Priyam Study Centre

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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.
Unsaturated Hydrocarbon
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.
H2C = CH2
2.Acetylene(C2H2):
This Compound contain a triple bond and there are only two univalent hydrogen atoms.
HC CH

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,
1. The total number of carbon atom in the olefin is counted and the name of the corresponding alkane is determined.
H2C=CH2 
Corresponding alkane is ethane.
2. By changing the name of the corresponding alkane, the suffix -ane of the latter into -ylene.
Alkenes H2C=CH2
Corresponding alkane ethane
Name of the Alkene ethylene
3.The position of the double bond is indicated by Number 1, 2, 3, 4...., or Greek Letters α, β, , , ...., 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.
  2 1
CH3 CH = CH2
3   2 1
CH3 CH2 CH = CH2
3   2 1
CH2 CH = CH CH2
  β ɑ
CH3 CH = CH2
ɣ   β ɑ
CH3 CH2 CH = CH2
ɣ   β ɑ
CH2 CH = CH CH2
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.
  2 1
CH3 CH = CH2
Parent alkane is propane
Thus the name of the Compound is
1 - propylene
or α - propylene
1. CH3 - CH2 - CH = CH2
1 - butylene
or 
α - butylene
2. CH3 - CH = CH - CH3 
2 - butylene 
or β - butylene

Write down the common names of the following compounds:
(i) CH3CH2CH2CH=CH2 (ii) CH3CH=CHCH2CH3.

(i) CH3CH2CH2CH=CH2
3   2 1
CH3 CH2 CH2 CH = 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
Formula Structural Formula Common Name
C4H8 (CH3)2C=CH2 isobutylene
C5H10 CH3CH2CH2C=CH2 ɑ-pentylene
or,
ɑ-amylene
C5H10 CH3CH=CHCH2CH3 β-pentylene
or,
β-amylene
C5H10 (CH3)2C=CHCH3 isopentylene
or,
isoamylene
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.
1. CH3CH = CH2 
Methylethylene 
2. CH3ㄧCH2CH = CH2
Ethylethylene
3. CH3 ㄧ(H3C)C = CH2
as - dimetylethylene
4. CH3CH = CHㄧCH3
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.
CH3C(CH3)2CH2CH(CH3)CH=C(CH3)CH2CH3
CH3 CH CH = C CH3

CH2
CH2
CH3 C CH3
CH3

CH3
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.
5 4 3
CH3 CH CH = C CH3
6 CH2 2 CH2
CH3 C CH31 CH3
8 CH3
To give the lowest number possible double bonded carbon is numbered 3. 
The name of which is obtained by changing the suffix - ane of the corresponding alkane into - ene.
There are four branches:
 
 
One methyl 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,  5, 7, 7 - trimethyl
Hence the full name is,
3, 5, 7, 7 - tetramethyl - 3 - octene

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

(i) CH3 - CH2 - CH = CH2 
but-1-ene 
(ii) C(CH3)2 = CH2 
2-methylprop-1-ene 
(iii) CH3 - CH = C(CH3) - CH2 - CH3
3-methylpent-2-ene
(iv) CH2 = C(C2H5) - CH(CH3)2
2-ethyl-3-methylbut-1-ene

Write out the (ignoring stereo-chemistry) of the isomeric pentenes, and name them by the IUPAC system. Give the structures of the products formed from each on Ozonolysis.

The Molecular formula of the pentene is C5H12.
Now take each one in turn and introduce one double bond, starting at the least substituted end and shifting the double bond inwards.
(i) CH3CH2CH2CH=CH2
pent-1-ene 
(ii) CH3CH2CH=CHCH3
pent-2-ene
(iii) CH3CH(CH3)CH=CH2
3-methylbut-1-ene
(iv) CH3C(CH3)=CHCH3
2-methylbut-2-ene
(iv) CH3CH2C(CH3)=CH2
2-methylbut-1-ene
The product obtained from the ozonide depends on the nature of the reagents used. Here we small use of Zn and acid to give aldehyde and/or ketones.
CH3CH2CH2CH=CH2
CH3CH2CH2CHO + HCHO
CH3CH2CH=CHCH3
CH3CH2CHO + CH3CHO
CH3CH(CH3)CH=CH2
CH3(CH3)CHCHO + HCHO
CH3C(CH3)=CHCH3
CH3(CH3)C=O + CH3CHO
CH3CH2C(CH3)=CH2
HCHO + CH3COCH2CH3