IUPAC Nomenclature

1) Quick Basics (GOC Context)

• Organic compounds: hydrocarbons and their derivatives.
• Types: Aliphatic (open chain) and Cyclic (ring chain).
• Saturated: only single bonds; Unsaturated: at least one double/triple bond.
• Homocyclic: ring has only carbon; Heterocyclic: ring has O/S/N etc.

2) Aromaticity (Hückel Rule)

• Aromatic compounds are planar, cyclic, conjugated with delocalised π electrons.
• Must follow Hückel rule: (4n + 2) π electrons (n = 0, 1, 2…)
• Typically resist addition and show electrophilic substitution.
• Aromatic heterocycles: rings with hetero atoms (e.g., pyridine, pyrrole, furan, thiophene).

3) Selecting the Parent Chain

• Choose the longest continuous carbon chain as parent.
• For unsaturated compounds, parent chain must include the double/triple bond even if it’s not the longest chain.
• For functional groups, choose a chain that includes the principal functional group.

4) Numbering Rules (Very Important)

• Lowest locant rule: the first substituent gets the lowest possible number.
• Lowest sum rule: when many substituents are present, choose numbering with the lowest sum of locants.
• First point of difference: if locant sets tie, pick the set with the lower number at the first point of difference.
• For alkenes/alkynes: give lowest number to the multiple bond (even if it violates saturated rules).
• For functional groups: give lowest number to the principal functional group.

5) Writing Substituents

• Write different substituents in alphabetical order (ignore di-, tri-, tetra- for ordering).
• Use numerical prefixes: di-, tri-, tetra- for identical substituents.
• Complex substituent (branched): name it separately, number from the point of attachment as 1′, and write in brackets.
• For repeated complex substituents use: bis-, tris-, tetrakis-.

6) Naming Unsaturated Hydrocarbons

• Use suffix: -ene (double bond), -yne (triple bond), -diene, etc.
• Number the chain so the double/triple bond gets the lowest locant.
• If both double and triple bonds exist, numbering generally prefers giving the double bond the lower number (common rule of thumb).

7) Functional Group Naming (Single FG)

• Select the functional group → it decides the class suffix.
• Number from the end nearer to the functional group so it gets the lowest locant.
• Terminal functional groups like -CHO, -COOH, -COOR, -CONH2, -CN are typically assigned carbon number 1.
• If multiple identical functional groups exist, use: di-, tri-, etc. (e.g., diol, dioic acid).

8) Priority Order (For Polyfunctional Compounds)

Pick one as the principal functional group (gets suffix). Others become prefixes.

9) Replacement Nomenclature (oxa / thia / aza)

• Used for naming chains/rings where hetero atoms replace carbon:
• O → oxa, S → thia, Se → selena, N → aza
• Give hetero atoms the lowest possible locants.

10) Alicyclic (Cyclo) Nomenclature

• Ring as parent if ring carbons ≥ side-chain carbons (common rule used in naming).
• Substituted cycloalkanes: assign numbers to give lowest set of locants; alphabetical order helps in ties.
• For cycloalkenes, the double bond gets priority in numbering.
• If side chain has a multiple bond or functional group, ring may be treated as substituent (rule used in many examples).

11) Bond-Line (Skeletal) Structures

• Each line end/vertex represents a carbon.
• Hydrogens on carbon are implied to satisfy valency (C makes 4 bonds).
• Hetero atoms (O, N, halogens) are shown explicitly.