The unsaturated open chain aliphatic Hydrocarbons Alkenes and Alkynes
Table of Contents
The unsaturated open chain aliphatic hydrocarbons
Unsaturated open chain hydrocarbons are a class of organic compounds that contain at least one carbon-carbon double bond (C=C) or triple bond (C≡C) in their molecular structure, and have a linear, unbranched chain of carbon atoms.
They are also referred to as alkenes (for compounds with a C=C bond) or alkynes (for compounds with a C≡C bond).
The double or triple bond in unsaturated hydrocarbons provides them with different chemical and physical properties compared to their saturated counterparts, which contain only single bonds between carbon atoms.
Unsaturated open chain hydrocarbons are commonly used in the production of various industrial chemicals, plastics, and fuels.
Some examples of unsaturated open chain hydrocarbons include ethene (C2H4), propene (C3H6), butene (C4H8), and pentene (C5H10) for alkenes, and ethyne (C2H2), propyne (C3H4), and butyne (C4H6) for alkynes.
Unsaturated open chain aliphatic hydrocarbons
The are classified into two groups:
1- Alkenes group:
They have a double bond or more in the carbon chain.
– C = C-
2- Alkynes group:
They have a triple bond in the carbon chain.
Alkenes (CnH2n)
1-They are Unsaturated open chain aliphatic hydrocarbons.
2-they are called Olefins (Alkenes) General formula (CnH2n)
3-Alkenes have a double bond, one of them is a strong (Sigma) bond and the other is weak (Pi) bond which is easily broken.
5-they are active GR?.
6-they are considered as alkanes derivatives by removing two hydrogen atoms from the corresponding alkane
7-They are a homogeneous series.
IUPAC Nomenclature of alkenes:
The nomenclature of alkenes is based on the International Union of Pure and Applied Chemistry (IUPAC) system, which is a set of rules for naming organic compounds. The basic rules for naming alkenes are as follows:
Find the longest continuous carbon chain that contains the double bond, and name it as the parent chain using the prefix corresponding to the number of carbon atoms (e.g. eth-, prop-, but-, pent-, etc.).
Number the carbon atoms in the parent chain starting from the end closest to the double bond. The double bond should be assigned the lowest possible numbers.
Name the substituents attached to the parent chain using the appropriate prefixes and alphabetical order. For example, a methyl group (CH3-) would be named as “methyl”, and an ethyl group (CH3CH2-) would be named as “ethyl”. If there are multiple substituents, the lowest possible numbers should be assigned to the substituents, and they should be listed in alphabetical order.
Indicate the location of the double bond by giving the number of the first carbon atom in the double bond. Use the infix “-ene” to indicate the presence of a double bond.
If there is a functional group present in the molecule, the double bond takes precedence over the functional group in determining the parent chain. The functional group should be named as a substituent, and the appropriate suffix should be used to indicate the functional group.
For example, the IUPAC name for CH3CH=CH2 would be:
prop-1-ene, since the parent chain is three carbons long, the double bond is located between the second and third carbon atoms, and there are no substituents present.
If there were a methyl group attached to the second carbon atom, the name would be:
2-methylprop-1-ene.
more examples :
CH2=CHCH2CH2CH3
This molecule contains five carbon atoms in the parent chain, with a double bond between the first and second carbon atoms.
The substituent on the fourth carbon atom is an ethyl group.
Therefore, the IUPAC name of this molecule is 4-ethylhex-1-ene.
CH3CH2CH=CHCH3
The parent chain in this molecule contains four carbon atoms, with a double bond between the third and fourth carbon atoms.
The substituent on the second carbon atom is an ethyl group.
Therefore, the IUPAC name of this molecule is 2-ethylbut-2-ene.
CH3CH=CHCH2OH
This molecule contains four carbon atoms in the parent chain, with a double bond between the second and third carbon atoms.
The functional group present in the molecule is an alcohol (-OH) group, which takes precedence over the double bond.
Therefore, the IUPAC name of this molecule is 3-hydroxybut-1-ene.
CH3CH2CH2CH=CHCH3
The parent chain in this molecule contains six carbon atoms, with a double bond between the fifth and sixth carbon atoms.
The substituent on the third carbon atom is a propyl group (CH3CH2CH2-).
Therefore, the IUPAC name of this molecule is 3-propylhex-1-ene.
Example1:
Write the IUPAC name of the following:
CH2 CH CH2 CH2 CH2 CH3
Example2:
CH2 CH CH (CH3) CH2 CH C lCH3
Example3:
draw the structural formula of the compound: 2-methyl-3-hexene
Example4:
Write the structural formula and the molecular formula of:
4-propyle -2-hepene
Example5:
3-bromo-2-methyl-1-hexene
Example6:
A hydrocarbon compound with molar mass 56 g/mol of this compound contains 48 g of contains: (c=12 ,H=1)
1)write the molecular formula of this compound
2) write the structural formula of two isomers of this compound
Answer:
1)-mass of hydrogen=56-48=8g
-no of moles =the mass of substance / the molar mass of the substance
Number of carbon atoms moles in this compound =48/12=4
Number of hydrogen atoms moles in this compound =8/1=8
The molecular formula of this compound is C4H8
2) 
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