II. Family: Alkanes

A. Definition: Organic hydrocarbon molecules in which all of the carbon atoms in the parent chain ( the longest continuous chain) are held together by single covalent bonds.

B. Rules for naming alkanes(prefix/substituted group parent sufix)

1. The longest chain of carbon (C) atoms is the parent.

# of C Atoms
Name
Molecular Formula
1
Methane
CH4
2
Ethane
C2H6
3
Propane
C3H8
4
Butane
C4H10
5
Pentane
C5H12
6
Hexane
C6H14
7
Heptane
C7H16
8
Octane
C8H18
9
Nonane
C9H20
10
Decane
C10H22

 

Note:

If two possible chains have the same number of C atoms, the parent is the one with the larger number of branch points.

 

2. Number the C atoms in the longest chain starting from the end of the parent chain nearer the first branch point.

      CH2-CH3              
     
|
              
CH3-
 CH- CH2- CH- CH2- CH3          
1
| 2
 3 4 5 6          
CH3                  

Note:

If the first branch occurs at an equal distance from each end of the parent chain, number the C atoms in the longest chain (parent) from the end that is nearer the second branch.

        CH2-CH3 CH3          
        | |          
CH3- CH- CH2- CH2- CH- CH2- CH2- CH3      
8 | 7 6 5 4 3 2 1      
  CH3                  

 

3. Each branch or substituent has a number that indicates its location on the parent chain. When two substituents are located on the same C atom, each must be assigned the same number.

          CH2-CH3 CH3      
          |          
CH3- CH2- CH2- CH- CH2- CH- CH2- CH- CH3    
9 8 7 | 6 5 | 4 3 2 1    
      CH2CH2CH3 CH3          

It is called: 4-ethyl-4-methyl-6-propyl-nonane

 

4. The number for the position of each alkyl group is placed immediately before the name of the group and is joined to the alkyl name by a hyphen. Alkyl groups and halogens are listed in alphabetical order.

        CH2-CH3            
        |            
CH3- CH- CH2- CH2- CH- CH2- CH3        
1 | 2 3 4 5 6 7        
  Cl                  

 

It is called: 2-chloro-5-ethylheptane .

Blue color = Prefix or substituted group

Red color = Parent root

Purple color = Suffix /class name      

5. Two or more groups of the same type are indicated by the prefixes di-, tri- and so forth. The numbers that indicate the locations of the branches are separated by commas.

 

  CH3                    
  |                    
CH3- CH- CH2- CH- CH2- CH3            
1 2 3 | 4 5 6            
      CH3                

 

It is called: 2,4-dimethylhexane

Blue color = Prefix or substituted group

Red color = Parent

Purple color = Suffix /class name

 

6. The prefixes di-, tri-,tetra- and so forth do not alter the alphabetical ordering of the alkyl groups.

CH2-CH3      
|      
CH3- CH2- CH- CH2- C- CH2- CH2- CH3      
1 2 | 3 4 | 5 6 7 8      
CH3 CH3      

 

It is called: 5-ethyl-3,5-dimethyloctane.

Blue colors = Prefix or substituted group

Red color = Parent

Purple color = Suffix/class/family

 

C. Rules for naming cycloalkanes.

1. Cycloalkane rings are numbered clockwise or counterclockwise to give the lowest number to the two or more substituted groups.

2. If there is only one substituted group on the cycloalkane, it will always be on the first carbon in the ring irregardless of positioning.

E.G.

 
 
 
     
           
           
                     
Cyclopropane   Cyclobutane   Cyclopentane   Cyclohexane      
                     
                     
                     

 

E.G.

    
 
     
           
           
                   
1-methylcyclohexane     1-chloro-3-methylcyclohexane        
                   
                   
                   

 

E.G.

    
 
     
           
           
                   
1,3-dimethylcyclohexane     1,2-dichloro-5-methylcyclohexane