Definitions [1]
Nomenclature is the system of assignment of names to organic compounds.
Key Points
Classification of Alcohols
Based on number of —OH groups
| Type | —OH Groups | Example |
|---|---|---|
| Monohydric | 1 | Ethanol (CH₃CH₂OH) |
| Dihydric | 2 | Ethylene glycol (CH₂OH–CH₂OH) |
| Trihydric | 3 | Glycerol |
| Polyhydric | More than 3 | Glucose |
Based on hybridisation of carbon bearing —OH (Monohydric only):
| Type | Description | Example |
|---|---|---|
| Primary (1°) | —OH on primary carbon | R–CH₂–OH |
| Secondary (2°) | —OH on secondary carbon | R–CH(OH)–R |
| Tertiary (3°) | —OH on tertiary carbon | R–C(OH)(R)–R |
| Allylic | —OH on sp³ carbon next to C=C | CH₂=CH–CH₂OH |
| Vinylic | —OH directly on sp² carbon of C=C | CH₂=CH–OH |
| Benzylic | —OH on sp³ carbon next to aromatic ring | C₆H₅–CH₂–OH |
Classification of Phenols
| Type | —OH Groups | Example |
|---|---|---|
| Monohydric | 1 | Phenol |
| Dihydric | 2 | Catechol (Benzene-1,2-diol) |
| Trihydric | 3 | Phloroglucinol (Benzene-1,3,5-triol) |
Classification of Ethers
| Type | Description | Example |
|---|---|---|
| Simple / Symmetrical | Same alkyl/aryl groups on both sides of O | CH₃–O–CH₃ (Dimethyl ether), C₆H₅–O–C₆H₅ (Diphenyl ether) |
| Mixed / Unsymmetrical | Different alkyl/aryl groups on both sides of O | CH₃–O–C₂H₅ (Ethyl methyl ether), C₂H₅–O–C₆H₅ (Ethyl phenyl ether) |
- The IUPAC system provides a unique, systematic way to name carbon compounds based on structure, replacing confusing common names.
- An IUPAC name has three parts: prefix, parent, and suffix, reflecting the carbon chain and functional group.
- The parent name is based on the longest carbon chain, and its ending changes to –ane, –ene, or –yne depending on the number of bonds.
- Functional groups are shown as prefixes or suffixes, and the chain is numbered to give them the lowest possible number.
- If the suffix begins with a vowel, the final ‘e’ in the parent alkane name is dropped (e.g., propane → propanone).
-
Williamson Synthesis (most important): R–O–Na + X–R' → R–O–R' + NaX. Primary alkyl halide is preferred (SN2 mechanism; 2° or 3° alkyl halide gives elimination).
-
Acid-catalysed dehydration of alcohols:
\[\ce{2R - OH ->[H2SO4, 413K] R - O - R + H2O}\]
(works best for symmetrical ethers)
-
From alcohols by catalytic dehydration:
\[\ce{2C2H5OH ->[Al2O3, 513-523K] C2H5 - O - C2H5 + H2O}\]
-
Alkoxy mercuration-demercuration: \[\begin{array}{cc}
\phantom{}\ce{CH3 - CH = CH2 + C2H5OH + Hg(OCOCF3)2 -> CH3 - CH - CH2 - HgOCOCF3 ->[NaBH4/OH^{-}] CH3 - CH - CH3}\\
\phantom{................................................................................}|\phantom{.....................................................................}|\phantom{.}\\
\phantom{............................................................................................}\ce{OC2H5}\phantom{...........................................................}\ce{O-C2H5}\phantom{.}
\end{array}\]
