Download Organic Functional Groups: Aldehydes, Ketones, Acids, Esters

Organic Functional Groups:
Aldehydes, Ketones, Acids, Esters, Amines, and Amides
Carbonyl Groups
• Carbon’s ability to share more than one
electron with an atom is often exploited by
greedy oxygen atoms.
• Oxygen will form double bonds with carbon
nearly as easily as carbon does with itself.
• These carbon-oxygen double bonds are called
carbonyl groups. There are two types of
carbonyl groups.
Aldehydes and Ketones
• Aldehydes are carbonyl groups that contain at
least one hydrogen atom. They have the
general formula RCHO.
• Ketones are carboxyl groups that are joined to
two other carbons. They have the general
formula RCOR.
Naming Aldehydes
• For aldehydes, compounds are named by
finding the longest hydrocarbon chain and
adding an –al suffix to the end of the parent
chain.
• Aldehydes don’t have to be numbered. Can
you think of a reason why?
• Aldehydes and ketones with the same number
of carbons are isomers of one another. You
will verify this for yourself later.
Naming Ketones
• For ketones, you find the longest hydrocarbon
chain and add a –one suffix to the end.
• The ketone, with two hydrocarbon groups
surrounding its carbon, is a secondary
carbonyl group.
• Ketone groups do need to be numbered.
Name These Compounds
Properties of Carbonyl Compounds
• Aldehydes and ketones are less polar than
similar sized alcohols.
• Their boiling points are thus lower than
alcohols.
• They are good solvents for both polar and
non-polar substances.
• The oxygen is fairly reactive, and many of
these compounds are toxic, carcinogenic.
Carboxylic Acids
• A carboxyl group is really a combination of
two other functional groups, a hydroxyl group
and a carbonyl group:
Carboxyl groups are also written as – COOH or, less commonly, CO2H.
Organic Acids
• The combination of these two polar groups
produces an extremely polar side group, the
organic acid.
• In an acid, the hydrogen atom can lose its
share of the electron pair completely to the
oxygen atom, and is cast off into the
surrounding water molecules:
R-COOH  R-COO - + H+
R-COOH + H2O R-COO - + H3O+
• The hydrogen becomes associated with a water
molecule, which becomes a hydronium ion
(H3O+) and the acid group becomes a negative
ion, RCOO-.
• The presence of the hydronium ion in water
makes the mixture an acidic solution.
• How often does this happen? Not very.
• Between one in a thousand and one in 100,000
organic acid molecules are dissociated at any
given time, depending on the acid.
Naming Organic Acids
• Take the parent chain name, and add the
suffix –oic plus the word acid.
• Since carboxylic acids are usually at the end of
molecules, they rarely appear with numbers.
Esters
• Esters are products of condensation reactions
of carboxylic acids and alcohols.
• In the presence of acid, a molecule of water is
removed:
CH3CH2CH2CH2OH + CH3COOH  CH3CH2CH2CH2OOCCH3 + H2O
alcohol
acid
ester
water
Naming Esters
• The alcohol
becomes a alkyl
branch
• The acid part is
changed from –oic
to –oate.
Properties of Organic Acids and Esters
• Organic acids are extremely common in
nature. They have the strongest
intermolecular forces and the highest boiling
points because of their partial ionization.
• Esters are far less polar, and are similar to
ethers and carbonyl groups.
• Esters are often pleasant smells, and are less
toxic than ethers, aldehydes and ketones.
Functional Groups of Nitrogen:
Amines and Amides
• Nitrogen is less electronegative than oxygen,
so its organic molecules are somewhat less
polar than some of the oxygen functional
groups.
Amines (R-NH2)
• An amine group is similar to ammonia. A
hydrogen is replaced by a carbon-nitrogen
bond.
Amines are Bases
• Ammonia, and amines hydrolyze water
occasionally:
R-NH2 + H2O  R-NH3+ + OHThe OH- product makes the solution basic (pH>7)
This makes amines extremely polar, nearly as
polar as acids.
Amides (R-CONH2)
• When amino acids are joined together in
ribosomes, the carboxyl group of one amino
acid is joined with the amino group of
another, producing water and an amide bond.
• Biologists refer to it as a peptide bond.
Naming Amines and Amides
• The suffix –amine and –amide are added to
the end of the hydrocarbon.
• The position of the functional group must be
specified.