Lecture 5 Introduction to Organic Chemistry.ppt

Lecture 5: Introduction to Organic Chemistry – A Comprehensive Guide for Undergraduate Students
This PowerPoint presentation, Lecture 5: Introduction to Organic Chemistry, is an essential resource designed for undergraduate students pursuing chemistry, biology, pharmacy, and other science-related disciplines. It provides a structured and detailed introduction to the fundamental concepts of organic chemistry, ensuring a solid foundation for further studies in the field.

Organic chemistry is a crucial branch of chemistry that focuses on the structure, properties, composition, reactions, and synthesis of carbon-containing compounds. It plays a pivotal role in various scientific fields, including medicine, pharmaceuticals, biochemistry, environmental science, and materials science. This lecture presentation covers the core principles necessary to understand organic molecules and their transformations, making it an invaluable tool for students and educators alike.

Key Topics Covered in this Lecture:
1. Introduction to Organic Chemistry
Definition and significance of organic chemistry in the scientific world.
Historical development of the field and major contributors.
The distinction between organic and inorganic compounds.
2. Structure and Bonding in Organic Compounds
Atomic structure and electronic configuration.
Covalent bonding and hybridization (sp, sp², sp³).
Molecular orbital theory and resonance structures.
The concept of electronegativity and polarity in organic molecules.
3. Functional Groups and Their Importance
Overview of key functional groups: alkanes, alkenes, alkynes, alcohols, ethers, aldehydes, ketones, carboxylic acids, esters, amines, amides, and aromatic compounds.
How functional groups determine the chemical properties and reactivity of organic molecules.
The role of functional groups in biological and industrial applications.
4. Nomenclature of Organic Compounds
Systematic IUPAC naming conventions for aliphatic and aromatic compounds.
Common names vs. IUPAC names.
Rules for naming branched-chain hydrocarbons, cyclic compounds, and complex organic molecules.
5. Isomerism: The Different Forms of Organic Molecules
Structural isomerism: Chain, positional, and functional group isomers.
Stereoisomerism: Geometrical (cis-trans) and optical isomerism.
Chirality and enantiomers in biological systems.
6. Reaction Mechanisms in Organic Chemistry
Introduction to reaction mechanisms and their importance in predicting product formation.
Classification of organic reactions:
Substitution reactions (SN1, SN2)
Addition reactions (electrophilic and nucleophilic addition)
Elimination reactions (E1, E2 mechanisms)
Rearrangement reactions
Oxidation and reduction reactions in organic synthesis
The role of catalysts and reaction conditions in determining reaction outcomes.
7. Organic Chemistry in Everyday Life
The impact of organic chemistry on medicine and drug development.
The significance of polymers and plastics in modern materials.

1. Introduction to Organic Introduction to Organic
ChemistryChemistry
Lecturer:
Chemistry section
MUST
February, 2017

2. What is Organic ChemistryWhat is Organic Chemistry
•A branch of chemistry that deals with the study of the chemistry of
carbon compounds also known as organic compounds.
•Organic chemistry is the study of compounds containing carbon and
chiefly or ultimately of biological origin.
•Why is carbon dedicated a branch of chemistry
–Carbon is one of the elements that form a wide range of
compounds.

3. Why Carbon Forms Millions of CompoundsWhy Carbon Forms Millions of Compounds
Carbon is the element that by itself, forms
more compounds than all the other elements
put together.
•Carbon forms four stable covalent bonds. It forms stable bonds
with many atoms of other elements N, O, halogens, P and S
•Carbon can form bonds to itself, producing long stable chains
of carbon atoms (catenation). It also forms ring structures.
•Carbon can form single, double and even triple bonds.

