Organic Chemistry is the study of Carbon and its compounds.
Organic compounds are compounds containing Carbon, hydrogen and any one or two other elements like Sulphur, Nitrogen, Oxygen, Phosphorus and even metals like Sodium and potassium.
General Properties of Organic Compounds
1.The solid ones have low melting and low boiling points.
2. They are soluble in non-polar solvents.
3. They are thermally unstable ( i.e easily decompose/ breakdown on heating)
4. They combustible
5. They are mostly covalent in nature.
HYDROCARBONS
Hydrocarbons are compounds containing only two elements, that is, Hydrogen and Carbon.
There are three main families of hydrocarbons
****The Alkanes
****The Alkenes and
****The Alkynes
Sources of hydrocarbons
There are three main sources of hydrocarbons,
i. Crude oil or petroleum
ii. Natural gas
iii. Coal
I. Crude oil/petroleum: - Crude oil is a viscous dark liquid that is found in deposits underground. It is formed from animal remains and marine vegetation, algae e.t.c when these are subjected to pressure, heat and bacterial activity they gradually change to this dark viscous liquid known as crude oil.
Crude oil exploration and drilling
Crude oil-bearing rocks and areas are located and explored by the following processes.
I. Taking an aerial photograph of the place.
II. Examining and testing the surface rocks.
III. Drilling large holes/core into the ground
IV. Exploding dynamite in the deep holes drilled into the earth's crust taking recordings and reflections of shock waves resulting from the explosions in the rocks.
ii. Natural gas: - Natural gas is a naturally occurring hydrocarbon mixture composed mainly of methane (CH4 about 65% -90%)). Along with methane are other hydrocarbons like ethane, propane and butane.
It is formed from the decomposition and compression of organic matter, like dead plants and animals, over thousands of years and is usually found in deep underground deposits.
It is extracted from these underground deposits (reservoirs) by drilling pipes into the reservoirs. It is then separated and purified into its various components by fractional distillation.
Uses
i. it is used mainly for heating as fuel,
ii. it is used for generating electricity
iii. it used as fuel for transportation in the form of liquified natural gas
Even though we consider natural gas as a relatively clean fossil fuel, its extraction, transportation and various uses can still affect our environment (such as water pollution, methane emissions and land disturbance).
Coal: - Coal is a solid fossil fuel that is mainly composed of carbon, as well as various amounts of other elements such as hydrogen, oxygen, sulfur, and nitrogen (see carbon and its compounds)
Fractional Distillation Of Petroleum
Unless it is refined, crude oil will just be a viscous liguid with very limited use. But when it undergoes fractional Distillation, it is separated into various compounds.
Fractions from fractional Distillation of Petroleum
Table: -showing various petroleum fractions and their uses
Fractions | Number of C-atoms | Uses | |
1. | Petroleum gas | C1 - C4 | Used mainly as fuel and manufacturing of other organic compounds like chloromethane |
2. | Ether | C4 – C6 | Used as solvents |
3. | Petrol | C7 -C10 | Used mainly as fuel for motor car engines |
4 | Kerosene | C10 – C18 | Fuel for cooking, for lighting and used for jet engines |
5 | Diesel oil | C18 – C25 | It is used as a raw material for cracking process, used as fuel for diesel engines |
6 | Lubricating oils | C20 – C35 | Used for i. oiling / lubricating moving parts of machines, engines and generators ii. Raw material for making candles, hair cream and body creams products |
7. | Bitumen | Above C35 | Used for road construction |
Classification of Hydrocarbons
Hydrocarbons are classified into
I. Aliphatic and
II. Aromatic Hydrocarbons
ALIPHATIC HYDROCARBONS: - These are straight chain, branched chain or cyclic hydrocarbons that are saturated or unsaturated.
Examples of aliphatic hydrocarbons are (CH3CH2CH3) propane, (CH3CH2CH=CH2) butane, pentyne
AROMATIC HYDROCARBON: - These are hydrocarbons that contain the benzene ring (C6H6) in its structure. Aromatic Hydrocarbons are unsaturated.
ALIPHATIC HYDROCARBONS: - these are straight chain, branched chain or cyclic hydrocarbons that are saturated or unsaturated.
