Recognizing Functional Groups
A Logical Organization
Chemical Structures of Functional Groups Listed Logically
Name of
Functional Groups
Generic
Form
Alkane or
Alkyl
Other Forms
Alkene
These functional groups (to the left) are all related in the sense that they
usually only consist of carbons and hydrogens. The difference is in the
number of bonds between the carbons.
Alkyne
Need a way to remember? The number of bonds goes in alphabetical order.
Notice: alkane (1 bond), alkene (2 bonds), alkyne (3 bonds).
Aryl or Aromatic
Ar
Notice that alkyl halides (below) are alkanes (above) with a halogen (Group 7 on Periodic Table) attached.
Alkyl Halide
primary
1º
secondary
2º
tertiary
3º
Notice that the only difference between alcohols (below) and ethers (below) is that in an alcohol an oxygen
is attached to one carbon and one hydrogen, and in an ether an oxygen is attached to two carbons.
Alcohol
primary
1º
Ether
secondary
2º
tertiary
3º
Carbonyl
Acyl
Notice that a carbonyl/acyl is present in the next six functional groups!
However, depending on what is attached to the these changes the name of
the functional group! Notice the difference between a carbonyl and and
acyl is that in the acyl we are including the attached carbon chain.
Aldehydes have a carbon and a hydrogen attached to the carbonyl, or they
have a hydrogen attached to the acyl. Notice that the oxygen must be on a
terminal carbon.
Aldehyde
Ketone
Need a way to remember? The name aldehyde comes from combining the
words "dehydrogenated alcohol". So "al" from "alcohol" plus "dehyde" from
"dehydrogenated" equals aldehyde.
(Dehydrogenated means removing the hydrogen.)
Ketones have two carbons attached to the carbonyl, or they have a carbon
attached to the acyl. Notice that the oxygen cannot be on a terminal
carbon.
Now we come to the Carboxylic Acid group and all of its derivatives: Acyl/Acid Halides, Amides, and Esters.
These groups also contain the carbonyl group, but here the acyl group is more often pointed out.
Carboxyl or
Carboxylic or
Carboxylic Acid
Acyl Halide or Acid
Halide
Carboxylic Acids have a carbon and an alcohol attached to the carbonyl, or
they have an alcohol attached to the acyl. Carboxylic acids can only be on
terminal carbons to maintain proper valence.
Why two names? Acyl Halide comes from the fact that there is a halide
attached to an acyl. Acid Halide comes from the fact that we have
replaced the alcohol from a carboxyl group with a halide. You can also
think of it as a carbon and a halide attached to a carbonyl!
Amides have a carbon and a nitrogen attached to the carbonyl, or they
have a nitrogen attached to the acyl.
Amide
Need a way to remember amides versus amines? Well, an amide is a
carboxylic acid derivative. Both "amide" and "acid" have a "d" in them,
"amine" does not.
An Ester has a carbon on one side of the carbonyl and an oxygen attached
to another carbon on the other side, or an oxygen is attached to both an
acyl and to a carbon.
Ester
Need a way to remember? An ester is usually formed by reacting a
carboxylic acid with an alcohol. So, the –OH on the carboxylic acid is
replaced by the –OR from the alcohol.
Amine
primary
1º
secondary
2º
tertiary
3º
Grignard or
alkylmagnesium
halide
Nitrile
Nitro
Thiol
Notice how Alkyl Halides, Alcohols, Amines can be primary, secondary, or tertiary. How do you tell? Well
for Alkyl Halides and Alcohols, look at the carbon that the special group (–X, –OH) is attached to. How
many carbons are attached to it? In a primary, only one is attached. In a secondary, two are attached.
Finally in a tertiary, three carbons are attached. For Amines, look at how many carbons are attached to the
nitrogen. In a primary, one carbon is attached and so on. What if there are no carbons attached? Then, it is
an ammonia and not an amine at all!