4. Differentiating organic and inorganic Differentiating organic and inorganic
compounds todaycompounds today
Organic Compounds Inorganic Compounds
Use mostly covalent bondingMostly ionic bonding
Are gases, liquids or solids with
low melting points
Are generally solids with high
melting points
Mostly insoluble in water Many are water soluble
Many are soluble in organic
solvents such as petroleum,
benzene and hexane
Most are not soluble in organic
solvents
Solution in water generally do
not conduct electricity
When dissolved in water conducts
electrical current
Almost all burn Most not combustible
Slow to react with other
chemicals
Often undergo fast chemical
reactions

5. Classification of Organic CompoundsClassification of Organic Compounds
•To date over five million organic compounds are known
(discovered or synthesized).
•Classified into families according to the functional groups
they contain.
•Functional group: An atom or a group of atoms with
characteristic chemical and physical properties:
•A reactive part of the molecule that imparts the characteristic physical
and chemical properties of an organic compound.
There are many families of organic compounds which can be
broadly categorized as hydrocarbons, oxygen-containing
compounds and compounds containing nitrogen.

6. Hydrocarbons
Aliphatic Aromatic
AlkanesAlkenesAlkynesCyclic
Hydrocarbons:Hydrocarbons:
•contain only hydrogen and carbon
•Can be divided into different types,
depending on their bonding.

7. Hydrocarbons….Hydrocarbons….
•Alkanes: Carbon chain, no double or triple
bonds. All single bonds (saturated)
•Alkenes: Carbon chain, contains double
bond(s) (unsaturated)
•Alkynes: Carbon chain, contains triple bond(s)
(unsaturated)

8. Representing Organic CompoundsRepresenting Organic Compounds
•Chemists use several methods to
represent organic molecules and these
are
–molecular formula
–expanded structural formula,
–condensed structural formula
–bond-line formula

9. Representing Organic Compounds: Representing Organic Compounds:
Molecular FormulaMolecular Formula
•MF tells the kind and number of each type of atom in
a molecule
•It does not show how the atoms have been bonded
to each other.
•Example: the molecular formula of hexane is C
6H
14.
–This MF tells that hexane is composed of six carbon
atoms and fourteen hydrogen atoms.
–However it does not show the sequence of
bonding of these atoms.

10. Representing Organic Compounds: Expanded Representing Organic Compounds: Expanded
Structural FormulaStructural Formula
•The expanded structural formula shows all atoms in a molecule
and how they have been joined to each other.
•Chemists use a two-dimensional structural formula to show all
the atoms with all of their bonds in the plane of the page.
•Note: molecules are three-dimensional and the two-dimensional
structure is used for convenience.
•The expanded structural formula of hexane is:
Expanded structural formula
C C C
H
H
H
H
H
C
H
H
C
H
H H
C
H
H
H
H

11. Representing Organic Compounds: Representing Organic Compounds:
Condensed Structural FormulaCondensed Structural Formula
•Condensed structural formula: usually for molecules with large number of
atoms.
•Shows all the atoms in a molecule and placing them in a sequential order
that indicates bonding.
•The expanded structural formula of hexane can be condensed as

CH
3CH
2CH
2CH
2CH
2CH
3.
•Note that hexane has four repeating CH
2
 groups. The CH
2
 group is
called a methylene group.
•The methylene group can be written in parenthesis with the subscript
showing how many times the group is repeating.
•Therefore the condensed formula is CH
3
(CH
2
)
4
CH
3
.

12. Representing Organic Compounds: Bond- Representing Organic Compounds: Bond-
Line FormulaLine Formula
•The most preferred representation of molecules
•Easy to draw while conveying the essential information about the
structure of the molecule.
•A carbon atom is understood to be at every intersection of lines
and at the end of the line; hydrogen atoms are filled mentally.
The line formula of hexane is:
Line formula

13. AlkanesAlkanes
•Simplest of all: contain only carbon and hydrogen
atom with single bonds only.
•Since in alkanes, the carbon atom forms the
maximum number of possible single bonds, i.e.
four bonds, alkanes are said to be saturated.
•Can be straight-chain, branched-chain or cyclic
molecules.
•In straight-chained alkanes, the carbon atoms are bonded or linked
together in a linear fashion, one after another.
–Each carbon atom is bonded to two other carbon atoms and two
hydrogen atoms except the terminal (end) carbon atom which is
bonded to one other carbon atom and three hydrogen atoms

