Functional Groups in Organic Synthesis & Analysis

Instructor: Sarah Pierce

Sarah has a doctorate in chemistry, and 12 years of experience teaching high school chemistry & biology, as well as college level chemistry.

This lesson is an introduction to functional groups in organic synthesis. Examples of functional groups in everyday life are given. A method for identifying functional groups is also discussed and applied to organic synthesis.

Functional Groups

Imagine a Christmas tree with blinking lights. Just like the lights on the tree 'do something' - they blink - functional groups also 'do something' - react - in organic molecules. Functional groups in organic chemistry are groups of molecules that react on a hydrocarbon chain.

The hydrocarbon chain is like the Christmas tree, while the functional group is like the lights. To figure out what exactly they do, it's important to be able to identify them.

Identifying Functional Groups

To find functional groups, look for molecules that are not just carbon and hydrogen atoms connected by a single bond. We can divide these into two broad categories:

  1. functional groups connected to a carbonyl group
  2. functional groups not connected to a carbonyl group

Functional Groups With Carbonyl Groups

When identifying functional groups, look for the carbonyl first. A carbonyl group has an oxygen with double bonds connecting it to a carbon. Then, look at the molecules connected to the carbonyl either on the left or the right of the molecule.

When identifying functional groups, look for a carbonyl (carbon double bond to an oxygen).

  • Ketone molecules contain just a carbonyl group with hydrocarbon molecules on either side.
  • Aldehyde molecules have a carbonyl group that at the end of a molecule.
  • Carboxylic acid molecules have an -OH next to a carbonyl group. This functional group is found at either the beginning or end of a molecule.

A ketone, aldehyde, and carboxylic acid. The red boxes highlight the functional groups

  • Ester molecules have just an oxygen atom next to a carbonyl group. This functional group is always found in the middle of the molecule.
  • Amide molecules have a nitrogen atom next to a carbonyl group. These bonds hold the amino acids together and are an excellent example of an amide.

An ester and amide molecule (note the oxygen and nitrogen, respectively

Functional Groups Not Connected to Carbonyl Groups

Let's move on to functional groups that are not connected to carbonyl groups. Note that just because the functional groups aren't directly connected to a carbonyl group, this does NOT mean that the molecule can't have a carbonyl group in it.

  • Alkene molecules have a carbon double bond
  • Alkyne molecules have a carbon triple bond
  • Alcohol molecules have an oxygen and a hydrogen atom.
  • Thiol molecules contain a sulfur atoms.
  • Ether molecules have an oxygen atom in the middle of the hydrocarbon molecule.
  • Amine molecules have a nitrogen atom.


Functional Groups in Organic Synthesis

Most of the time in organic chemistry, you will have one reactant with a functional group, a reagent will be added, and then your product will have a new functional group. Reagent is just another word for small molecule that participates in a chemical reaction. This can be molecules like water, acids, or bases.

For example, an alkene functional group reacts with the reagent water to form an alcohol.

An alkene functional group reacts with water to form a new functional group: an alcohol

There are many chemical reactions like this in organic chemistry: one functional group is turned into another functional group.

There are a few reactions in organic chemistry where two functional groups react together to form another functional groups. For these reactions, if you can identify the functional groups in the reactant, you can predict the functional group in the product. Let's look at three reactions where this occurs.

Reaction 1: If an alcohol and a carboxylic acid functional group react in the presence of an acid catalyst, they form an ester functional group.

Ethanoic acid and ethanol react to form ethyl ethanoate, the ester responsible for the sweet smell in nail polish remover

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