In-Depth Notes on Organic Compounds and Isomerism

Nomenclature of Organic Compounds

  • Dr. M. Abd-Elhakeem, MISR University for Science and Technology
  • Understanding the naming conventions is crucial for grasping organic chemistry concepts.

Common Names of Organic Compounds

  • Familiarity with common names helps in recognizing and recalling chemical compounds.

Examples of Common Names:

  • Toluene: C7H8
  • Aniline: C6H7N
  • Phenol: C6H6O
  • Benzoic Acid: C7H6O_2
  • Xylene: C8H{10}
  • Anisole: C8H10O
  • Acetophenone: C9H{10}O
  • Naphthalene: C{10}H{8}

Drawing Structures from Names

  1. Start by drawing the parent chain based on the end of the compound name.
  2. Add functional groups in their correct positions.
  3. Incorporate any substitutions as necessary.

Examples of Structural Drawing

Compounds to Draw:

  • 3-Nitrotoluene: CH3 + NO2
  • 1,2-Dibromocyclopentane: C5H{8}, Br
  • 5-Hydroxyhexanoic acid: C6H{12}O_3
  • 2-Chloro-3-methyl-1-hexene: C6H{11}Cl
  • 2,3,4-Trimethylpentane: C8H{18}
  • 4-Chloro-2-butanone: C4H7ClO
  • Ethanal (Acetaldehyde): C2H4O

Isomerism in Organic Compounds

Definitions:

  • Isomers: Compounds with the same molecular formula but different structural arrangements.

Types of Isomerism:

  • Structural Isomerism: Variations in connectivity of atoms.
  • Geometric Isomerism: Different arrangements around a carbon-carbon double bond.

Examples:

  • Butane vs. Isobutane: Both have the formula C4H{10} but differ in structure.
  • Geometric isomers can have significant differences in physical and chemical properties.

Stereoisomerism and Chirality

  • Stereoisomerism: Molecules that have the same formula but differ in the spatial arrangement of atoms.
  • Chirality: Molecules that are non-superimposable on their mirror images (like left and right hands).

Biological Importance:

  • Natural vs. Unnatural products: (R)-(-)-epinephrine is active; (S)-(+)-epinephrine does not fit enzyme’s active site and thus has no activity.

Drug Optics and Implications

  • Optically active drugs may have one enantiomer beneficial and another harmful: e.g.
  • Thalidomide: Provided relief for morning sickness but caused severe birth defects due to enzymatic conversion in the body.

Types of Isomers

  • Constitutional Isomers: Differ in connectivity.
  • Diastereomers: Stereoisomers that are not mirror images; also include cis-trans isomers.
  • Enantiomers: Mirror images of one another.

Optical Activity

  • Polarimetry: Measurement of the rotation of polarized light.
  • Dextrorotatory: Clockwise rotation (+).
  • Levorotatory: Counterclockwise rotation (-).

Cahn-Ingold-Prelog (CIP) Priority Rules

  • Assign priority based on the atomic numbers of the atoms attached to a chiral carbon.

Assigning (R) or (S)

  1. Arrange the lowest priority group at the back.
  2. Determine the direction of counting from highest to lowest priority:
    • Clockwise = (R)
    • Counterclockwise = (S)

Fischer Projection

  • When lowest priority is oriented toward the viewer, assignments may seem reversed compared to usual methods.

Properties of Isomers

  • Physical Properties: Diastereomers differ in boiling/melting points; can be separated easily.
  • Enantiomers: Similar physical properties but differ in reactivity with chiral entities and the direction of light rotation.

(R) and (S) Nomenclature

  • Necessary to distinguish between different enantiomers as one is often biologically active.
  • Configuration is denoted by (R) or (S) based on priority assignment around the chiral center.

Summary

  • Mastery of organic nomenclature and isomerism is essential for a strong foundation in chemistry, particularly for drug design and understanding molecular interactions.