Interchapter B Notes: Naming Alkenes, Alkynes, and Benzene Derivatives (Page-by-Page)

Page 1

• Topic: Interchapter B of Organic Chemistry (3rd edition, Joel Karty) focused on Naming Alkenes, Alkynes, and Benzene Derivatives.
• Scope: Principles and mechanisms for naming compounds containing C=C, C≡C, and benzene derivatives; emphasis on IUPAC rules and practical naming strategies.

Page 2

• B.1 Alkenes, Alkynes, Cycloalkenes, and Cycloalkynes: Molecules with one C=C or C≡C bond.
• Priority: The C=C and C≡C functional groups have higher priority than any substituents in Interchapter A.
• Root determination:
  1. Identify the analogous alkane or cycloalkane.
  2. Replace the alkane suffix: remove the “-ane” and add either:
  • “-ene” if the molecule contains a C=C bond.
  • “-yne” if the molecule contains a C≡C bond.

Page 3

• Numbering system for simple alkenes and alkynes:
  • For a chain: assign C-1 to the end from which the C=C or C≡C is encountered earliest.
  • For a ring: assign the two carbons of the C=C or C≡C bond as C-1 and C-2.

Page 4

• Constructing the IUPAC Name:
  1. Write the root name:
  • For an acyclic alkene or alkyne, identify the lower of the two locator numbers for the C=C or C≡C atoms and insert it before the ene or yne suffix. Hyphens separate numbers from letters.
  • For a cycloalkene or cycloalkyne, that locator number is typically not included because it is understood to be 1.
  1. Add prefixes.

Page 5

• SOLVED PROBLEM: Write the IUPAC name for the molecule shown here.
• The illustration shows a structure with two chlorine substituents (represented as CI) on the molecule. The exact IUPAC name is not provided in this page image, but the prompt indicates a named exercise to practice root selection, numbering, and substituent placement.

Page 6

• SOLVED PROBLEM: Think, Solve. Questions posed:
  • What is the longest carbon chain that entirely contains the C=C bond?
  • What is the corresponding root name?
  • On which end of the chain should numbering begin to allow the C=C group to be encountered the earliest?
  • Which locator number of the C=C atoms should be included in the IUPAC name?
• This page frames the method for determining the correct root, numbering direction, and which locants to include when a double bond is present.

Page 7

• SOLVED PROBLEM: Solve. Summary of given solution:
  • The longest carbon chain that entirely contains the C=C bond is six carbon atoms, so the root is hexene.
  • Numbering begins from the end that encounters the C=C group the earliest; the solution states the lower of the two locants is 2.
  • The IUPAC name is: $4,4$-dichloro-3-(1-methylethyl)hex-$2$-ene.
  • The question also asks which locator number of the C=C atoms should be included in the IUPAC name; the answer is the lower-numbered locant (2).

Page 8

• B.2 Molecules with Multiple C=C or C≡C Bonds – Naming a Molecule with More Than One C=C or C≡C Bond:
  1. Establish the root.
  2. Establish the numbering system for the chain or ring:
     a. The first C=C or C≡C group should be encountered the earliest.
     b. If there is a tie, the next C=C or C≡C group should be encountered the earliest.
  3. Locate each C=C or C≡C bond. For each pair of C=C or C≡C atoms, write the lower of the two locator numbers.
  4. Modify the suffix: Immediately before the ene or yne suffix, add the letter “a” followed by the above set of locator numbers, and then add a multiplier prefix (di, tri, etc.) to specify how many double or triple bonds are present.

Page 9

• SOLVED PROBLEM: Write the IUPAC name for the molecule. The page text shows the molecule label as “NO,” which is unclear from the transcription but indicates a problem involving multiple bonds or substituents.

Page 10

• SOLVED PROBLEM: Think, Solve. Questions:
  • What is the longest carbon chain that entirely contains all the C=C groups?
  • On which end of the chain numbering should begin so that the first C=C group is encountered the earliest?
  • How do you determine the set of locator numbers for the C=C groups?
  • When do you add the letter “a” before the suffix?
• These prompts guide the process for multi-bond systems and the appropriate use of the “a” infix before the suffix.

