MHT-CET Chemistry · Alcohols, Phenols and Ethers

IUPAC and Common Nomenclature of Alcohols, Phenols and Ethers

Alcohols are named three ways — carbinol (the C–OH carbon is 'carbinol', its groups are prefixes), common (tert-butyl alcohol) and IUPAC (-ol with the lowest locant); phenols have six common names to memorise against their benzene-diol/triol IUPAC names; ethers are alkoxyalkanes.

All Alcohols, Phenols and Ethers notes MHT-CET Chemistry strategy

Why this matters

35 PYQs, 1 HARD — the largest page in the chapter and the most reliable mark. Thirteen are the named phenols in either direction (catechol ↔ benzene-1,2-diol and the rest), fifteen are an IUPAC name read off a drawn cyclopentanol, cyclobutane ether or alkenol, five are carbinol names, two are isomer pairs. One table, one naming routine.

Concept 1 of 4

Carbinol Names and the Butyl Alcohols

Intuition

In the carbinol system methanol is 'carbinol' and every other alcohol is carbinol with its alkyl groups as prefixes, named alphabetically. Count the groups on the C–OH carbon: isopropyl alcohol has two methyls — dimethyl carbinol; tert-butyl alcohol three — trimethyl carbinol; sec-butyl alcohol a methyl and an ethyl — ethyl methyl carbinol; isobutyl alcohol one isopropyl — isopropyl carbinol.

Definition

Methyl carbinol = ethanol; dimethyl carbinol = isopropyl alcohol (propan-2-ol); trimethyl carbinol = tert-butyl alcohol (2-methylpropan-2-ol).
Ethyl methyl carbinol = sec-butyl alcohol (butan-2-ol); isopropyl carbinol = isobutyl alcohol (2-methylpropan-1-ol); propyl carbinol = butan-1-ol.
The four butyl alcohols: n-butyl (butan-1-ol, 1°), isobutyl (2-methylpropan-1-ol, 1°), sec-butyl (butan-2-ol, 2°), tert-butyl (2-methylpropan-2-ol, 3°).
Groups on the carbinol carbon are listed alphabetically: ethyl before methyl.

Carbinol rule

\text{R}_1\text{R}_2\text{R}_3\text{C-OH} \to \text{(R}_1\text{ R}_2\text{ R}_3\text{) carbinol, alphabetical}

Worked example

Name pentan-3-ol and 2-methylbutan-2-ol in the carbinol system.

Practice this conceptself-check · 4 quick reps

From the bank · past-year question

Example 1Alcohols, Phenols and EthersEASY

According to carbinol system tert-butyl alcohol is named as

[Q71 · 15th May Shift 2 · 2023]

Naming isobutyl alcohol 'isobutyl carbinol'

The carbinol carbon is the CH₂OH; what hangs on it is an ISOPROPYL group. Isobutyl carbinol would be a five-carbon alcohol.

Drill 4 more on carbinol names and the butyl alcohols

Concept 2 of 4

The Named Phenols: Common Name ↔ IUPAC Name

Intuition

Six benzene polyols and the cresols carry names the paper uses interchangeably with the IUPAC locants. The diols run ortho, meta, para — catechol, resorcinol, quinol; the triols 1,2,3 and 1,3,5 — pyrogallol and phloroglucinol. o-Cresol is 2-methylphenol, not a triol. A substituted phenol is named as a phenol: 4-bromophenol, not 1-bromo-4-hydroxybenzene — unless a higher group (COOH) is present, when OH becomes 'hydroxy'.

Definition

Catechol = benzene-1,2-diol · resorcinol = benzene-1,3-diol · quinol (hydroquinone) = benzene-1,4-diol.
Pyrogallol = benzene-1,2,3-triol · phloroglucinol = benzene-1,3,5-triol · o-cresol = 2-methylphenol.
Glycerol ('propylene glycerol') = propane-1,2,3-triol; ethylene glycol = ethane-1,2-diol.
Phenol as parent: 4-bromophenol. Acid outranks OH: 3-ethyl-5-hydroxybenzoic acid (locants tie at {3,5}; ethyl before hydroxy alphabetically).

