Functional groups are specific groups of atoms within molecules that have very characteristic properties regardless of the other atoms present in a molecule. You’re probably familiar with several of them by now – alcohols, amines, carboxylic acids, ketones, and ethers are all common examples.
How many functional groups are there? Depending on how fine you slice your definitions, dozens and dozens. Wikipedia lists 197 pages for them. Yikes.
Thankfully, the 80/20 rule applies. In a typical sophomore organic chemistry course, there’s about 14 functional groups that are key, with another group of 8 that make appearances from time to time. [You'll meet others, too - this is just a selection of the most common]
Below you’ll find a presentation of the most common functional groups.
Things to think about as you look at the list:
1) in each, what are the most and least electronegative atoms present?
2) which of the atoms will be delta positive and which delta negative?
3) Which functional groups will be capable of hydrogen bonding?
4) Which functional groups will be capable of dipole-dipole interactions?
The more polar the molecule, the stronger the intermolecular interactions and the higher the boiling point. Which of these functional groups will tend to lead to the greatest increase in boiling points?
The more polar the molecule, the higher the water solubility. Which of these groups will tend to increase water solubility? Decrease water solubility?
Then there’s a group of about 8 functional groups that you’ll see a little but less often but they still have their place:
If you find that you’re having a hard time recalling the structures of the functional groups, I put together aquiz [flashcards on memorize.com] that might be useful.