Alkane Naming Rules and Strategies

Overview

This lecture covers the rules and strategies for naming alkanes, including parent chains, substituents, and naming conventions for both straight-chain and cyclic alkanes.

Alkane Basics

• Alkanes contain only carbon and hydrogen atoms, with all single bonds and no functional groups.
• The longest continuous chain of carbon atoms is called the parent chain.
• The parent chain's name is based on the number of carbons, using specific prefixes and the suffix -ane.

Alkane Parent Chain Naming

• 1 C: methane; 2 C: ethane; 3 C: propane; 4 C: butane; 5 C: pentane; 6 C: hexane; 7 C: heptane; 8 C: octane; 9 C: nonane; 10 C: decane; 11 C: undecane; 12 C: dodecane.
• Use the mnemonic "Me Eat Peanut Butter" to remember methyl, ethyl, propyl, butyl for 1–4 carbon substituents.

Substituent Naming Rules

• Branches (substituents) are named with the same prefixes but use the suffix -yl (e.g., methyl, ethyl).
• Name and number all substituents before the parent chain name.
• Use hyphens to separate numbers and letters; use commas to separate multiple numbers.

Numbering the Parent Chain

• Number the parent chain so substituents have the lowest possible numbers.
• If there's a tie, choose the path that gives more substituents off the chain.
• For multiple substituents, list their locations using numbers and group identical substituents with prefixes (di-, tri-, etc.).

Alphabetical Order and Naming Multiple Substituents

• List substituents alphabetically, ignoring prefixes like di-, tri-.
• Assign numbers to each substituent; if multiples occur at the same carbon, repeat the locator number.

Naming Cycloalkanes

• Cycloalkanes are rings; add the prefix "cyclo-" to the parent name (e.g., cyclohexane).
• For a single substituent, number it as position 1 and omit the number in the name.
• For multiple substituents, number to give the lowest set of numbers, and use the alphabet to break ties.
• Always include the "cyclo-" prefix and name substituents before the parent name.

Special Cases: Rings as Substituents

• If a straight chain is longer than the ring, the straight chain is the parent.
• Name the ring as a substituent (e.g., cyclobutyl), giving its location on the parent chain.

Halogen Substituents

• Halogen substituents are named by replacing the ending with -o (fluoro, chloro, bromo, iodo).
• Always list halogens as substituents with their locators.

Key Terms & Definitions

• Alkane — A hydrocarbon containing only single bonds.
• Parent Chain — The longest continuous chain of carbons in a molecule.
• Substituent — A group attached to the parent chain, named with a -yl ending.
• Cycloalkane — An alkane forming a ring structure, named with a "cyclo-" prefix.
• Chain Locator — The number indicating a substituent’s position on the parent chain.
• Alphabetical Order — The process for ordering different substituents in a name.

Action Items / Next Steps

• Memorize the name and number prefixes for 1–12 carbons.
• Practice identifying parent chains and numbering them for the lowest substituent positions.
• Complete any assigned homework or practice problems on naming alkanes.