Functional Groups

We can group millions of different molecules into families of similar functionality.


  • All carbon groups regardless of size can be symbolized using an –R group.
  • When an alkane is attached to a greater carbon chain, it is given a –yl suffix
    • An alkane turns into an alkyl group.  
  • Carbons are given a “degree” based on how many other carbons they are attached to.
    • Degrees are expressed as primary, secondary, tertiary and quaternary (1o, 2o, 3o, 4o)
    • Hydrogens possess the SAME degree as the carbon they are attached to 

Example: Determine the degree of the indicated carbons and hydrogens. 


Alkyl Halides

  • Condensed Structure = -RX
  • The degree of the alkyl halide is determined the same exact way as hydrogen. 

Example: Use your knowledge of hydrogen degrees to assign degrees to the following alkyl halides. 


Functional Groups without Carbonyls

Carbonyls are C=O bonds within a molecule. First we’ll learn about common functional groups that don’t contain these.  

  • Alcohol Condensed Structure = -ROH
  • Amine Condensed Structure = -NH3, RNH2, R2NH, R3N
  • Ether Condensed Structure = ROR

These three functional groups completely change when they have a carbonyl next to them!

Functional Groups with Carbonyls

  • Carboxylic Acid Condensed Structure = -COOH
  • Amide Condensed Structure = -CONH2
  • Ester Condensed Structure = -COOR

As you see, these functional groups are similar to the other ones, but have different names due to the adjacent carbonyl. 

Adding Carbonyls to Hydrocarbons

Concept: How to write the condensed structures for aldehydes and ketones. 

  • Ketone Condensed Structure = -COR
  • AldehydeCondensed Structure = -CHO

These condensed structures aren’t very obvious. So just apply them to memory!

Other Carbonyl Compounds

Since sulfur is directly under oxygen in the periodic table, it makes analogous structures. These have different names depending on whether the sulfur is terminal (like alcohol) or internal (like ether). 

  • Thiol Condensed Structure = -RSH
  • Sulfide Condensed Structure = RSR

Problem: PRACTICE: The following molecule contains several functional groups. Of the choices given, select the most appropriate answer (not all functional groups may be listed). 


Problem: PRACTICE: Identifying functional groups. Select the most appropriate answer. 


Problem: PRACTICE: Identifying functional groups. Select the most appropriate answer.