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 carbonyl 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 (NH3). A hydrogen is replaced by a carbon-nitrogen bond.

Amines are Bases R-NH2 + H2O  R-NH3+ + OH- Ammonia, and amines hydrolyze water occasionally: R-NH2 + H2O  R-NH3+ + OH- The 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.

Peptide Bonds

Amides and the Spice Trade Before refrigeration, food preservation was enhanced by using spices Colonization was driven by spice trade

Naming Amines and Amides The suffix –amine and –amide are added to the end of the hydrocarbon. The position of the amine functional group must be specified.

Uses of Amines Dyes: Yellow #6 Drugs - ephedrine (decongestant) - amphetamines (stimulants) - chlomipramine (antidepressant) - chloropromazine (tranquilizer)

Classify the following compounds according to their functional group, and name them.

Rank Compound Boiling Point (°C)   Propanone 56.2° Propyne -23.2° Propane -42.1° Propanoic acid 141.0° Propanal 48.0° Propene -47.4° 1-Propanol 97.0° Methyl Ethyl Ether 7.4° Methyl ethanoate 57.0° Propanamide 79.2° 1-Propanamine 105°

Draw these molecules Propanone 56.2° Propyne -23.2° Propane -42.1°   Propanone 56.2° Propyne -23.2° Propane -42.1° Propanoic acid 141.0°

  Propanal 48.0° Propene -47.4° 1-Propanol 97.0° Methyl Ethyl Ether 7.4°

  Methyl ethanoate 57.0° Propanamide 79.2° 1-Propanamine 105°

CH3CHF2 CH3CH2CH(NH2)CH3 CH3OH CH3CH2COOH CH2=CH2 CH3C=CCH2CH3   CH3CH2CH(NH2)CH3 CH3OH CH3CH2COOH CH2=CH2 CH3C=CCH2CH3 CH3CH2OCH2CH2CH2CH3 CH3CH2COOCH2CH2CH2CH3 CHOCH2CH2CH2CH3 CH3CH2COCH2CH2CH2CH3

CH3CH2CH2CH2CH2CH3 CH3CH(CH3)CH2CH2CH3 CH3CH2OOCCH2CH3 CH3CH2CH(OH)CH3   CH3CH(CH3)CH2CH2CH3 CH3CH2OOCCH2CH3 CH3CH2CH(OH)CH3 CH3CH2CHO CH3CH2CHCHCH2CH3 HCCCH2CH3 CH3CH2OCH2CH3 CH3CH2CONH2 HOOCCH2CH2CH3

Identify functional groups in the following molecules Phenylephrine (decongestant) Methyl ethanoate