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TAMPINES JUNIOR COLLEGE
2014 JC1 Chemistry
H2 Level - Introduction to Organic Chemistry
Lecture Outline:
1.
2
Introduction
1.1
Formulae of Organic Compounds
1.2
Functional Groups
1.3
Homologous Series
1.4
Systematic Naming of Organic Compounds
1.5
IUPAC Rules
1.6
Hybridisation of Carbon Atom
1.7
Concept of Sigma () Bond and Pi () Bond
1.8
Shapes and Bond Angles of Organic Molecules
Isomers
2.1
Isomerism
2.2
Formula for Determining the Number of Stereoisomers
2.3
Biological Properties of Stereoisomers
References:
1) Chemistry in Context by Hill & Holman
2) Understanding Advanced Organic and Analytical Chemistry by Chan & Tan
3) Principle Of Organic Chemistry/2nd Edition /Pg 14-23 by Peter R.S. Murray
TPJC/H2 Chem/Intro Organic Chem Part 1/ 1
Learning Objectives (9647 Syllabus)
At the end of this series of lectures, you should be able to:
(a)
interpret, and use the nomenclature, empirical, molecular, structural, skeletal and
displayed formulae of the following classes of compound:
(i)
alkanes, alkenes and arenes
(ii)
halogenoalkanes and halogenoarenes
(iii)
alcohols (including primary, secondary and tertiary) and phenols
(iv)
aldehydes and ketones
(v)
carboxylic acids, acyl chlorides and esters
(vi)
amines, amides, amino acids and nitriles
(b)
interpret, and use the following terminology associated with organic reactions:
(i)
functional group
(ii)
homolytic and heterolytic fission
Will be
(iii)
free radical, initiation, propagation, termination
covered in
the other
(iv)
nucleophile, electrophile
sub-topics
(v)
addition, substitution, elimination, hydrolysis
(vi)
oxidation and reduction
[in equations for organic redox reactions, the symbols [O] and [H] are acceptable]
(c)
describe sp3 hybridisation, as in ethane molecule, sp2 hybridisation, as in ethene and
benzene molecules, and sp hybridisation, as in ethyne molecule
(d)
explain the shapes of, and bond angles in, the ethane, ethene, benzene, and ethyne
molecules in relation to σ and π carbon-carbon bonds
(e)
predict the shapes of, and bond angles in, molecules analogous to those in (d)
(f)
describe structural isomerism
(g)
describe geometrical isomerism in alkenes, and explain its origin in terms of restricted
rotation due to the presence of π bonds [use of E, Z nomenclature is not required]
(h)
explain what is meant by a chiral centre
(i)
deduce whether a given molecule is optically active based on the presence or absence of
chiral centres and/or a plane of symmetry
(j)
recognize that optical isomers have identical physical properties except in the direction in
which they rotate plane-polarised light
(k)
recognize that optical isomers have identical chemical properties except in their
interactions with another chiral molecule
(l)
recognize that different stereoisomers exhibit different biological properties, for example in
drug action
(m) deduce the possible isomers for an organic molecule of known molecular formula
(n)
identify chiral centres and/or geometrical isomerism in a molecule of given structural
formula
TPJC/H2 Chem/Intro Organic Chem Part 1/ 2
Part 1: Introduction
1.0
Introduction

What is Organic Chemistry ?
Organic chemistry is the chemistry of

__________ compounds
The word ‘Organic’ , originally used to relate carbon compounds which were
obtained from living organisms;

Organic Compounds : urea ( H2N-C-NH2 ), starch (C6H10O5)n
ll
proteins, fatty acids .....
O

1.1
Non-organic / Inorganic compounds : CO32 , SCN , CN , CO ....
Formulae of Organic Compounds
Objective: Candidates should be able to:
(a) interpret, and use the nomenclature, empirical, molecular, structural, skeletal and displayed formulae of
the following classes of compound: alkanes, alkenes and arenes, halogenoalkanes and
halogenoarenes, alcohols (including primary, secondary and tertiary) and phenols, aldehydes and
ketones, carboxylic acids, acyl chlorides and esters, amines, amides, amino acids and nitriles
In candidates’ answers, an acceptable response to a request for a structural formula will be to give the
minimal detail, using conventional groups, for an unambiguous structure, e.g. CH 3CH2CH2OH for propan-1ol, not C3H7OH.
i.
Empirical formula:
Formula which shows the
whole number ratio of atoms of different
elements in the compound. e.g. glucose, ( CH2O )
ii.
Molecular formula:
Formula which shows the
number of atoms of each elements present in
the compound. e.g. glucose, ( C 6H12O6 )
iii.
Structural formula:
Formula which shows
e.g. ethanol, CH3CH2OH
iv.
atoms in the molecule are joined together.
Displayed formula:
Formula which shows both the relative placing / ______________
of atoms and the number of bonds between them
e.g. ethane , C2H6
H
covalent bonds in the molecule must be shown.

