Meet the (Most Important) Functional Groups

A functional group is what we call specific groupings of certain atoms within molecules that have their own characteristic properties.

Here are some of the most commonly encountered functional groups. Note that “R” is a placeholder for a generic carbon substituent.

A second group of slightly less commonly encountered functional groups are here. This is by no means an exhaustive list, but it’s at least a good start.

In the beginning of the course, being presented with a list of 20-25 functional groups to remember might seem like a lot. And it probably is!

The good news is that you’ve already learned a lot of functional group names without trying too hard.

Do these names sound familiar?

Propane. Tylenol. Ibuprophen. Testosterone. Dopamine.

Learning functional groups will be a matter of connecting those names to general structures.

Another good way to get to know functional groups is to think about the relative electronegativities of the elements in each group. That will help you understand their properties and help you think about how they behave in chemical reactions.

2. Alkanes, Alkenes, Alkynes, and Aromatic Rings

The hydrocarbon functional groups are very non-polar and tend to be extremely weak acids.

In hydrocarbons, the only types of intermolecular interactions are London dispersion forces and their boiling points tend to be quite low, relative to molecules containing more polar functional groups.

Alkanes are hydrocarbons containing no multiple bonds. Alkane substituents are called alkyl groups, which refers to alkanes lacking a C-H bond such as methyl, ethyl, or propyl.

• Common examples of alkanes are methane, ethane, propane, butane, and octane.
• The C-H bond is highly covalent and alkanes are very non-polar. They do not mix with water.
• Alkyl carbons are sp 3 hybridized and have tetrahedral geometry about the carbon.
• You can often think of alkyl groups as the “spectator” functional groups of organic chemistry, abbreviated as R-. With the exceptions of free-radical substitution and, of course, combustion, alkanes don’t undergo a huge number of different reactions. They tend to provide the backbone of most organic molecules.

Alkenes are hydrocarbons with one or more carbon-carbon double bonds.

• Common examples are ethene, propene, and butene.
• Alkene substituents are called alkenyl groups; vinyl is often used to refer to -CH=CH₂ .
• Alkenyl carbons are sp 2 hybridized, with a trigonal planar geometry.

Alkynes contain a carbon-carbon triple bond.

• Ethyne (acetylene) is the simplest alkyne; alkynes are sometimes called acetylenes.
• Alkyne substituents are called alkynyl groups.
• Terminal alkynes have a C-H. Internal alkynes have C-C bonds at each end.
• Alkynyl carbons are sp hybridized with a linear geometry.

Benzene rings are six-membered rings containing 3 double bonds. Benzene rings are common in nature due to a property called aromaticity (nothing to do with its smell) that make them unusually stable. Can also be drawn as a hexagon with a circle.

• Benzene, methylbenzene (toluene) is responsible for the smell of model airplane glue.
• Benzene substituents C₆H₅– are called phenyl groups.
• The carbons in benzene are sp 2 hybridized with trigonal planar geometry.

Draw examples of alkanes, alkenes, alkynes, and aromatic rings.