Functional Groups

Common Functional groups  in organic chemistry.

Alkenes (C=C)

The compounds considered to this point have had the general formula C_nH_2n+2 and are termed the saturated hydrocarbons. The next groups of compounds considered are the alkenes. These compounds have the general formula of C_nH_2n. It can be seen that they differ from the alkanes in that they have 2 less hydrogen atoms in them. This means that they have a Carbon-Carbon double bond in the molecule. They are named the alkenes and are called unsaturated hydrocarbons.

NOTE: The exception is the cycloalkanes. These compounds will be discussed later.

The simplest alkene is ethene. The next member of the family is propene. The structure of these two compounds is shown below.

Alkynes (C≡C)

The general formula for the alkynes is C_nH_2n-2  and these compounds are also considered to be unsaturated. The smallest member of the family is ethyne a.k.a. acetylene. The structure of this compound as well as the next member of the family, propyne, is shown below.

Alcohols (ROH)

Alcohols are the next class of compounds. Most all alcohols are toxic to some extent. In representing the various types of functional groups chemists have adopted the formalism of using R- to represent any saturated alkyl group (those derived from the saturated alkane). This formalism and the smallest member of the family (methanol, CH₃OH) are shown below along with the structure of ethanol (CH₃CH₂OH) and 2-propanol (CH₃CHOHCH₃).  Notice the oxygen has two lone pairs and a hydrogen on it.  The chemistry of alcohols is driven by this acidic proton and the lone pairs.  They can act like acids or bases.

Amines (RNH₂)

The amines are organic compounds that contain nitrogen bonded to a carbon chain(s). The simplest member of the family is methyl amine. This gaseous compound is toxic and highly flammable. Ethyl amine is the next member of the family.  Because of the lone pair electrons on the N atom, amines are very basic.

Aldehydes (RCOH)

The smallest aldehyde is methanal (formaldehyde). It is a highly toxic gas. It also is a carcinogen and a teratogen. The next member of the family is ethanal (acetaldehyde).

The C=O double bond in aldehyde's is referred to as a carbonyl group.

Ketones (RCOR)

Ketones also have a carbonyl group, however, in ketones there are carbon containing groups on each side of the carbonyl.  The smallest possible ketone is propanone (acetone).

Carboxylic Acids (RCO₂H)

The carboxylic acids also contain a carbonyl group but an -OH (hydroxyl) group is attached to the carbonyl.  This is collectively referred to as a carboxyl (or carboxy group), -COOH. The simplest member of this family is methanoic acid (formic acid). Ethanoic acid is the next member of the family. It is also known as acetic acid . A 3% solution of ethanoic acid in water is vinegar.

Esters (RCO₂R)

The esters also contain a carbonyl group but an -OR is attached rather than an -OH group as in the carboxylic acids. The simplest member of the family is the methyl derivative of methanoic acid. This is given the name of methyl methanoate or methyl formate. The ester derivatives of ethanoic acid also have a common name, that of acetates. Ethyl acetate (ethyl ethanoate) is a common organic solvent that is found in finger nail polish remover.

Amides (RCONH₂)

Amides have an amine attached to a carbonyl carbon.

Anhydrides - (RCO)₂O

Anhydrides are not found in nature and are typically only synthesized in the lab.  The most prominent one is ethanoic anhydride (acetic anhydride).

Carboxylic Acid Halides (RCOX)

These compounds are usually considered a safety risk. The low molecular weight members of this family of compounds react vigorously with water to produce highly irritating products (Acids). The compounds have a halide (usually Cl or Br) attached to a carbonyl functional group.  Acid halides are not found in nature and are typically only synthesized in the lab.

Aromatics

This group encompasses a wide variety of compounds that contain a benzene or benzenoid (i.e. benzene like) component as part of their structure. The structure of benzene is shown below.