Lecture 10

Lecture Overview
  • Course: CHEM 2321-2324
  • Instructor: Dr. Robert Pankow
  • Content Usage: Only for students enrolled in the course. Not for copying, posting, selling, or editing.
Today's Lecture
  • Continuing with Nomenclature
  • Discussing notable functional groups:
    • Carbonyl Compounds and relative priority
    • Cycloalkanes
    • Alkenes and Alkynes
Nomenclature Priorities
  • IUPAC Priority Table (relevant for Midterm Exam II)
    • 1. Carboxylic Acid
      • Prefix: Carboxy-
      • Suffix: -carboxylic acid or –oic acid
    • 2. Ester
      • Prefix: Alkoxycarbonyl-
      • Suffix: -oate
    • 3. Amide
      • Prefix: Carbamoyl-
      • Suffix: -carboxamide or –amide
    • 4. Nitrile
      • Prefix: Cyano-
      • Suffix: -nitrile
    • 5. Aldehyde
      • Prefix: Formyl-
      • Suffix: -al or –carbaldehyde
    • 6. Ketone
      • Prefix: Oxo-
      • Suffix: -one
    • 7. Alcohol
      • Prefix: Hydroxy-
      • Suffix: -ol
    • 8. Alkene/Alkyne
      • Alkene: -en-; Alkyne: -yn-
      • Alkene Suffix: -ene; Alkyne Suffix: -yne
Naming Cyclic Structures
  • Prefix "cyclo" added to name to indicate cyclic nature
  • Defines number of carbons in the ring.
Naming Substituents on Rings
  • Example: (1-methylethyl)cyclohexane
  • Numbering around the ring must give the lowest possible numbers.
    • Notation 3-ethyl-1-methylcyclohexane is incorrect due to priority rules.
Numbering Guidelines for Rings
  • General Rules:
    • Number substituents to achieve the lowest possible configuration.
    • Alphabetical order influences numbering where all else is equal.
  • Example: Alkyl and halo groups have equal precedence, lowest numbering applies.
    • Avoid 5-chloro-1-ethyl-2-methylcyclohexane or 3-chloro-1-ethyl-5-methylcyclohexane.
Precedence Rules
  • Hydroxyl (–OH) has higher priority:
    • E.g., 1-phenyl-2-furanol should be named with lowest number for –OH.
Smallest Carbon Component Rule
  • The smallest carbon component becomes the substituent.
    • Example: 1-cyclopentylhexane is preferable to hexylcyclopentane.
Fused and Bridged Rings
  • Fused Rings: Two or more rings sharing a bond between nonadjacent carbon centers.
    • Terminology: Bicyclo, Tricyclo, Tetracyclo based on the number of fused rings.
  • Bridged Rings:
    1. Nonadjacent atoms common to two rings
    2. Bonded through one or more chains (bridges).
Important Compounds with Fused and Bridged Rings
  • Taxol:
    • Contains fused and bridged rings exemplified in diagrams of its structure.
Tetracyclic Compounds and Steroid Structure
  • General Steroid Skeleton represented as rings A, B, C, D.
  • Activity of steroids often linked to substituents on these rings.
Common Steroids
  1. Cholesterol
  2. Estradiol
  3. Ecdysterone (insect steroid)
  4. β-Sitosterol (plant steroid)
Polycyclic Nomenclature Guidelines
  1. Start at a bridgehead carbon that is part of the longest bridge.
  2. Continue numbering to the next bridgehead through the longest connections.
  3. Number the shortest bridge last.
  • Example: Bicyclo nomenclature that counts total carbons and defines bridges.
Examples of Named Structures
  1. Bicyclo[2.2.1]heptane with specific bridge scoring based on lengths.
  2. Example of 7-Methylbicyclo[4.3.0]nonane and 1-Isopropylbicyclo[2.2.2]octane.
Naming Alkenes and Cycloalkenes
  • Number substituents based on priority, achieving the lowest configuration.
  • In the presence of both alcohols and alkenes, alcohols take priority for suffix.
  • Use lowest numerical values for double bonds in assigned names.
Alkenes: Stereochemistry
  • Cis/Trans Stereoisomers relevant in nomenclature.
Understanding Alkynes
  • Rules similar to alkenes apply when naming, considering alphabetical order when both are present.
Student Expectations for First Semester
  • Knowledge areas required:
    • Straight chain alkanes, alkenes, alkynes with up to 12 carbons.
    • Monocyclic ring systems with substituents.
    • Polycyclic structures with bracket bridge notation (e.g., [a.b.c…]).
    • Naming and identifying Cis/trans configurations.
Practice Questions from Sections 4.3 - 4.5
  • Interpretation of complex structures and their IUPAC names (e.g., 2-bromo-6-isobutyl…).
  • Focus on identifying correct structures based on naming conventions introduced.
Closing Note
  • Lecture concluded with emphasis on understanding organic nomenclature and structure recognition.