Common name	IUPAC name	OH positions
Catechol	Benzene-1,2-diol	ortho
Resorcinol	Benzene-1,3-diol	meta
Quinol (hydroquinone)	Benzene-1,4-diol	para
Pyrogallol	Benzene-1,2,3-triol	adjacent three 1,2,3 — not 1,3,5.
Phloroglucinol	Benzene-1,3,5-triol	alternate three
o-Cresol	2-Methylphenol	OH + CH₃ ortho The planted wrong pairing is 'o-cresol : benzene-1,2,3-triol'.
Glycerol	Propane-1,2,3-triol	—

Diols: cat-ortho, res-meta, quin-para. Triols: pyro-1,2,3, phloro-1,3,5.

Practice this conceptself-check · 4 quick reps

From the bank · past-year question

Example 2Alcohols, Phenols and EthersEASY

Which of the following is IUPAC name of hydroquinone?

[Q70 · 4th May Shift 2 · 2023]

Swapping pyrogallol and phloroglucinol

Both are triols. Pyrogallol's three OH are ADJACENT (1,2,3); phloroglucinol's alternate (1,3,5). The two are always offered together.

Drill 12 more on the named phenols: common name ↔ iupac name

Concept 3 of 4

IUPAC Names From a Drawing: Ring Alcohols, Ring Ethers, Alkenols

Intuition

For a ring alcohol the OH carbon is C1 and the ring is numbered the way that gives the substituents the lowest set of locants — so ethyl and methyl on the two carbons flanking C1 are 2-ethyl-5-methyl, not 2-ethyl-3-methyl. For a ring ether the alkoxy group is a prefix like any other, and the lowest-locant SET wins: 3-methoxy-1,1-dimethylcyclobutane {1,1,3} beats 1-methoxy-3,3-dimethyl {1,3,3}. For an alkenol, OH takes the lowest locant, then the double bond.

Definition

Cyclopentanol with ethyl and methyl on the carbons either side of C–OH: 2-ethyl-5-methylcyclopentanol (from C1 go towards ethyl, the alphabetical first). Both on the same side (2 and 3): 2-ethyl-3-methylcyclopentanol.
Cyclopentanol with methyls on both flanking carbons: 2,5-dimethylcyclopentanol. A methyl across the ring: 3-methylcyclopentanol.
Cyclobutane with OCH₃ and a gem-dimethyl opposite: 3-methoxy-1,1-dimethylcyclobutane. Ethyl and methyl flanking a cyclobutanol: 2-ethyl-4-methylcyclobutanol.
$\text{CH}_3\text{CH}_2\text{CH(CH}_3)\text{CH=CHCH(OH)CH}_2\text{CH}_3$ : OH first → 6-methyloct-4-en-3-ol. Crotonyl alcohol in bond-line: a four-carbon zigzag, C=C between C2 and C3, OH at the end (but-2-en-1-ol).
Open chain ether: $\text{CH}_3\text{OCH}_2\text{C(CH}_3)_2\text{CH}_2\text{CH}_3$ = 1-methoxy-2,2-dimethylbutane. Propan-1-ol in bond-line: three carbons, OH at the end.

Locant rules

\text{OH carbon} = \text{C1} \to \text{lowest locant SET for substituents} \to \text{alphabetical tie-break}

Worked example

Name a cyclohexanol carrying a methyl on C2 and a chlorine on C4 (numbered away from the methyl), and the alkenol

\text{CH}_2\text{=CH-CH(OH)-CH}_2\text{CH}_3

Practice this conceptself-check · 4 quick reps

From the bank · past-year question

Example 3Alcohols, Phenols and EthersMODERATE

What is IUPAC name of following compound?

