Organic chemistry
Organic Chemistry
• Organic means living
• Hydrocarbons contain hydrogen and carbon
atoms
• Organic Chemistry is the study of carbon
chemicals that are natural and artificial.
• The bonding in hydrocarbons is covalent so
bonding between molecules is weak.
• The structure is molecular.
Homologous series
This is a series of compounds which all contain the same
functional group, and have similar chemical properties.
ALKANES
ALKENES
ALCOHOLS
CH4
CH2 =CH2
CH3OH
CH3-CH3
CH2 =CH –CH3
CH3CH2OH
Each has a general formula:
ALKANES: CnH2n+2
The members of the series differ by the number of CH2
units.
CH3-CH3, CH3-CH2-CH3, CH3-CH2-CH2-CH3
Graduation in physical properties: eg: boiling points.
CH4 (GAS), C8H18 (LIQUID), C30H62 (SOLID)
IUPAC
The International Union of Pure and
Applied Chemistry
Why?
Historical names (e.g. acetic acid,
formic acid) meant nothing to other
scientists in different countries
IUPAC Rules for Alkane
Nomenclature
1. Find and name the longest continuous carbon
chain. AKA parent chain
2. Identify and name groups attached to this
chain.
3. Number the chain consecutively, starting at the
end nearest a substituent group.
4. Designate the location of each substituent
group by an appropriate number and name.
5. Assemble the name, listing groups in
alphabetical order.
The prefixes di, tri, tetra etc., used to designate
several groups of the same kind, are not considered
when alphabetizing.
Naming Alkanes
• General formula CnH2n+2
• Saturated compounds: each carbon is bonded
to the maximum possible number of atoms.
“Prefix + Root + Suffix”
• Find the main chain (1 = meth, 2 = eth, 3 =
prop, 4 = but, 5 = pent, 6=hex)
• Determine your suffix (Alkane = ane)
• Number the main chain. Start at the end that
gives branches the lowest numbers.
• Name each branch as an alkyl group (methyl,
ethyl, propyl etc.), and placing a position
number in front.
• Note: always put commas between numbers,
and hyphens between numbers and letters.
ALKANES
SATURATED HYDROCARBONS – contain maximum
amount of hydrogen - only single bonds (no multiple
bonds)
NAMING ALKANES
No of C
atoms
Prefix
1
Meth
2
Eth
3
Prop
4
But
5
Pent
6
Hex
7
Hept
8
Oct
All alkanes end
with ‘ANE’.
All belong to the same
HOMOLOGOUS series
GENERAL FORMULA
CnH(2n+2)
Examples:
H
H
C
Methane CH4
H
H
H
H
Ethane C2H6
H
C
C
H
H
H
Alkyl Groups
Branches on carbon chains
H
H
C
CH3
methyl
H
H
10
H
H
C
C
H
H
CH2CH3
ethyl
Name these molecules
3-ethyl-3,4-dimethylhexane
STRUCTURES OF ALKANES
METHANE CH4
Bond Angle
109.5o
Shape
Tetrahedral
H
Can be illustrated as:
H
C
H
H
ETHANE.
Molecular formula C2H6
Structural formula: CH3 CH3
or
H
H
H
C
C
H
H
H
PROPANE.
Molecular formula: C3H8
Structural formula: CH3 CH2 CH3 or
Both ethane and propane are
“straight” chain molecules
BUT!!
H
H
H
H C
C
C
H
H
H
H
Bonds are NOT 90o molecules are NOT STRAIGHT!!!
Schematic formula
Give the names of the following alkanes
(a) CH3 CH2
CH
CH2 CH3
CH3
(b) CH3 CH
CH3
CH2
CH
CH3
CH3
(c) CH3 C(CH3)2 CH2 CH(CH3) CH2 CH3
(d) CH3CH2CH(CH3)C(CH3)3
Give the names of the following alkanes
(a) CH3 CH2
CH
CH2 CH3
3-methyl pentane
CH
2,4-dimethylpentane
CH3
(b) CH3 CH
CH3
CH2
CH3
CH3
(c) CH3 C(CH3)2 CH2 CH(CH3) CH2 CH3 2,2,4-trimethyl
hexane
(d) CH3CH2CH(CH3)C(CH3)3 2,2,3-trimethylpentane

