to
rotate plane-polarized light to the right
(dextrorotary) and to the left (levorotary)
The angle of rotation can be measured with an
instrument called polarimeter.
Enantiomer
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Polarimeter
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The requirements for optical isomerism :-
i) molecule contains a chiral carbon or chirality centre
or stereogenic centre (a sp3
-hybridized carbon atomwith 4 different groups attached to it)
ii) molecule is not superimposable with its mirror
image.
P
CQ
R
S*
PQRS*designates chiral centre
Enantiomers
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Enantiomers
a pair of mirror-image that are not superimposable.
Example:-
i) 2-butanol ,
C*
CH2CH3
H3C
OHH
C
CH2CH3
CH3HOH
CH3CHCH2CH3
enantiomers
ii) 2 hydroxypropanoic acid
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ii) 2-hydroxypropanoic acid,
enantiomers
COOH
HO H
CH
COOH
H OH
CH3
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12.4.9 Racemate
A racemic mixtureorracemate isan
equimolar mixture of enantiomers which is
optically inactive because the two componentsrotate plane-polarized light equally (same
degree of rotation) but in opposite directions.
Hence it does not give a net rotation of plane-
polarized light.
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Applications of chiral compounds in
daily life.e.g:
() Dopa is used for treatment of Parkinsons
disease but (+) dopa is toxic to human. (S)-Ibuprofen the popular analgesic(the active
ingredient in motrin, advil, and many other
nonaspirin analgesics)
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REACTIONS OF ORGANIC
COMPOUNDS
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Lecture 7
12.5 Reactions of Organic Compounds
Learning Outcomes:
At the end of the lesson the students should
be able to :Explain covalent bond cleavage:
homolytic
heterolytic
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Types of Covalent Bond Cleavage/F ission
All chemical reactions involved bond
breaking and bond making.
Two types of covalent bond cleavage :-
Homolytic cleavage
Heterolytic cleavage
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a) Homolytic Cleavage
Occurs in a non-polar bond involving two
atoms of similar electronegativity.
A single bond breaks symmetrically into
two equal parts, leaving each atom with one
unpaired electron.
Formed free radicals.
Example:
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X : X
Example:
X + X
free radicals
X X
b) Heterolytic cleavage
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b) Heterolytic cleavage
Occurs in a polar bond involving unequal sharing of
electron pair between two atoms of differentelectronegativities.
A single bond breaks unsymmetrically.
Both the bonding electrons are transferred to the moreelectronegative atom.
Formed cation and anion.
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A is moreelectronegative.
B is more
electronegative.
A:- + B+anion cation
A : B
A+ + B:-cation anion
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Reaction I ntermediates
a) Carbocation
b) Carbanion
c) F ree Radical
They are unstable and highly reactive.
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a) Carbocation
Also called carbonium ion.
A very reactive species with a positive
charge on a carbon atom.Carbocation is formed in heterolyticcleavage.
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Example :
(CH3)3CCl (CH3)3C
+ + Cl-
carbocation anion
Chlorine is more electronegative than carbon and the
CCl bond is polar.
The CCl bond breaks heterolitically and both the
bonding electrons are transferred to chlorine atom to
form anion and carbocation.
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b) Carbanion
is an anion counterpart
a species with a negative charge on a carbonatom.
Carbanion is formed in heterolytic cleavage.
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example:
(CH3)3CLi (CH3)3C- +Li+ carbanion
kation
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b) F ree Radical
A very reactive species with an unpaired electron.
Formed in homolytic cleavage.
Examples:
i)
free radicals
Cl
Cl uv Cl
+ Cl
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C C C + C
H3C H H3CH+
ii)
iii)
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Lecture 7
12.5 Reactions of Organic Compounds
Learning Outcomes:
At the end of the lesson the students should beable to:
State the relative stabilities of primary, secondaryand tertiary free radicals, carbocations andcarbanions.
Explain the inductive effect of alkyl grouptowards the stability of carbocations andcarbanions.
Define electrophile and nucleophile.
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Relative Stabil i ties of Carbocations,
Carbanions and F ree Radicals
Carbocation, carbanion and free radical
can be classified into:
Primary
Secondary
Tertiary
Carbocat ion Stabi l i ty
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The alkyl groups (electron-releasing group)stabilise the positive charge on the
carbocation.
The stability of carbocation increases with the
number of alkyl groups present.
Carbocat ion Stabi l i ty
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Carbocation Stabil i ty:
H
C HH+
R
C RH+
R
C RR+
H
C RH+
<