It’s a 2-D Flat diagrams in which the bond angles are not what they seem,
HCH =109.5 O not 90 O .

Two exceptions of acceptable displayed formulae are:
H
H
C
C
H
H
and
benzene or aromatic ring
cyclohexane ring
TPJC/H2 Chem/Intro Organic Chem Part 1/ 3
H
v.
Stetreo-chemical formula (3-D) :
C
Structural formula which indicates the orientation of the atoms
in space and the shape of the molecule

109.5 O
3-D Wedge diagrams
Indicates bonds _____________ the plane of the paper
Indicates bonds ______________________the plane of the paper
Indicates bonds ________________the plane of the paper
vi.
Skeletal formula:
represents pentane ( a 5-C alkane)
represents butanol ( a 4-C alcohol)
OH
1.2
Functional Group
Objective: Candidates should be able to:
(b) interpret, and use the following terminology associated with organic reactions: functional group
Functional group refers to the part / portion of the organic molecule that is
chemically reactive or more reactive which governs the principal chemical
properties of the series or class of organic compounds.
e.g

CH3─CH2 ─OH
Alkanes and benzene molecules contain no specific portion of the molecule
that is more reactive. Every part of the molecule is similar in reactivity.
H
methane
, CH4
C
H
H
H
H
benzene
H
H
≡
H

Note that all C- H bonds are identical!
H
H
TPJC/H2 Chem/Intro Organic Chem Part 1/ 4
1.3
Homologous Series ( H. S.)
Homologous series refers to a series of compounds in which each
member differs from the next by a constant amount of ______units (-CH2-).
Each member is called a homolog.
Homologous Series of Alkane Family ( C1  C10 )
Table-1.1 :
Molecular
formula
CH4
C2 H6
C3 H8
C4H10
C5H12
C6H14
C7H16
C8H18
C9H20
C10H22
IUPAC
Prefix
methethpropbutpenthexheptoctnondec-
IUPAC
name
methane
ethane
propane
butane
pentane
hexane
heptane
octane
nonane
decane
nth member
nth member
CH4
CH3CH3
CH3CH2CH3
CH3CH2CH2CH3
CH3CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH3
CH3CH2CH3CH2CH2CH2CH2CH2
CH3CH2CH2CH2CH2CH2CH2CH2CH3
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
General formula: CnH2n+2
Table-1.2
Molecular
formula
CH3-OH
C2H5-OH
C3H7-OH
C4H9-OH
C5H11-OH
C6H13-OH
C7H15-OH
C8H17-OH
C9H19-OH
C10H21-OH
Structural
formula
The Homologous Series of Alcohols ( C 1  C10 )
IUPAC
Prefix
methethpropbutpenthexheptoctnondec-
IUPAC
name
methanol
ethanol
propanol
butanol
pentanol
hexanol
heptanol
octanol
nonanol
decanol
Structural
formula
CH3-OH
CH3CH2-OH
CH3CH2CH2-OH
CH3CH2CH2CH2-OH
CH3CH2CH2CH2CH2-OH
CH3CH2CH2CH2CH2CH2-OH
CH3CH2CH2CH2CH2CH2CH2-OH
CH3CH2CH2CH2CH2CH2CH2CH2-OH
CH3CH2CH2CH2CH2CH2CH2CH2CH2-OH
CH3CH2CH2CH2CH2CH2CH2CH2CH2CH2-OH
General formula: CnH2n+2O
(or CnH2n+1OH )
TPJC/H2 Chem/Intro Organic Chem Part 1/ 5
Table-1.3 Some Common Functional Groups (A-level Course)
(Refer to Annex 1 for more details Pg 24-25)
1.3.1
Special Features of Some important functional Groups
A.
Hydrocarbon C
H
1.
e.g
H
Alkane C with
C
All C-H bonds are similar. Non-reactive C.
H
H
2.
3. *
H
C
e.g
single bonds , tetrahedral shape;
H
C
H
Alkene C , with
single +
double bonds,
trigonal planar shape; Very reactive C.
H
Bezene C , with 2 single +1 double bonds,
e.g
trigonal planar shape; unreactive benzene ring.
Benzene ring showing delocalized -bonds
*
= actual structure of benzene ring with delocalized -bond
(This structure should be drawn in the A level syllabus)
B.
4.
Hydroxy Compounds
e.g
C
Alcohol C with
shape;
OH
single bonds , tetrahedral
O-H is the reactive functional group.
5. *
e.g
OH
Phenolic C , with 2 single +1 double bonds,
trigonal planar shape.
Both -OH and benzene ring are reactive.
Phenol with benzene ring showing delocalized -bonds
*
OH = actual structure of phenol with benzene ring with delocalised -bond
(This structure should be drawn in the A level syllabus)
TPJC/H2 Chem/Intro Organic Chem Part 1/ 6
C.
6.
Compounds with Carbonyl group
R
`
e.g
C
O
Aldehyde
H
`
7.
R’
`
e.g
C
R
`
HO
`X
e.g
1.4
C
O
C
Ketone
O
O
H
`
R’
O
R
`
8.
C
C
O
R
`
Carboxylic acid
C
O
HO
`X
Systematic Naming (Nomenclature) Of Alkanes & Other Organic
Compounds

