Overview
This lecture covers the structures, properties, and preparation of four important organic functional groups: aldehydes, ketones, carboxylic acids, and esters, focusing on the carbonyl group and its reactivity.
The Carbonyl Group and Functional Families
- The carbonyl group (C=O) is a central feature in aldehydes, ketones, carboxylic acids, and esters.
- Carbonyl carbons are trigonal planar and exhibit sp² hybridization.
- The C=O bond is polar due to oxygen’s higher electronegativity.
Aldehydes and Ketones
- Aldehydes have the carbonyl group bonded to at least one hydrogen atom (general formula: CHO).
- Ketones have the carbonyl group bonded to two carbon atoms (general formula: C(O) or CO).
- Both use suffixes: "-al" for aldehydes, "-one" for ketones.
- Aldehydes are typically formed by oxidation of primary alcohols (OH group at chain end).
- Ketones are formed by oxidation of secondary alcohols (OH group on internal carbon).
Oxidation and Reduction in Organic Chemistry
- Oxidation is defined as replacing C–H bonds with C–O bonds.
- Reduction is replacing C–O bonds with C–H bonds.
- The oxidation number of carbon increases with more bonds to oxygen and decreases with more bonds to hydrogen.
Carboxylic Acids
- Carboxylic acids contain a carbonyl and a second oxygen bonded to a hydrogen (–COOH group).
- They are weak acids, only partially ionizing in water.
- Prepared by further oxidation of aldehydes or suitable alcohols.
Esters
- Esters contain a carbonyl with a second oxygen bonded to another carbon (–COOR group).
- They are formed by the reaction of a carboxylic acid with an alcohol.
- Esters have characteristic fruity odors and are present in many natural flavors and fragrances.
Properties and Uses
- Formaldehyde (HCHO) is a preservative and disinfectant.
- Acetone (CH₃COCH₃) is a widely used solvent.
- Acetic acid (CH₃COOH) is found in vinegar and industrially important.
- Esters are key components of fats, oils, and flavor compounds in fruits.
Key Terms & Definitions
- Carbonyl group — A functional group with a carbon-oxygen double bond (C=O).
- Aldehyde — Organic compound with a carbonyl group bonded to at least one hydrogen.
- Ketone — Organic compound with a carbonyl group bonded to two carbons.
- Carboxylic acid — Compound with a carbonyl group and a –OH attached to the same carbon.
- Ester — Compound with a carbonyl group and an –OR group attached to the same carbon.
Action Items / Next Steps
- Review oxidation numbers for organic molecules.
- Practice naming and drawing structures of aldehydes, ketones, carboxylic acids, and esters.
- Complete end-of-section exercises to reinforce understanding.