Chapter 1 introduction to organic chemistry

1. FHSC1124
Organic Chemistry
Introduction to Organic
Chemistry
Chapter 1

2. Chapter Scopes
•Introduction
•Homologous series
•Functional groups
•Naming/Nomenclature
•Isomerisms

3. Objectives
After this chapter, you will:
•Learn and differentiate functional
groups
•Learn to name organic compounds
according to IUPAC nomenclature
and draw correct structure
•Learn about types of isomerism

4. Introduction to Organic Chemistry

5. Introduction to Organic Chemistry
•Organic compounds are classified into
different types, such as alkanes, alkenes,
alcohols, amines and etc.
•Each type of organic compound contains
the same reactive group of atoms, which is
called functional group.
 E.g. alcohols contain the –OH functional
group

6. Functional Groups
Functional Group Structure
Alkane
Alkene (Olefin) C=C (ethylenic bond)
Alkyne CºC (acetylenic bond)
Alcohol (hydroxyl)
Arenes (aromatic
hydrocarbon)
Ar (Aryl)
Aldehyde
R – H
O
R – C – H
R – O – H

7. Functional Group Structure
Ketone
Carboxylic Acid (carboxyl)
Ester
O
R – C – R’
O
R – C – OH
O
R – C – O – R’

8. Functional Group Structure
Anhydride
Amide
Amine
Nitrile
O O
R – C – O – C – R’
O
R – C – NH
2

R – NH
2

9. IUPAC Nomenclature
•IUPAC ¾ International Union of Pure &
Applied Chemistry
•The IUPAC nomenclature system is a set
of logical rules devised and used by
organic chemists to name the organic
compounds.

10. IUPAC Rules
1.Select the longest continuous C chain as
parent chain (use root word for the no. of C)
2.Name each of the branch/substituents as an
alkyl / aryl group
3.Number the C chain begin from the end
nearest to the branch
Þ branch/substituents appear at the lowest
no. possible

11. 4.Name each substituent according to its
chemical identity & the no. of the C atom
to which it is attached
Þ For identical substituent, use the prefix
di, tri… & write appropriate C no. for each
substituent
5.Separate no. from no. by commas (,) & no.
from letters by hyphens (-)
6.List the substituents alphabetically by
name Þ di, tri…. don’t count

12. Functional Group Nomenclature
Alkane End with -ane
Alkene End with –ene
Arene End with –benzene
Alcohol End with –ol
Aldehyde End with –al
Ketone End with –one
IUPAC Nomenclature

13. Functional Group Nomenclature
Carboxylic acidEnd with –oic acid
Ester End with –oat
Anhydride End with –oic anhydride
Amine End with –amine
Amide End with –amide
Nitrile End with –nitrile

14. PrefixNo. of
Carbons (n)
Prefix No. of
Carbons (n)
Meth 1 Hex 6
Eth 2 Hept 7
Prop 3 Oct 8
But 4 Non 9
Pent 5 Dec 10
Base Names

15. Straight-Chain Alkyl Groups, R
Alkyl group Name (abbreviation)
-CH
3
Methyl (Me)
-CH
2
CH
3
Ethyl (Et)
-CH
2
CH
2
CH
3
Propyl (Pr)
-CH
2
CH
2
CH
2
CH
3
Butyl (Bu)
-CH
2
CH
2
CH
2
CH
2
CH
3
Pentyl
•Alkyl groups are named by replacing the
–ane ending of the parent alkane with an
–yl ending

16. Naming of Identical
Branch Substituents
No. of substituents Prefix
2 Di
3 Tri
4 Tetra

17. Isomerism
Definition of isomerism:
•A phenomena where 2 or more
compounds have the same molecular
formulae but with different arrangements
of their constituent atoms
•Such molecules are known as isomers

18. Isomerism
Isomerism
Structural
Isomerism
Stereoisomerism
Chain Isomerism
Position Isomerism
Functional Group Isomerism
Optical
Isomerism
Geometric
Isomerism

19. Structural Isomerism
•Isomers have the same molecular formulae
but different structural formulae
1.Chain Isomerism
•The isomers are from the same homologous
series & have the same functional groups but
different type of carbon chain.
•Example: C
4
H
10

