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Nov 1, 2018

Alkenes or Olifins

Alkenes or Olifins:

Unsaturated Compounds:

The compounds contains at least one pair of adjacent carbon atoms linked by a multiple bond, then that compound is said to be unsaturated.
Examples:
1.Ethylene(C₂H₄): 
This Compound contain a double bond. There are only four univalent hydrogen atoms present in ethylene, therefore ethylene said to be unsaturated Compound.
Alkene Formula and Name Naming of Alkanes.
Structure Of Ethylene

2.Acetylene(C₂H₂): 
This Compound contain a triple bond and there are only two univalent hydrogen atoms.
Alkene Formula and Name Naming of Alkanes.
Structure of Acetylene

Alkenes or Olefins:

The alkenes are the unsaturated hydrocarbons that contain one double bond. They have the general formula CnH2n, as they contain two hydrogen atoms less than the alkanes, alkenes are called unsaturated hydrocarbons. The double bond is called 'olifinic'bond or 'ethylenic bond'.
The name olefin arose from the fact that ethylene was called 'olefiant gas'( oil-forming gas), since it forms oily liquids when treated with chlorine or bromine. The original name given to this homologous series was olefine, but it was latter decided to reserve the suffix -ine for basic substances only. 

Nomenclature of Alkenes or Olifins: 

1.Common naming system of Alkenes or Olifins:

In the common naming system of an olefin is named according to the following rules,

Alkene Formula and Name Naming of Alkanes.
Some Simple Alkenes or Olifins with Their Common and IUPAC Names
1. The total number of carbon atom in the olefin is counted and the name of the corresponding alkane is determined.

CH₂ = CH₂  Corresponding alkane is ethane.
2. By changing the name of the corresponding alkane, the suffix -ane of the latter into -ylene.

CH₂ = CH₂  To change the suffix of corresponding alkane.
CH₂ = CH₂ → ethane → ethylene
3.The position of the double bond is indicated by Number, 1,2,3,4...., or Greek Letters, α, β, ⋎, ઠ, ...., the end carbon atom nearest to the double bond is denoted by 1, next 2,and so on or α, next β, and so on. These letters are then known as locants.
Alkene Formula and Name Naming of Alkanes.
Position of Double Bond
 3. The locants of the double bond carbon atom is then placed before the name of the olifin as obtain from rule 1 and 2. A hyphen is written in between the locants and the name. The locants are used only to name olefins containing more then three carbon atom.

Olifins of low molecular weights only have common names.

Examples:
1. CH₃ - CH = CH₂
Parent alkane is propane
Thus the name of the Compound is 1 - propylene or α - propylene
2. CH₃ - CH₂ - CH = CH₂
Parent alkane is butane
Thus the name of the Compound is 1 - butylene or α - butylene
3. CH₃ - CHCH - CH₃
Parent alkane is butane
Thus the name of the Compound is 2 - butylene or β butylene
Write down the common names of the following compounds:
(i) CH₂CH₂CH₂CH=CH₂ (ii) CH₃CH=CHCH₂CH₃.
(i) CH₂CH₂CH₂CH=CH₂
Parent alkane is pentane
Thus the name of the Compound is 1 - pentylene or α - pentylene.
(ii) CH₃CH=CHCH₂CH₃
Parent alkane is pentane
Thus the name of the Compound is 2 - pentylene or β pentylene 

2.Substituted or Derived Nomenclature: 

Another method of nomenclature is to consider ethylene as the parent substance and higher member is derivatives of ethylene.
If the compound is mono-substituted then no difficulty arises in naming.
But the compound is a di- substituted derivatives of ethylene isomerism is possible. Since the alkyl groups are of attached same or different carbon atoms.
When the groups are attache to the same carbon atom of the olifins named as the the asymmetrical compound.
When the groups are attache to the different carbon atom of the olifins named as the the symmetrical compound.

Examples:

1. CH₃CH = CH₂
Methylethylene
2. CH₃ㄧCH₂CH = CH₂
Ethylethylene
3. CH₃ ㄧ(H₃C)C = CH₂
as - dimetylethylene
4. CH₃CH = CHCH₃
sym - dimethylethylene

3. I.U.P.A.C. System of Nomenclature:

According to the I.U.P.A.C. system of nomenclature, the class suffix of the olifins is ene, and so the series becomes the alkene series.
1.The longest carbon chain containing the double bond is chosen as the parent alkene.

Example:  

CH₃C(CH₃)₂CH₂CH(CH₃)CH=C(C₂H₅)CH₂CH₃
Alkene Formula and Name Naming of Alkanes.
Longest Carbon Chain



The parent part is here base chain, it consists of 8 carbons. The base name, therefore, is to be derived from octane.
2. The position of the double bond and side chains are indicated by numbers, the lowest number possible being given to the double bond, and this is placed before the suffix.
Alkene Formula and Name Naming of Alkanes.
Position of the Double Bond



To give the lowest number possible double bonded carbon is numbered 3.
3. The name of which is obtained by changing the suffix - ane of the corresponding alkane into - ene
There are four branches
one ethyl branch on carbon atom number 3, three methyl branches on 5th and 7th carbon atoms. These are to be indicated as prefixes to the base name. 
Their names with their locants are, 3 - ethyl - 5, 7, 7 - trimethyl.
Hence the full name is 3 - ethyl - 5, 7, 7 - trimethyl - 3 - octene.
The I.U.P.A.C. system is now the one generally used.
What are the names of the following compounds in the IUPAC system ?
(i) CH₃ - CH₂ - CH = CH₂ (ii) C(CH₃)₂ = CH₂
(iii) CH₃ - CH = C(CH₃) - CH₂ - CH₃
(iv) CH₂ = C(C₂H₅) - CH(CH₃)₂
Alkene Formula and Name Naming of Alkanes.
but - 1- ene
Alkene Formula and Name Naming of Alkanes.
2 -methylprop - 1 - ene

Alkene Formula and Name Naming of Alkanes.
3 - methylpent - 2 - ene
Alkene Formula and Name Naming of Alkanes.
2 - ethyl - 3 - methylbut - 1 - ene