14. Examples of AlkanesExamples of Alkanes
Propane
CH
3
H
2
C
H
3C
Hexane
H
3C
H
2
C
C
H2
H
2
C
C
H2
CH
3
Some examples of Straight-chain alkanes
=
=
Butane
CH
3
C
H
2
H
2
C
CH
3
=
Cyclohexane
CH
2
C
H
2
H
2C
H
2C
H
2
C
CH
2
Cyclopentane
CH
2
CH
2
C
H
2
H
2C
H
2C
Examples of Cyclic alkanes

15. Alkenes and AlkynesAlkenes and Alkynes
•Alkenes contain only at least one carbon-
carbon double bond (CC) whereas alkynes
have a carbon-carbon triple bond (CC) .
•Alkenes and Alkynes are unsaturated because
they have fewer hydrogen atoms than
compounds with carbon–carbon single bonds.
•Unsaturated hydrocarbons react readily with
small diatomic molecules, such as hydrogen in
an addition reaction (TBD).

16. Examples of Alkenes and AlkynesExamples of Alkenes and Alkynes
Propene
1-butene
Examples Alkenes and their line formula
CH2
H
C
H3C H2C
C
H
H2
C
CH3
2-methy-2-pentene
CH3
C
C
H
H2
C
H3C CH3
But-2-ene
H3C
C
H
H
C
CH3
=
=
= =
Propyne
But-1-yne
Examples of Alkynes
HCCCH3
HC
C
C
H2
CH3
But-2-yne
H3CCCCH3

17. Aromatic hydrocarbons (Arenes)Aromatic hydrocarbons (Arenes)
•Aromatic compounds contain benzene rings in
their molecules.
•So named because the earliest known aromatic
compounds had strong characteristic Aroma
(odors).
•The simplest aromatic compound is called
benzene, molecular formula C
6
H
6
.

18. Aromatic hydrocarbons….Aromatic hydrocarbons….
•Describe the benzene ring structure
Benzene ring

19. Aromatic hydrocarbons….Aromatic hydrocarbons….
Benzenemethylbenzene
Aromatic Hydrocarbons
ethylbenzene
CH
3
H
2
C
CH
3

20. Naming HydrocarbonsNaming Hydrocarbons
•There's always a Prefix and a suffix
–prefix: # of carbons in main chain or ring
–suffix: Type of bonding in the chain or ring
(the class of organic compound)

21. PrefixesPrefixes
C atomsPrefixCarbon
atoms
Prefix C atomsPrefix
1 meth 11 undec 21 Henicos
2 eth12 dodec 22 Docos
3 prop12 tridec 23 Tricos
4 but14 tetradec 30 Triacont
5 pent15 pentadec 31 Hentriacont
6 hex16 hexadec 32 Dotriacont
7 hept17 octadec 40 Tetracont
8 oct18 nonadec 50 Pentacont
9 non19 nonadec 60 Hexacont
10 dec20 icos 100 Hecta

22. SuffixSuffix
•Alkane: -ane
•Alkenes: -ene
•Alkynes: -yne

23. Names of the first 10 straight-chain alkanes
C atoms Prefix alkane
1 meth methane
2 eth ethane
3 prop propane
4 but butane
5 pent pentane
6 hex hexane
7 hept heptane
8 oct octane
9 non nonane
10 dec decane

24. Alkyl groups and the symbol RAlkyl groups and the symbol R
•An alkyl group is obtained after removing one
hydrogen atom from an alkane.
–Unbranched alkane with a hydrogen atom removed from
the terminal, or end, carbon.
•To name the alkyl group, you replace the suffix ane from the
name of the unbranched alkane with yl. For example if you take
away one hydrogen atom from methane (CH
4
), it becomes CH
3
,
and the name changes from methane to methyl.
Alkane Name Alkyl Group Name
CH
3
CH
2
H ethane CH
3
CH
2
 ethyl
CH
3CH
2CH
2H propane CH
3CH
2CH
2 Propyl
CH
3
CH
2
CH
2
CH
2
H butane CH
3
CH
2
CH
2
CH
2
butyl

25. Alkyl groups and the symbol R…
•The symbol R represents an alkyl group.
•A methyl group,
•An ethyl group
•A propyl group.
•etc
•For example, the general formula for an alkane is
RH. The R group can be a methyl in a methane
molecule or an ethyl in an ethane molecule.