IUPAC = International Union of Pure & Applied Chemistry


Used for compounds even with complicated structures.
Systematic naming of organic compounds generally have these components:
prefix
parent stem
suffix

prefix indicates the number, name and position of the substituents

parent stem specifies the number of C-atom in the longest C-chain.

suffix indicates the homologous series (functional group) the molecule
belongs to (refer to Table 1.3 in the Annex for nomenclature).
e.g
1
2
3
4
5
6
CH3CHCH2CH2CH2 CH3
CH3
Prefix
parent stem
2-methyl
suffix
-ane
-ene
-one
hex
Suffix
ane
homologous series
alkanes
alkenes
ketones
TPJC/H2 Chem/Intro Organic Chem Part 1/ 7
1.5
IUPAC Rules (Systematic Nomenclature):
To name a compound with branched or otherwise substituted chain, these steps are
followed:
a)
Identify the longest chain of carbon atoms & assign the parent name of the
compound from the number of carbons.
CH3CHCH2CHCH2 CH2CH3
e.g. 1
CH2CH3
CH3
longest C-chain =
parent name is ______________
e.g. 2
CH3CHCH2CHCH2CH3
CH2 CH2CH3
CH3
longest C-chain =
parent name is ______________
b)
Number the parent chain beginning at the end which will result in the lowest
possible numbers for the substituents attached to the chain.
7
6
5
4
3
2
1
1
2
3
4
5
6
7
CH3CHCH2CH CH2 CH2CH3
CH3
CH2CH3
Substituent alkyl groups at positions 2 & 4 not 4 & 6.
c)
Name each substituent and indicate its position by the number of the carbon
to which it is attached.
1
2 3
4 5
6
7
CH3CHCH2CHCH2 CH2CH3
CH3
CH2CH3
IUPAC name :
TPJC/H2 Chem/Intro Organic Chem Part 1/ 8
d)
If the parent chain is substituted by the same group more than once, the number
of these identical groups is indicated by the prefixes di , tri , tetra and so forth.
Br
Br
H
C
C
CH3
H
CH3
IUPAC name :
e)
If there are two or more substituents, they are named in their alphabetic order.
Br
e.g
1
2
3
4
CH2CH2CH2 CBr
Cl
5 CHCH3
6 CH3
IUPAC name :
1.6
Hybridization Theory :
Objective: Candidates should be able to:
(c)
(e)
describe sp3 hybridisation, as in ethane molecule, sp 2 hybridisation, as in ethene and benzene
molecules, and sp hybridisation, as in ethyne molecule
predict the shapes of, and bond angles in, molecules analogous to those in (d)
Table 1.6.1: Summary of Shapes and Bond Angles of Organic Molecules
Ethane, C2H6
Ethene, C2H4
Benzene, C6H6
Ethyne, C2H2
H
Shape of molecule and
type of hybrid orbital of
each C atom
H
H
C H
H
C H
H
Tetrahedral
H
around each
(sp3)
Bond angles
Hybridization around C
Atomic orbitals of each C atom
used in mixing
No. of  bonds
= No. of hybrid orbitals of each C
atom
No. of  bonds = No. of p orbitals
of each C atom not involved in
hybridisation
Total no. of  and  bonds in
molecule
H
H
C C
H
H
H
C
C
C
C
C
C
H
H
H
Trigonal
planar around
each C atom
(sp2)
Trigonal
planar around
each C atom
(sp2)
H
C
C
Linear around
each C atom
(sp)
109.5
sp3
s, p, p, p
120
sp2
s, p, p
180
sp
s, p
4
3
2
0
1
2
7
0
5
1
12 
3
3
2
TPJC/H2 Chem/Intro Organic Chem Part 1/ 9
H
1.7 Theory of Hybridization of Carbon
Chemical Data of Carbon:

