Organic chem

1. Alkanes

2. Objectives
Sources of hydrocarbons
Uses of the fractions of crude oil
Reactions of alkanes
-combustion
-cracking
- halogenation
Drawing and naming alkanes

3. Hydrocarbons
Organic compounds made of only carbon
and hydrogen
The homologous series which are
hydrocarbons are alkanes and alkenes

4. Natural Sources of Hydrocarbons
 Crude oil or
petroleum –yellow or
black oily liquid. It is a
mixture of several
alkanes and alkenes
 Natural gas-
colourless. Mainly
consists of methane ,
with small amounts of
ethane, propane and
butane

5. Fractional Distillation of crude oil- How it
is extracted
 Crude oil is heated to 400⁰C and
the liquid and vapor are carried to a
fractionating tower
 The vapors rise through the bubble
caps and trays
 Most volatile components do not
condense and are collected at the
top of the tower
 Less volatile rise to their highest
point, they concedense on the
bubble cap and are collected in the
tray and tapped off at various levels
 The least volatile, bitumen, remains
in the bottom of the tower and is
tapped off.

6. Fractions collected in the column

7. Table Showing Fraction, Boiling point
range and use
Fraction Boiling point
range
Number of
carbons
Use
Refinery gas >25 1-4 Fuel for domestic use
Petrol(gasoline) 25-170 5-10 Fuel for internal combustion engines eg cars,
trucks. As solvents
Kerosene
oil(paraffin oil)
170-250 10-14 Fuel for cooking, heatings, jets
Diesel oil 250-350 14-20 Fuel in diesel engines eg cars and trucks
Fuel oil, lubricating
oil and waxes
350-400 18-30 Used as fuels in factories, boilers, ships,
powerstations. Lubricants for machinery parts.
Waxes- polishing waxes,wax paper, candles,
peroleum jelly
Bitumen >400 >30 Road surfacing. Roofing

8. Alkanes
Hydrocarbons with the general formula ,
CnH2n+2.
Their functional group is C-C
They are described as saturated as they
have no multiple bonds

9. Reactions of alkanes
 Combustion: Burn
with a blue,
smokeless flame to
produce CO2 and H2O
 Reaction is highly
exothermic
 Where there is a
scarity of oxygen the
products are CO and
H2O

10. Reactions of alkanes
 Cracking- breaking
down of large
hydrocarbons in to
smaller more useful
alkanes and alkenes
with the aid of heat
and/or catalyst
 C4H10 (g) → C3H6 (g) + CH4 (g)
 C4H10 (g) → C2H6 (g) + C2H4 (g)

11. Reactions of alkanes with halogens
 Alkanes only react with
halogens in the presence
of sunlight to form the
haloalkanes.
 This type of reaction is a
substitution reaction
 A hydrogen of the alkane
is replaced by a halogen
atom
 Hydrogen halide is
always produced

12. Rules for drawing and naming alkanes
 Identify the functional group and hence the suffix
 Identify the longest carbon chain and state the
prefix
 Identify any substituents( non hydrogen atom)
assign them locant numbers so they have their
lowest number
 Substiutents are named in alphabetic order
 If there is more than one of a particular atom,
then use the refic di/ tri and write the locant
number before the name

13. Drawing and naming alkanes
Number of C in
chain
Prefix
1 Meth-
2 Eth-
3 Prop-
4 But-
5 Pent-
6 Hex-
7 Hept-
8 Oct-
9 Non-
10 Dec-
Substituent Name of
substiuent
CH3 Methyl
C2H5 Ethyl
CnH2n+1 Alkyl
Cl- Chloro-
Br- Bromo-
I- Iodo-

14. Examples of names
 Func,grp- C-C ( -ane)
 Longest continuous
chain- 4 ( but-)
 Substituents :0
 Name : n-butane
 Func. Gp :C-C (-ane)
 Longest chain : 4( but-)
 Substituent- CH3 (methyl)
 Position of substituent :2
 Name : 2 –methylbutane