Definition of Hydrocarbons
Hydrocarbons are the simplest organic compounds. They are formed only by two types of atoms which are carbon and hydrogen. The question here is: “How many different compounds do you think two elements can form ?” There is thousands of hydrocarbons. The simplest hydrocarbon is methane which is the main component of natural gas, it is formed by only one carbon related to four hydrogen. The molecular formula of methane is CH4 .
In a hydrocarbon, carbon atoms can bond together by single, double, and triple bonds giving two main types of hydrocarbons: saturated and unsaturated.
Saturated hydrocarbons contain one single bond between carbon atoms and they are called Alkanes , but unsaturated hydrocarbons contain double or triple bonds between carbon atoms and they are called Alkenes (double bonds) and alkynes (triple bonds) .
Alkanes are the saturated hydrocarbons that have only single bonds between carbon atoms. Methane is the smallest one.
|Number of Carbon||Name||Molecular formula|
For alkanes, the general relation between the number of Carbons and the number of Hydrogen can be expressed as Cn H2n+2 n : Number of carbon
Example : if n= 11 2n + 2= 22+2 = 24
This alkane contains 11 atoms of carbon and 24 Hydrogen Molecular formula : C11H24
Straight chain alkanes contain carbon atoms that are bonded to each other in a single straight line. There is another form of alkanes which are branched chain alkanes, they contain a straight chain called “parent chain” and branches called “substituent group”.
Substituents are alkyl groups, the first four alkyl are mentioned in this table:
Naming Branched chain alkanes
A step by step strategy is used to name the branched chain alkanes :
Step 1: Count the number of carbon atoms in the longest continuous chain.
Step 2: Number each carbon in the parent chain, starting with the carbon closest to the substituent group. This gives all the substituent groups the lowest position numbers possible.
Step 3: Name each alkyl group substituent.
Step 4: If the same alkyl group appears more than once as a branch on the parent structure, use a prefix (di- , tri-, tetra- , and so on) before its name to indicate how many times it appears.
|Number of the same alkyl group||Prefix|
Step 5: When different alkyl groups are attached to the same parent chain, place their names in alphabetical order.
Step 6: Write the entire name, using hyphens to separate numbers from words and commas to separate numbers.
Many examples are shown in the pictures below
Chemical properties of alkane
Alkanes have low reactivity because they are nonpolar and have no charge, and because they have strong single bonds between carbon atoms.
Alkenes are unsaturated hydrocarbons that contain at least one double covalent bond between carbon atoms. The simplest alkene has two carbon atoms with a double bound between them and they are bounded to 4 hydrogen atoms to give the molecule ethene (C2H4).
|Number of Carbon||Name||Molecular formula||Structural formula|
|2||Ethene||C2 H4||CH2 = CH2|
|3||Propene||C3H6||CH2 = CH – CH3|
|4||1-Butene||C4H8||CH2 = CH – CH2 – CH3|
|4||2-Butene||C4H8||CH3 – CH = CH – CH3|
For alkenes, the relation between the number of Carbons and Hydrogen can be expressed as Cn H2n
n : Number of carbon
Example : if n=11 2n= 22
This alkene contains 11 atoms of carbon and 22 Hydrogen. The molecular formula : C11H22
Alkenes are named in much the same way as alkanes. But Alkenes end in –ene. And when four or more carbon atoms are present, the location of the double bond is specified by a number before the name of the parent chain.
When naming branched-chain alkenes, follow the same rules as for alkanes, with two exceptions: First the parent chain is always the chain that contains double bond, whether it is the longest or not and the second is that the first carbon should be the one closer to the double bond.
The picture below represent some examples
Alkynes are unsaturated hydrocarbons that contain at least one triple covalent bond between carbon atoms. The simplest alkene has two carbon atoms triple bounded to each other and bounded to 2 hydrogen atoms to give the molecule ethyne (C2 H2).
For alkynes, the relation between the number of Carbons and Hydrogen can be expressed as CnH2n-2
n : Number of carbon
Example : if n=11 2n – 2 = 22 – 2 = 20
This alkane contains 11 atoms of carbon and 20 Hydrogen. the molecular formula is: C11H20
Straight-chain and branched-chain alkynes are named in the same way as alkenes, except the ending is –yne.