26. “Normal” v. Branched hydrocarbons
•“Normal” hydrocarbons are straight chains; no branching
•Branched-chain hydrocarbons: isomers of “normal”
hydrocarbons; have same formula, but different structures
•‘Branched-chain alkanes have many different possible
structures.
•The IUPAC Rules of Nomenclature also make it possible
for you to distinguish between the many different
structures

27. General IUPAC Rules for Naming
hydrocarbons
1. Identify the type of hydrocarbon and choose the correct suffix: -ane
for alkanes, -ene, for alkenes, or –yne for alkynes
2. Determine the longest carbon chain.
–If the hydrocarbon is an alkene or an alkyne, choose the longest chain that
includes the carbon-carbon double bond for alkenes or triple bond for alkynes.
–If the hydrocarbon is an alicyclic, the longest chain starts and stops within the
cyclic structure.
3. Assign numbers to each C of the parent chain.
For alkenes and alkynes the first carbon of the multiple bonds
should have the smallest number.
For branched-chain alkanes the first should have the lowest
number (locant). Carbons in a multiple bond must be ,
numbered consecutively.

28. IUPAC Rules for Naming
hydrocarbons…..
4. Attach a prefix that corresponds to the number of carbons in the
parent chain.
Add cyclo- to the prefix if it is a cyclic structure.
5. For branched-chain hydrocarbons, determine the correct name for
each branch (“alkyl” groups include methyl, ethyl, propyl, etc.)
If the hydrocarbon has two or more different branches, then
attach the name of the branches alphabetically, along with
their carbon position, to the front of the parent chain name.
Separate numbers from letters with hyphens (e.g. 4-ethyl-2-
methyldecane)
6. When two or more branches are identical, use prefixes (di-, tri-,
etc.) (e.g. 2, 4-dimethylhexane). Numbers are separated with
commas.

29. IUPAC Rules for Naming
hydrocarbons…..
•Prefixes are ignored when determining alphabetical
order.
–i.e. the prefixes are not part of the branch name when
listing the branched in alphabetical order, they just indicate
the number of branches of that particular type (e.g. 2,3,5-
trimethyl-4-propylheptane)
•When identical groups are on the same carbon, repeat
the number of this carbon in the name.(e.g. 2,2-
dimethylhexane)

30. Nomenclature of branched chain alkanes
2-methyl pentaane
CH
3
CH
C
H
2
H
2
C
CH
3 CH
3
CH
3
CH
C
H
2
H
2
C
CH
3 CH
3
substituent
CH
3
CH
C
H2
H
2
C
CH
3 CH
3
1
2
3
4
5
CH
3
CH
C
H
2
H
2
C
CH
3 CH
3
5
4
3
2
1

31. Nomenclature of branched chain alkanes
2,4-dimethylhexane
2
3
4
5
6
1
2
3
4
5
6
1
2,3,3-trimethylhexane
2,3,5-trimethyl-4-propylheptane
2
3
4
5
6
7 1

32. IUPAC Rules for alkenes and alkynes
•The IUPAC nomenclature rules for alkenes and alkynes
are similar to those of alkanes.
•The following is the summary of steps you follow
when naming these unsaturated hydrocarbons:
–Count the carbon atoms to find the longest continuous chain
that contains the multiple bond. Name the parent compound
by adding suffix –ene for an alkene and –yne for an alkyne.
For example:
ethene ethynepropene propyne
CH2CH2 CHCHCH2C
H
CH3 CHCCH3

33. IUPAC Rules for alkenes and
alkynes.........
•Number the carbons in the parent chain in such a way that the
carbon atoms forming the multiple bonds have the lowest possible
numbers.
•In the older IUPAC rules the number indicating the position of the
double or triple bond was placed in front of the parent name with
a hyphen.
•Under the newer rules, this number is placed in between the prefix
and suffix and is separated with hyphens.
2-hexyne (old)
hex-2-yne (new)
1-hexene (old)
hex-1-ene (new)
1
2
3
4
5
6
1
2
3
4
5
6

