IUPAC System of Nomenclature — Revision Notes

⚡ 30-Second Revision

Root Word: — Number of C atoms (meth-, eth-, prop-, but-, pent-, hex-).
Primary Suffix: — C-C bond type (-ane, -ene, -yne).
Secondary Suffix: — Principal functional group (-ol, -al, -one, -oic acid, -amine).
Prefixes: — Substituents (methyl, chloro, hydroxy, oxo) & cyclic ('cyclo-').
Locants: — Numbers for positions, lowest for principal FG.
Priority Order (High to Low): — COOH > -COOR > -CONH$_2$ > -CHO > C=O > -OH > -NH$_2$ > C=C > C≡C.
Alphabetical Order: — For substituents (ignore di, tri, tetra).
Punctuation: — Hyphens for numbers-letters, commas for numbers-numbers.

2-Minute Revision

IUPAC nomenclature provides a systematic way to name organic compounds. Start by identifying the longest continuous carbon chain (root word). Then, determine the saturation of this chain using the primary suffix (-ane, -ene, -yne).

Next, identify the principal functional group based on priority rules and assign its secondary suffix (-ol, -al, -one, -oic acid). Number the parent chain to give the principal functional group the lowest possible locant.

If no functional group, prioritize multiple bonds, then substituents. Any other groups are named as secondary prefixes (e.g., methyl, chloro, hydroxy) and listed alphabetically with their locants.

For cyclic compounds, add 'cyclo-' as a primary prefix. Remember to use hyphens and commas correctly. For ethers, use 'alkoxyalkane' where the smaller alkyl group forms the 'alkoxy' part. Mastering functional group priority and systematic chain numbering are critical for NEET success.

5-Minute Revision

Mastering IUPAC nomenclature is essential for NEET. Begin by understanding the five core components of an IUPAC name: secondary prefix, primary prefix, root word, primary suffix, and secondary suffix.

The root word is derived from the longest continuous carbon chain. For example, a 5-carbon chain is 'pent-'. The primary suffix indicates the type of carbon-carbon bonds: '-ane' for single, '-ene' for double, '-yne' for triple.

The secondary suffix denotes the principal functional group, determined by a strict priority order (e.g., carboxylic acid > aldehyde > ketone > alcohol). For instance, an alcohol uses '-ol'.

Numbering the chain is crucial: always assign the lowest possible locant to the principal functional group. If there's no principal functional group, prioritize multiple bonds, then substituents. For multiple substituents, list them alphabetically, ignoring multiplying prefixes like 'di-' or 'tri-'. For example, 'ethyl' comes before 'methyl'. Use locants (numbers) to indicate positions, separated by hyphens from letters and commas from other numbers.

Example 1: $ ext{CH}_3 ext{CH}( ext{OH}) ext{CH}_2 ext{CH}_3$

1
Longest chain: 4 carbons (but-).
2
Functional group: -OH (alcohol), suffix '-ol'.
3
Numbering: From right, -OH is at C-2 (lowest). From left, -OH is at C-3. So, C-2.
4
Name: Butan-2-ol.

Example 2: $ ext{CH}_3 ext{CH}( ext{Cl}) ext{CH}_2 ext{CHO}$

1
Principal functional group: Aldehyde (-CHO), suffix '-al'. Its carbon is C-1.
2
Longest chain: 4 carbons (but-).
3
Substituent: Chloro (-Cl) at C-3.
4
Name: 3-chlorobutanal.

Remember specific rules for ethers (alkoxyalkane) and cyclic compounds (e.g., cyclohexanecarbaldehyde for -CHO directly on a ring). Consistent practice with diverse examples is the best way to solidify these rules and avoid common pitfalls.

Prelims Revision Notes

IUPAC nomenclature is the systematic naming of organic compounds. It follows a 'prefix-root-suffix' structure.

1. Root Word: Indicates the number of carbons in the longest continuous chain (parent chain). * 1C: Meth-, 2C: Eth-, 3C: Prop-, 4C: But-, 5C: Pent-, 6C: Hex-, etc.

2. Primary Suffix: Describes C-C bond saturation. * Single bonds: -ane * Double bonds: -ene (use diene, triene for multiple) * Triple bonds: -yne (use diyne, triyne for multiple)

3. Secondary Suffix: Denotes the principal functional group. Drop 'e' from primary suffix if secondary suffix starts with a vowel. * Carboxylic acid (-COOH): -oic acid * Ester (-COOR): -oate (alkyl alkanoate) * Acid halide (-COX): -oyl halide * Amide (-CONH$_2$): -amide * Nitrile (-C≡N): -nitrile * Aldehyde (-CHO): -al * Ketone (C=O): -one * Alcohol (-OH): -ol * Thiol (-SH): -thiol * Amine (-NH$_2$): -amine

4. Prefixes:

* Primary Prefix: 'cyclo-' for cyclic compounds. * Secondary Prefixes: For substituents or non-principal functional groups. * Alkyl groups: methyl, ethyl, propyl, isopropyl, etc. * Halogens: fluoro, chloro, bromo, iodo * Other common groups: hydroxy (-OH), amino (-NH$_2$), nitro (-NO$_2$), alkoxy (-OR), oxo (=O, for ketone/aldehyde when not principal FG).

5. Numbering Rules (Locants):

* Number the parent chain to give the principal functional group the lowest possible locant. * If no principal functional group, prioritize multiple bonds (lowest locant). * If only substituents, number to give the lowest sum of locants. If sums are equal, prioritize alphabetically for the first point of difference.

6. Alphabetical Order: List different substituents alphabetically (e.g., bromo before chloro). Ignore multiplying prefixes (di-, tri-, tetra-) for alphabetical sorting, but consider 'iso' and 'neo' (e.g., isopropyl, neopentyl).

7. Punctuation: Use hyphens (-) to separate numbers from letters. Use commas (,) to separate numbers from numbers. The entire name is written as one word.

Functional Group Priority Order (Decreasing):

-COOH > -SO$_3$H > -COOR > -COX > -CONH$_2$ > -CN > -CHO > C=O > -OH > -SH > -NH$_2$ > C=C > C≡C > -OR > -X > -NO$_2$ > Alkyl.

Special Cases:

Ethers: — Named as 'alkoxyalkane'. Smaller alkyl group becomes 'alkoxy' prefix.
Aldehydes/Carboxylic Acids on Rings: — If -CHO or -COOH is directly attached to a ring, use suffixes '-carbaldehyde' or '-carboxylic acid' respectively.

Vyyuha Quick Recall

To remember the functional group priority order (highest to lowest for common groups):

Can Every Apple Always Keep An Always Elegant Yak?

Carboxylic acid (-COOH)
Ester (-COOR)
Amide (-CONH$_2$)
Aldehyde (-CHO)
Ketone (C=O)
Alcohol (-OH)
Amine (-NH$_2$)
Ene (C=C)
Yne (C≡C)