20. 2. Position Isomerism
•The isomers are from the same
homologous series & have the same
functional groups but the position / location
of the functional group is different
•Same C skeleton
•Example: C
3H
8O

21. 3. Functional Group Isomerism
•The isomers are from different homologous
series & have different functional groups
•The chemical & physical properties are
different
•Example: C
3
H
6
O

22. Geometric Isomerism
(Cis-trans Isomerism)
•The atoms making up the isomers are
joined up in the same order, but manage to
have a different spatial arrangement.
•Due to restricted rotation of groups in
double bonds & in cyclic compounds.

23. Example: Geometric Isomerism
CC
Cl
Cl
H
H
trans-1,2-dichloroethene
CC
Cl
H
Cl
H
cis-1,2-dichloroethene
•trans isomer - 2 chlorine atoms are locked
on opposite sides of the double bond
(trans : Latin meaning "across“)
•cis isomer - 2 chlorine atoms are locked
on the same side of the double bond
(cis : Latin meaning "on this side")

25. The Effect of Geometric Isomerism
on Physical Properties
1.cis isomer has higher boiling point.
•Bp depends on the polarity of the molecules
•cis isomers are > polar, stronger attractive
intermolecular forces exist between cis
isomer
2.trans isomer has higher melting point.
•Mp depends on the arrangement & packing
of molecules in the crystal lattice
•trans isomer with > symmetrical structure,
can be > closely packed in the crystal lattice

26. ?? Cis-isomer has higher bp
•e.g. 1,2-dichloroethene
•1 side will be more positive charge & the
other side more negative Þ polar
•Van der Waals + dipole-dipole interaction
•Need extra energy Þ bp increases

27. ?? Trans-isomer has lower bp
•the slight charge on the top of the molecule
is exactly balanced by an equivalent
charge on the bottom
•No dipole-dipole force as it is non-polar
molecule.
•Thus, only held by weak Van der Waals
•Less energy needed Þ lower bp

28. ?? Trans-isomer has lower bp
•Trans-isomer
•No dipole-dipole force as it is non-polar
molecule.
•Thus, only held by weak Van der Waals
•Less energy needed Þ lower bp

29. ?? Trans-isomer has higher mp
•trans isomer has the higher melting point
Melting point = solid Þ solution
•In order for the intermolecular forces to
work well, the molecules must be able to
pack together efficiently in the solid.
•Trans isomers pack better than cis
isomers. The "U" shape of the cis isomer
doesn't pack as well as the straighter
shape of the trans isomer.

30. ?? Cis-isomer has lower mp
•The poorer packing in the cis isomers
means that the intermolecular forces aren't
as effective be
•Less energy is needed Þ mp lower

31. Optical Isomerism
•Optical isomers are 2 compounds with the
same structural formulae, but one isomer
is the mirror image of the other & cannot
be superimposed on one another in any
orientation
•It occurs when 4 different groups of atoms
are joined to a C atom by 4 single covalent
bonds.

32. Optical Isomerism
•Occurs because of the tetrahedral bonding
around a C atom
•Structures that can exist as 2 optical
isomers are said to be optically active &
possess a chiral centre
•Simple substances which show optical
isomerism exist as two isomers known as
enantiomers
•Chiral centre = atom bond with the 4
different groups, which is normally marked
with an asterisk (*)

33. Example: Optical Isomerism
Chiral
centre

34. Example: Optical Isomerism
•It is important this
time to draw the
COOH group
backwards in the
mirror image.
Incorrect

35. Exercise
For each of the following molecules, draw the
possible stereoisomers and state the type of
stereoisomers shown.
(a) C
6
H
5
CH=CHCOOH
(b) C
6
H
5
-CH(Cl)-CH=CH
2
(c) CH
3
CH=CHCH
3
(d) CH
3CH
2CH(NH
2)COOH

36. Summary
use IUPAC nomenclature to name and
draw correct structure of simple organic
compounds with different functional
groups.
Differentiate types of isomerism and draw
isomers.