34. IUPAC Rules for alkenes and
alkynes.............
•If the carbon-carbon double or triple bond is at an equal distance
from both ends of the parent chain, then begin numbering from
the end that is nearest to the first branch.
6
5
4
3
2
1
1
2
3
4
5
6
7 7
and not
6
5
4
3
2
1
1
2
3
4
5
6
8 77 8
and not

35. IUPAC Rules for alkenes and
alkynes.............
•Assign numbers and names to the branching
substituents, and list the substituents alphabetically. Use
commas to separate numbers and hyphens to separate
words from numbers.
6
5
4
3
2
1
87
6
5
4
3
2
1
7
2-methylhex-3-ene 2,4-dimethylhex-3-ene

36. IUPAC Rules for alkenes and
alkynes.............
•If more than one multiple bond is present, identify the
position of each multiple bond and use the appropriate
ending -diene, -triene, -tetraene etc. for alkenes and
diyne, triyne, tetrayne etc. for alkynes.
6
5
4
3
2
1
87
6
5
4
3
2
1
7
2,4-dimethylhexa-1,3-diene
2-methylhexa-2,3-diene
6
5
4
3
2
1
hexa-1,4-diyne

37. IUPAC Rules for alkenes and
alkynes.............
•For cyclic alkenes or alkynes, number the carbon atoms in the ring
in such a way that the double or triple bond is in between carbon
atoms 1 and 2, and number in the direction about the ring so that
the substituents have the lowest possible numbers. For example:
2
1
6
5
4
3
1-methylcyclohex-1-enecyclohexene
1
2
3
4
5
6
3-methylcyclohex-1-ene
1
2
3
4
5
6
2,3-dimethylcyclohex-1-ene
2
1
6
5
4
3

38. Nomenclature of Aromatic
Hydrocarbons.............
•All aromatic hydrocarbons are based on the benzene. Consequently when
naming aromatic hydrocarbons you use ‘benzene’ as the parent name.
•For example, methyl benzene
•In this case, there is no need to indicate the position of the substituent
group as there is only one: all positions are considered equivalent.
•However, when you have two or more groups attached to the ring you
use numbers to indicate the positions of the groups.
•You do this by numbering the carbon atoms of the ring starting from one
of the carbons where one group is attached, making sure you have the
lowest numbers as possible. For example consider the following arenes:
CH3

39. Nomenclature of Aromatic
Hydrocarbons.............
•You do this by numbering the carbon atoms of the ring
starting from one of the carbons where one group is
attached, making sure you have the lowest numbers as
possible:
•For example,
CH3
CH3 CH3CH3
CH3
CH3
A B C
1
2
1
2
3
1
2
3
4

40. Nomenclature of Aromatic
Hydrocarbons.............
•Alternatively, whenever there are two substituents, they can be
named by the common nomenclature using ortho (o-), meta
(m-) or para (p-) (1-4 placement). Ortho, meta and para
correspond to 1-2, 1-3 and 1-4 positions.
•For example,
CH3
CH3 CH3CH3
CH3
CH3
o-dimethylbenzenem-dimethylbenzene
p-dimethylbenzene
1
2
1
2
3
1
2
3
4
CH3
CH2CH3
1
2
3
4
p-ethylmethylbenzene

41. Nomenclature of Aromatic Hydrocarbons
using benzene as substituent
•In some aromatic hydrocarbons, benzene is considered as a
substituent (side chain).
•This is when the alkyl group (saturated chain) attached to the
benzene has more than six carbon atoms and when the benzene is
attached to unsaturated chain (alkene or alkyne chain).
•In such compounds the aromatic group, C
6H
5 is named as a
phenyl group abbreviated as Ph.
•For example:
2-phenylheptane
CH3
H
C
H2
C
C
H2
H2
C
C
H2
CH3
2-phenyl-2-butene
CH3
C
H
C
CH3