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Friday, 19 April 2024

HYDROCARBONS at a glance

Organic Chemistry is the study of Carbon and it's 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 solids 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. The are mostly covalent in nature.

              HYDROCARBONS
Hydrocarbons are compounds containing only two elements, that is, Hydrogen and Carbon.

Sources of hydrocarbons

There are three main sources of hydrocarbons, and they are.
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 vegetations, 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 then separate 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,  CH3CH2CH2C≡CH) 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,


 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

benzene

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.

 This is the main reason why so many organic compounds exist, in fact, we have thousands of organic compounds. And these compounds are grouped into families known as homologous series.

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 formulary 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 post. 




 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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