M7_Lecture

Module Overview

  • Title: Aldehydes and Ketones - MTCHEM1 Lecture

  • Instructor: Mr. Jan Clarence Salinas

  • Institution: Angeles University Foundation, College of Allied Medical Professions (CAMP)

Objectives

  • Explain the physical properties of aldehydes and ketones

  • Explain the chemical properties of aldehydes and ketones

  • Discuss the classical and IUPAC nomenclature of aldehydes and ketones

Outline

  • What are aldehydes and ketones?

  • How do we name aldehydes and ketones?

  • What are the physical properties of aldehydes and ketones?

  • What are the characteristic reactions of aldehydes and ketones?

  • What is acetal hydrolysis?

Properties of Carbonyl Group

  • Definition: A carbon atom double-bonded to an oxygen atom.

  • Structure: Trigonal planar with bond angles of 120°.

Selected Common Aldehydes and Ketones

Aldehydes

  • Formaldehyde: Simplest aldehyde produced by the oxidation of methanol; used in formalin for preserving biological specimens.

  • General formula: RCHO

Ketones

  • Acetone: A colorless, volatile liquid; simplest ketone used in industries, also found in nail polish removers.

  • General formula: RCOR

Nomenclature of Aldehydes

Rules for IUPAC Naming

  • Rule 1: Select the longest carbon chain including the carbonyl carbon.

  • Rule 2: Carbonyl must be carbon 1.

  • Rule 3: Change the suffix -e to -al for aldehydes.

  • Example: Hexanal from hexane

Common Aldehydes

  • Methanal (formaldehyde), Ethanal (acetaldehyde), Propanal (propioaldehyde), Butanal (butyraldehyde)

Nomenclature of Ketones

IUPAC Naming Rules

  • Rule 1: Select the longest chain containing the carbonyl carbon

  • Rule 2: Change -e of alkane to -one.

  • Example: Hexan-3-one from hexane.

Physical Properties of Aldehydes and Ketones

  • Polarity: Both are polar compounds.

  • Solubility:

    • Soluble in water if <6 carbons.

    • Soluble in organic solvents >6 carbons.

  • Boiling Point: Higher than hydrocarbons, lower than corresponding alcohols.

  • Melting Point: Generally increases with molecular mass.

Characteristic Reactions of Aldehydes and Ketones

  • Oxidation:

    • Aldehydes oxidize to carboxylic acids.

    • Ketones are resistant to oxidation.

Tests and Reactions

Tollens’ Test

  • Uses silver(I) oxide; only aldehydes yield a positive result (silver mirror).

Benedict's Test

  • Differentiates between aldehydes and ketones by forming a brick-red precipitate for aldehydes.

Reduction

  • Aldehydes and ketones can be reduced to form alcohols.

    • Aldehydes yield primary alcohols; ketones yield secondary alcohols.

Formation of Hemiacetals and Acetals

  • Hemiacetal: Formed when an aldehyde or ketone reacts with one alcohol molecule.

  • Acetal: Produced by reacting a hemiacetal with another alcohol molecule.

Acetal Hydrolysis

  • Converts acetals back to aldehydes or ketones with alcohols in the presence of acid.

References

  • Stoker, H. S. (2010). General, Organic, and Biological Chemistry, Fifth Edition. Brooks/Cole: Cengage Learning.

Conclusion

  • Questions can be directed to the discussion board or via direct message.