Symbol , C

Atomic no. = 6

Group IV element

Valency of 4

Ground state electronic configuration, 1s 2 2s2 2p2

Ground state electronic configuration:
 Full electronic configuration:
( show spins of electrons and empty orbitals )
1s2

1s
2s2
2p2



2s
2px
2py 2pz
Hybridization Process
2 step process :
 Step-1: Excitation State
 Step-2: Hybridization or Mixing of orbitals
Step 1: Excitation State
To form four covalent bonds, one electron has to be promoted from the nearest 2s to
an empty 2p orbital:

C* (excited state)




(electronic configuration)
1s
2s
2px 2py 2pz
Step 2 :`Mixing` of Orbitals
‘Mixing’ or hybridization of valence shell orbitals takes place at the
excited state which gives rise to the following 3 possible outcomes.
1st outcome:

2s
+
Mixing of (one s and three p) orbitals

2px


FOUR identical sp3orbitals
2py 2pz
TPJC/H2 Chem/Intro Organic Chem Part 1/ 10
109.5
O
Fig. 7 (i)
2nd outcome:


+
2s
Mixing of (one s and two p) orbitals
2px


THREE sp2identical orbitals
2py 2pz
(and one unhybridized porbital)
p
Fig. 7 (ii)
sp2
sp2
1200
sp2
3rd outcome:

+
Mixing of (one s and one p) orbitals



2px
2py 2pz
TWO spidentical orbitals
(and two unhybridized porbitals)
2s
y
z
Fig. 7 (iii)
p
sp
sp
p
sp
X
TPJC/H2 Chem/Intro Organic Chem Part 1/ 11
1.7.1
Formation of Carbon-Hydrogen Single Bonds
Objective: Candidates should be able to:
(d) explain the shapes of, and bond angles in, the ethane, ethene, benzene, and ethyne molecules
in relation to σ and π carbon-carbon bonds
 -bond formation ( end to end overlapping )
Fig 7.1(a)
S
sp3– s overlapping
≡ -bond
sp3
sp3
sp3
S
S
sp3
S
H
sp3-s
 -bond
sp3-s
 -bond
H
Fig 7.1(b)
sp3-s
e.g CH4, methane
1.7.2
C
H
sp3-s
 -bond
H
 -bond
Formation of Carbon-Carbon Double Bonds
Fig 7.2(a) -bond formation
side to side p-p overlapping of orbitals
-bond
p
sp2
sp2
sp2
e.g
H2CCH2, ethene
TPJC/H2 Chem/Intro Organic Chem Part 1/ 12
Fig 7.2(b)
H
H
sp2 – sp2,

CC


C
p – p, 


H
H
1.7.3
Formation of Carbon-Carbon Triple Bonds
e.g
HC≡CH, ethyne
Fig 7.3(a)
H
s-sp
p –p, 
sp–sp, 
p –p, 
CC

sp-s
C

H
Checkpoint 1
State the type of hybridization of the carbon atoms, labeled 1 to 5, in the following
molecule and hence the geometry (shape) about each of them.
1
5
3
4
2
----- End of Part 1 -----TPJC/H2 Chem/Intro Organic Chem Part 1/ 13