Page 11

• SOLVED PROBLEM: Think, Solve. There are three C=C groups and the longest chain containing all of them has seven carbon atoms.
  • What is the longest chain that contains all C=C groups?
  • Where should numbering begin to encounter the first C=C group the earliest?
  • How to determine the set of locator numbers for the C=C groups?
  • Because of multiple C=C groups, the letter “a” is added before the suffix, so this is a heptatriene.
  • Complete IUPAC name: $2$-ethyl-$6$-nitro-$3$-propylhepta-$1,3,5$-triene.
  • When do you add the letter “a” before the suffix? In cases with multiple C=C groups that require an expanded suffix (e.g., hexa-, hepta- trienes, etc.).

Page 12

• Naming Enynes: Molecules Having both C=C and C≡C Groups
  1. Establish the root. Use the suffix enyne.
  2. Establish the numbering system:
  • The C=C and C≡C groups are given equal priority unless there is a tie between two numbering systems.
  • If there is a tie, the tie is broken by giving priority to the C=C group.
  1. Add the locator numbers. Add the locator numbers for the C=C groups immediately before en and add those for the C≡C groups immediately before yne.
  2. Account for multiple C=C and C≡C groups. Add the letter “a” immediately before the corresponding locator numbers, and add the proper multiplier prefix (di, tri, etc.) immediately after.

Page 13

• B.3 Benzene and Benzene Derivatives:
  • Benzene (C6H6) Lewis structure features three C=C double bonds that alternate with three C–C single bonds in a six-membered ring.
  • Benzene is an aromatic compound.

Page 14

• Naming Benzene and Benzene Derivatives:
  1. Establish the root as benzene. Substituents attached to the ring are treated as substituents.
  2. Establish the numbering system of the ring. Give the lowest locator number to each successive substituent.
  3. Add prefixes and locator numbers. Account for the number, type, and location of each substituent.

Page 15

• SOLVED PROBLEM: Provide the IUPAC name for the molecule shown here.
• The figure shows a nitro group (NO2) and a chlorine substituent (CI) on the ring, indicating a nitro- and chloro-substituted benzene. The exact positional name is not stated in the transcription.

Page 16

• SOLVED PROBLEM: Think, Solve. Questions:
  • Is there a six-membered ring of alternating C–C and C=C bonds? What root is assigned in such cases?
  • Where should C-1 be assigned to allow each successive substituent to be encountered the earliest?
  • Should numbering proceed clockwise or counterclockwise?
  • How should you add prefixes to complete the name?
• This prompts consideration of rings with alternating single and double bonds and how to assign the root and numbering to minimize locants for substituents.

Page 17

• SOLVED PROBLEM: Solve. The six-membered ring of alternating C=C and C≡C bonds requires the root benzene.
• There is a six-membered ring of alternating C–C and C=C bonds; the root is benzene in such cases.
• Questions similar to page 16 about C-1 location and direction of numbering apply.
• Example solution: The complete IUPAC name is 1- chloro-4-ethyl-2-nitrobenzene.
• How should you add prefixes to complete the name? Arrange substituents alphabetically with their locator numbers preceding the root.

Page 18

• Disubstituted Benzenes: Ortho, Meta, and Para Designations:
  • Ortho = o = 1,2-positioning
  • Meta = m = 1,3-positioning
  • Para = p = 1,4-positioning

Page 19

• Phenyl and Benzyl Substituents:
  • It can be useful to treat a benzene ring as a substituent rather than as the root in a complex molecule.
  • Common examples:
  • C6H5: phenyl, abbreviated as Ph
  • C6H5CH2: phenylmethyl, also called benzyl, abbreviated as Bn

Page 20

• Examples of Phenyl and Benzyl Substituents:
  • Phenyl substituent leading to 3-Phenylhept-2-ene
  • Benzyl substituent shown as Ph–CH2–C6H5 arrangement
  • 1,4-Dibenzylcyclohexane as an example molecule