Overview
This lecture reviews key organic chemistry concepts and exam-style questions for Test 3, focusing on reactivity, nomenclature, functional groups, and reaction patterns.
Reactivity of Ketones vs. Aldehydes
- Aldehydes are more reactive than ketones due to less steric hindrance (hydrogen vs. alkyl group) and less electron donation to the carbonyl carbon.
- Ketones have two electron-donating alkyl groups, making them less electron-deficient and more stable.
- Reactivity is linked to ease of nucleophilic attack at the carbonyl carbon.
Oxidation and Reduction in Organic Chemistry
- Oxidation in organic chemistry means increased C–heteroatom bonding, fewer C–H bonds, or more double bonds.
- Reduction refers to the reverse: more C–H bonds and fewer C–heteroatom bonds.
Aromatic Substitution and Directing Effects
- Ortho/para directors (e.g., methyl group) guide new substituents to positions 2, 4.
- Meta directors (e.g., nitro group) guide new substituents to the 3 position.
- Recognize the impact of existing groups on substitution pattern in benzene rings.
Hydrogenation and Reductions
- Excess Hâ‚‚ reduces both C=C and C=O bonds; limited Hâ‚‚ reduces only the C=C bond.
- In oxidation, formation of a new multiple bond and/or new heteroatom attachment indicates oxidation.
Nomenclature and Stereochemistry
- Longest carbon chain determines base name; functional groups have priority in numbering.
- Assign priorities for stereochemistry (R/S) based on atomic number and substituent attachment.
- Alpha carbon in amino acids is bonded to both amino and carboxyl groups.
Boiling Point and Solubility Trends
- Alcohols (O–H) enable stronger hydrogen bonding than amines (N–H), leading to higher boiling points.
- Smaller non-polar carbon chains increase water solubility of alcohols.
Classification and Naming of Functional Groups
- A secondary amine has two alkyl groups on nitrogen; primary amine has one.
- Peptide bonds are amide bonds linking amino acids.
- Tripeptide = 3 amino acids; tetrapeptide = 4, oligopeptide (<40), polypeptide (>40).
- Aromatic compounds with special names: toluene (methylbenzene), aniline (aminobenzene), styrene (ethenylbenzene).
Key Terms & Definitions
- Steric Hindrance — Physical crowding around a reactive site, impeding reactions.
- Electron-Donating Group (EDG) — Substituent that donates electrons, stabilizing positive charges.
- Ortho/Para Director — Substituent guiding new groups to positions 2,4 on benzene.
- Meta Director — Substituent guiding new groups to position 3 on benzene.
- Peptide Bond — An amide bond between the carboxyl and amino groups of amino acids.
- Alpha Carbon — The carbon adjacent to the carboxyl group in amino acids.
Action Items / Next Steps
- Review and practice aromatic substitution directing effects and nomenclature rules.
- Study boiling point and solubility trends for alcohols and amines.
- Prepare for questions on functional group identification and stereochemistry.
- Watch the review video again before the exam.