Examples of aliphatic hydrocarbons are (CH3CH2CH3) propane, (CH3CH2CH=CH2) butene, CH3CH2CH2C≡CH) pentyne, CH3CH2CH2C≡CH)
Straight Chain hydrocarbons H H H ׀ ׀ ׀ H – C – C – C −H ׀ ׀ ׀ H H H Propane |
H H H ׀ ׀ ׀ H−C – C – C= C– H ׀ ׀ ׀ H H H Butene
|
H H H ׀ ׀ ׀ H – C – C– C –C ≡ C –H ׀ ׀ ׀ H H H Pentyne |
Branched chain hydrocarbon
H H H ׀ ׀ ׀ H− C – C – C −H ׀ ׀ H H H – C – H ׀ H
2-methyl propane |
| Cyclic hydrocarbon H ׀ C ∕ \ H − C − C – H Cyclopropane |
AROMATIC HYDROCARBON: - These are hydrocarbons that contain the benzene ring (C6H6) in its structure. Aromatic Hydrocarbons are unsaturated.
Terminologies in Organic Chemistry.
I. CATENATION- this is the ability of an element to form single and multiple bonds with itself and other elements.
2. OCTANE NUMBER: - This is the measurement of the efficiency of combustion of petrol in car engines.
It is based on the proportion of branched chain alkanes to straight chains in a given fuel.
For instance, a sample of petrol that contains a high proportion of normal (straight chain) heptane than 2,2,4 trimethylpentane has a low octane number of below 50.
3. HYBRIDIZATION: - This is the mixing of orbitals to get the same number of hybrid orbitals.
4. HOMOLOGOUS SERIES: - This is a family of organic compounds that conforms to a general molecular formular, and successive members differs by a -CH2- group.
Examples of homologous series include the alkanes, alkenes and alkynes
Characteristics of a Homologous Series
i. Members differs by a -CH2- group
. Members have the same general molecular formular
iii. Members have similar chemical properties
iv. Members have the same general method of preparation
v. There is a gradual change in the physical properties of members as you go down the group.
ALKYL GROUP: - This is a homologous series of hydrocarbons formed by the loss of a hydrogen atom by a corresponding alkane.
The following table shows the first five alkyl members and their corresponding alkane.
Alkyl group | Corresponding Alkane | Formula |
CH3 | CH4 | H ׀ H – C – ׀ H |
C2H5 | C2H6 | H H ׀ ׀ H – C – C – ׀ ׀ H H |
C3H7 | C3H8 | H H H ׀ ׀ ׀ H – C – C – C − ׀ ׀ ׀ H H H |
C4H9 | C4H10 | H H H H ׀ ׀ ׀ ׀ H – C – C – C – C − ׀ ׀ ׀ ׀ H H H H
|
C5H11 | C5H12 | H H H H H ׀ ׀ ׀ ׀ ׀ H – C – C – C – C – C − ׀ ׀ ׀ ׀ ׀ H H H H H |
The alkyl groups are generally represented by the letter R
FUNCTIONAL GROUP: - A functional group is an atom, a bond or a group of atoms that is present in all the members of a homologous series, and it determines the chemical properties of the family.
The table below shows some functional groups and their names as sufixes and prefixes
Functional groups | Name as Suffix | Name as Prefix |
−OH R-OH |
-Ol | Hydroxy- |
− COOH O ∕∕ — C ∖ H |
-Oic acid |
- |
−COOR O ∕ − C \ OR |
Alkanoate |
- |
− CONH2 O ∕ − C \ NH2 |
-amide |
- |
−C=O O ∕∕ −C \
|
-One |
-oxo- |
-CHO O ∕∕ −C \ H |
-al |
Oxo- |
−NH2 −N |
-amine
|
amino |
−CN −C≡N |
-carbonitrile |
cyano |
−Cl |
|
-Chloro |
−Br |
|
-bromo |
−I |
|
-iodo |
− |
-ane |
|
= |
-ene |
|
≡ |
-yne |
|
The three main hydrocarbons (that is, the alkane, the alkene and the alkyne are discussed separately in different posts.
OBJECTIVE QUESTIONS
1. Octane number is highest in petrol containing a high proportion of
a. heptane
b. octane
c. 2-methylpentane
d. 2,2,4-trimethylpentane
2. Compounds containing only hydrogen and carbon are called
a. hydrocarbons
b. alkanes
c. isomers
d. organic
3.
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