Alkane nomenclature

 

ALKANES:

Alkanes are a family of organic compounds that consist exclusively of carbon (C) and hydrogen (H) atoms bonded together through single covalent bonds.

 

They are often referred to as "saturated hydrocarbons" because they contain the maximum number of hydrogen atoms possible for a given number of carbon atoms, resulting in a saturated molecular structure.

General formula for alkanes:
                             CnH2n+2
where "n" represents the number of carbon atoms in the molecule.
Alkanes can be linear or branched in their molecular structure, depending on how the carbon atoms are arranged.

Properties:

• Alkanes are relatively inert and non-reactive compounds under normal conditions, as the single bonds between carbon atoms are strong and stable. 
• They are important as a source of energy, such as in natural gas and petroleum, and serve as the foundation for more complex hydrocarbons and organic compounds found in various fuels, chemicals, and materials.

IUPAC NAMING OF ALKANES RULE:

1. Identify the Longest Carbon Chain: Start by identifying the longest continuous chain of carbon atoms in the molecule. This chain is called the "parent chain" and forms the backbone of the alkane's name
2. Name the Parent Chain: Use the prefix associated with the number of carbon atoms in the parent chain:

• 1 Carbon: Meth-ane

• 2 Carbons: Eth-

• 3 Carbons: Prop-

• 4 Carbons: But-

• 5 Carbons: Pent-

• 6 Carbons: Hex-

• 7 Carbons: Hept-

• 8 Carbons: Oct-

• 9 Carbons: Non-

• 10 Carbons: Dec-

• 11 carbons: undecane

• 12 carbons: dodecane

• 13 carbons: tridecane

• 14 carbons: tetradec-

• 15 carbond pentadec-

• 16 carbons: hexadecane

• 17 carbons: heptadecane

• 18 carbons: octadecane

• 19 carbons: nonadecane

• 20 carbons: eicosame or icosane
• 3Number the Carbon Atoms: Assign a number to each carbon atom in the parent chain, starting with the end closest to a substituent (if any). The numbering should give the lowest possible numbers to substituents.
• 4Name Substituents: If there are any substituent groups (groups other than hydrogen) attached to the parent chain, name them using the appropriate prefixes and add them to the parent chain name.choose longest chain with more possible number of substituents.

• For example, a methyl group (CH3) is named as "methyl." Ethyl for ethane.
• 5Indicate the Position of Substituents: Use numbers to indicate the position of substituent groups on the parent chain. These numbers should correspond to the carbon atom to which the substituent is attached.

6. Combine the Names: Combine the names of the parent chain and substituents, listing them in alphabetical order. Use hyphens to separate numbers and commas to separate numbers from multiple substituents.
7. Complete the Name: If there is more than one substituent of the same type, use prefixes like "di-" (2), "tri-" (3), "tetra-" (4), etc., to indicate the number of identical substituents.
8. Check for Isomerism: In some cases, isomerism can occur in alkanes with branching. Ensure you have correctly identified and named isomeric structures if applicable.
9. Use Prefixes for Multiple Bonds or Rings: If there are multiple bonds (e.g., double or triple bonds) or rings in the molecule, use prefixes like "cyclo-" for rings and numerical prefixes for multiple bonds.\
10. Cyclic rings are preffered over chain as main ring and chain is considered as substituent.

Example practice for chain alkanes:

Substituent given priority and lowest number.

Numbering always begin with lowest priority number.

In the below example, we give both of the substituents lowest possible numbers as in cross example butyl has lowest 4 number but methyl has 7 number , in contrast with right picture tert-butyl has 5 number and methyl has 2 number.

If same number of carbons from either side of substituent, than numbering tosubstituents given according to alphabetical order as shown below.

1)      
9-ethyl-3,6-dimethyldodecane   

2)

3)        2,3-dimethylheptane 

4)     

      3-methylheptane
5)  

        4-tert-butyl-3-methylheptane
6)

 3-ethyl-2,2,4-trimethylhexane
7)     

        4-(butan-2-yl)-3,3-dimethyloctane
8)     

 3,9,9-trimethyldodecane
9)   

  8-ethyl-2-methyldecane
10)  

    2,2,3,3-tetramethylbutane
11)  

  4-tert-butyl-5-methyloctane
12)  

 4-tert-butyl-5-ethyloctane
13)   

14) 

2,4,5,7-tetramethyloctane

         
15) 

4-ethyl-2,5,7-trimethyloctane

16)   

5-ethyl-2,3,4,7-tetramethyloctane

17)   

2,3,4,7-tetramethyl-5-(propan-2-yl)octane

18)   

5-ethyl-2,7-dimethyl-4-(propan-2-yl)nonane

19)   

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4-ethyl-2,7-dimethyl-5-(propan-2-yl)octane

20) 

4-tert-butyl-3,6-dimethyloctane

21)   

3,6-dimethyl-4-(propan-2-yl)octane

22)   

2,3,4,5,6-pentamethylheptane

23)                                                                                                                  

 

4-ethyl-5-propyloctane

  24)                                                                                                                          

3,6-dichloro-4-ethyl-5-propyloctane

25)                                                                                                                   

4-ethyl-2-methyl-6-(propan-2-yl)nonane

Solve exercise 👀

Q : Draw structures Practice Problems

• 4-ethyl-2,2,6-trimethyl-3-(propan-2-yl)heptane

• 4-ethyl-2,2-dimethyl-3-(propan-2-yl)heptane

• 3,4-diethyl-2-methylheptane

• 4-ethyl-3-methylheptane

• 4-ethyl-3,6-dimethylnonane

• 3,6-diethyl-2,4,7-trimethylnonane

• 3-ethyl-2,6,7-trimethyl-4-(propan-2-yl)octane

• 3-ethyl-2,4,6,7-tetramethyldecane

• 3-ethyl-4,6,7-trimethylundecane

• 2,3,6-trimethyl-5-(propan-2-yl)octane

• 4-tert-butyl-2,3,6-trimethyloctane

• 2,2,5-trimethyl-3-(propan-2-yl)hexane

• 3-ethyl-2,4-dimethylpentane

• 3,4-diethyl-2-methylhexane