Overview
This lecture explains the key rules of IUPAC nomenclature for organic compounds, including how to identify the parent chain, number carbons, name substituents, and assign functional group priorities.
Steps for IUPAC Naming
- Identify the longest continuous carbon chain as the parent chain.
- Number the carbon chain from both ends and choose the direction that gives substituents and functional groups the lowest numbers.
- Base the stem name on the number of carbons (e.g., meth-, eth-, prop-, but-, pent-).
- Identify the types of bonds (single = -ane, double = -ene, triple = -yne) and use the correct suffix.
- For cyclic compounds, add the prefix "cyclo-" before the stem.
- For side chains and substituents, use prefixes with position numbers (e.g., 2-methylbutane).
- For multiple identical substituents, use prefixes like di-, tri-, and specify positions (e.g., 2,3-dimethylbutane).
- For halogens/alkyl groups, list them as prefixes and order alphabetically, ignoring di-/tri-.
- Separate numbers and letters with hyphens, and use commas for multiple numbers.
Functional Groups & Priority
- Functional groups often determine suffixes (e.g., -ol for alcohol, -al for aldehyde, -one for ketone, -oic acid for carboxylic acid).
- Include the functional group carbon in the chain count.
- When multiple functional groups or substituents exist, use the IUPAC priority list: acids (COOH) > aldehydes > ketones > alcohols > double/triple bonds > halogens > alkyl groups.
- Assign numbering to give the highest-priority group the lowest number.
Examples & Special Cases
- The presence of double/triple bonds: specify their positions (e.g., but-2-ene, pent-1,3-diyne).
- Alcohols are named with -ol, remove the 'e' (e.g., butan-2-ol).
- For aldehydes and carboxylic acids, position 1 is assumed and not numbered unless required.
- For ketones, the functional group location must be specified if more than three carbons (e.g., butan-2-one).
- Always verify the longest possible chain, especially in branched structures.
Key Terms & Definitions
- Prefix — part of the name added before the parent chain, for substituents.
- Suffix — part of the name added after the parent chain, often signifying functional groups.
- Parent Chain — longest continuous chain of carbon atoms.
- Substituent — an atom or group replacing hydrogen on the parent chain.
- Functional Group — an atom or set giving characteristic properties, determines suffix and priority.
- IUPAC — International Union of Pure and Applied Chemistry, the body that standardizes chemical nomenclature.
Action Items / Next Steps
- Practice naming organic compounds using the rules discussed.
- Try the quiz and top three questions on IUPAC naming (links provided below the lecture video).
- Make your own summary of the IUPAC rules for quick revision.