Cyclic Alkanes
When C atoms bond together to form a ‘ring’ – known as
a ‘cyclic’ structure.
Example
What is the molecular
formula of this alkane?
How does the molecular
formula compare to the
general formula for alkanes?
Why does it belong to the
series of alkanes?
Can you think of a name
for this molecule
CYCLOHEXANE
Illustrate the cyclic
structures of (a) C4H8 and
(b) C5H10 and name the
molecules.
Commas and dashes
• Use commas between numbers
• Use dashes between numbers and letters
• And one other thing; when arranging your
substituent groups in alphabetical order
the di, tri, tetra, etc do not count
Correct the mistakes
You have 1 minute to discuss with a
partner all the mistakes in the naming
of the following compounds
H3C
Cl
Cl
C
C
CH3
Br
CH2
CH3
Name A:
4-methyl-3-4-dichloro-3-bromo-pentane
Name B:
3-bromo-3,4-dichloro-4-methyl-pentane
3-bromo-2,3-dichloro-2-methylpentane
Key
Incorrect number
Cl
Cl
1
H3C
C
2
CH3
3
C
Br
4
CH2
Dash or comma
5
CH3
Name A:
4-methyl-3-4-dichloro-3-bromo-pentane
Not alphabetical
Name B:
3-bromo-3,4-dichloro-4-methyl-pentane
Worked example 1
1 2
2
1
3
3
6
4
5
1. 6 carbons in the longest chain
 hexane
2. has 2 chloro- groups 
dichloro
Has a methane group  methyl
3. Number the chain (see diagram)
4. 1,2-dichloro4-methyl
5. 1,2-dichloro-4-methylhexane
Remember: when arranging your
substituent groups in alphabetical
order the di, tri, tetra, etc do not
count
Isomers
 Same
molecular formula
 Same
number and types of atoms
 Different
23
arrangement of atoms
Examples of Isomers
The formula C4H10 has two different structures
CH3
CH3CH2CH2CH3
Butane
CH3CHCH3
2-methylpropane
When a CH3 is is used to form a branch, it makes a new
isomer of C4H10.
24
Structural Isomers
 Compounds
pp
that have the same
molecular formula, but different
molecular structures, are called
structural isomers
 Butane and 2-methylpropane on
previous slide.
 Also have different properties, such
as b.p., m.p., and reactivity
25
Geometric Isomers
pp
 There
is a lack of rotation around a
carbon to carbon multiple bond
– has an important structural implication
– Two possible methyl arrangements:
1. trans configuration - substituted
groups on opposite sides of double
bond
2. cis configuration - same side
26
Geometric Isomers
 Differ
pp
only in the geometry of their
substituted groups
 Like other structural isomers, have
different physical and chemical
properties
27
Geometric Isomers of 1,2-dichloroethene
 Cl
Cl
H
C=C
H
Cl
C=C
H
Cl
H
cis
trans
 Rigid structure so these are
isomers with different properties.
28
Geometric Isomers of chloroethene? pp
H
Cl
H
C=C
H
 Rigid
H
C=C
H
H
Cl
structure BUT both carbons
do NOT have two DIFFERENT
groups attached to them.
 These are just rotated in space, but
are the same.
29
Nongeometric versions of 1,2-dichloroeth”ene”
 Cl
Cl
H
C--C
H
 Non-rigid
Cl
C--C
H
Cl
H
structure so these are
NOT isomers. (The 3rd hydrogen
on each carbon is not shown)
30
pp
BUTANE & ISOMERS.
Molecular formula: C4H10 - can have two different
structures
“Straight” chain. CH3 CH2 CH2 CH3
BUTANE
Schematic formula:
Branched chain CH3 CH
CH3
CH3
METHYL PROPANE
branch
Isomers
Compounds that have the same molecular formula but
different structural formula.
TASK:
Illustrate the structures of the three different
isomers of C5H12.
Names & Structures
Examples
CH3
2- methylbutane
CH3 CH CH2 CH3
CH3
CH3 C
CH3
2,2 – dimethyl propane
CH3
TASK: illustrate the structures of:
2-methylpentane.
CH3CH(CH3)CH2CH2CH3
2,3 – dimethylbutane.
CH3CH(CH3)CH(CH3)CH3
2,2,3 -trimethylpentane CH3C(CH3)2CH(CH3)CH2CH3
Alkenes
•
•
•
•
CnH2n
A by-product of CRACKING an Alkane
Used for making polymers
C=C is more reactive than C-C
The molecule is unsaturated and the double
bonds allow addition polymerisation.
H
H
C
H
C
H
Ethene C2H4
Structure of Alkenes
The shape around the double bond is planar.
The bond angle around the double bond is 120o
PLANAR
Represented as

C bond

C
C
C
120o
Examples of Alkenes
………………, C2H4
H
H
C
H
PROPENE
OR …………………….
C
H
CH2
CH
CH3
TASK: Use ball & stick models or sketches to construct and name 3
different structures for C4H8 each one with one double bond.
Examples of Alkenes
H
ETHENE, C2H4
H
C
H
H
C
PROPENE
C
H
H
OR CH2 CH2
C
H
CH2
CH
CH3
CH3
TASK: Use ball & stick models or sketches to construct and name 3
different structures for C4H8 each one with one double bond.
CH3CH2CH
CH3CH
CH2 BUT-1-ENE
CHCH3
BUT-2-ENE
CH3C
CH2 METHYL
PROPENE
CH3
More Alkenes
Illustrate structures of the following alkenes:
Pent-1-ene
Hex-3-ene
2-methylbut-1-ene
Cyclohexene
Name the following alkenes
CH3CH
CH2
CHCH2CH3
CHCH(CH3)CH2CH3
CH3CH(CH3)CH
(CH3)3CCH
CHCH2CH3
C(CH3)2
More Alkenes
Illustrate structures of the following alkenes:
Pent-1-ene
CH2 CHCH2CH2CH3
Hex-3-ene
CH3CH2CH CHCH2CH3
2-methylbut-1-ene
CH2 C(CH3)CH2CH3
Cyclohexene
Name the following alkenes
CH3CH
CH2
CHCH2CH3
CHCH(CH3)CH2CH3
CH3CH(CH3)CH
(CH3)3CCH
Pent-2-ene
3-methylpent-1-ene
CHCH2CH3
C(CH3)2
2-methylhex-3-ene
2,4,4-trimethylpent-2-ene
GEOMETRIC ISOMERS
 There is no rotation about the double bond.
GEOMETRIC ISOMERISM each C atom in the double bond has two
different atoms/groups attached.
BUT–2-ENE CH3 CH CH CH3
CH3
C
H
CH3
C
H
cis but-2-ene
CH3
C
H
C
H
CH3
trans but-2-ene
Geometric isomerism is a form of STEREOISOMERISM –
Same molecular and structural formula but atoms are arranged
differently in space
Alkynes
H-C≡C-H
Ethyne
H-C≡C-CH3
propyne
H-C≡C-CH2-CH3
But–1-yne
CH3-C≡C-CH3
But–2-yne
Very reactive
Triple bond unstable!
Attracts electrophiles.