[Q58 · 16th May Shift 2 · 2023]

Numbering the ring the short way

Going from C1 towards the methyl gives 2-methyl-5-ethyl — same locant set, wrong alphabetical order. The 2023 paper keyed 2-ethyl-3-methyl for a drawing with the groups on the same side and 2-ethyl-5-methyl for one with them on opposite sides; look at the drawing, not the option you remember.

Drill 14 more on iupac names from a drawing: ring alcohols, ring ethers, alkenols

Concept 4 of 4

Isomer Pairs: Alcohol–Ether, Position, Metamers

Intuition

An alcohol and an ether of the same formula are functional isomers (butan-1-ol and 1-methoxypropane, both ( ext{C}_4 ext{H}_{10} ext{O})). Two ethers of the same formula with the alkyls redistributed are metamers (ethoxyethane and methoxypropane). A pair with DIFFERENT formulas is no pair of isomers at all — methoxyethane is ( ext{C}_3 ext{H}_8 ext{O}), ethoxyethane ( ext{C}_4 ext{H}_{10} ext{O}).

Definition

Functional: butan-1-ol / 1-methoxypropane; ethanol / methoxymethane.
Metamerism: ethoxyethane / methoxypropane (both $\text{C}_4\text{H}_{10}\text{O}$ ); 1-methoxypropane / ethoxyethane.
Position: butan-1-ol / butan-2-ol; 1-methoxypropane / 2-methoxypropane. Chain: butan-2-ol / 2-methylpropan-1-ol.
NOT isomers: methoxyethane and ethoxyethane (different formulas).

Same formula, or no isomerism

\text{C}_4\text{H}_{10}\text{O}: \text{ butanols (alcohol)} \leftrightarrow \text{ethoxyethane / methoxypropane (ethers)}

Worked example

Which of these is NOT an isomer pair: pentan-1-ol and 1-ethoxypropane; 2-methoxypropane and 1-methoxypropane; propan-1-ol and ethoxyethane?

Practice this conceptself-check · 4 quick reps

From the bank · past-year question

Example 4Alcohols, Phenols and EthersEASY

Which among the following is NOT a pair of isomers?

[Q89 · 4th May Shift 2 · 2023]

Assuming any two ethers are metamers

Metamers must share a molecular formula. Methoxyethane (C₃) and ethoxyethane (C₄) differ by a CH₂ — homologues, not isomers of any kind.

Drill 1 more on isomer pairs: alcohol–ether, position, metamers

Summary — formulas & gotchas at a glance

A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.

Formulas (3)

Carbinol Names and the Butyl Alcohols
Carbinol rule
$\text{R}_1\text{R}_2\text{R}_3\text{C-OH} \to \text{(R}_1\text{ R}_2\text{ R}_3\text{) carbinol, alphabetical}$
IUPAC Names From a Drawing: Ring Alcohols, Ring Ethers, Alkenols
Locant rules
$\text{OH carbon} = \text{C1} \to \text{lowest locant SET for substituents} \to \text{alphabetical tie-break}$
Isomer Pairs: Alcohol–Ether, Position, Metamers
Same formula, or no isomerism
$\text{C}_4\text{H}_{10}\text{O}: \text{ butanols (alcohol)} \leftrightarrow \text{ethoxyethane / methoxypropane (ethers)}$

Reference tables (1)

The Named Phenols: Common Name ↔ IUPAC Name7 rows

Common name	IUPAC name	OH positions
Catechol	Benzene-1,2-diol	ortho
Resorcinol	Benzene-1,3-diol	meta
Quinol (hydroquinone)	Benzene-1,4-diol	para
Pyrogallol	Benzene-1,2,3-triol	adjacent three 1,2,3 — not 1,3,5.
Phloroglucinol	Benzene-1,3,5-triol	alternate three
o-Cresol	2-Methylphenol	OH + CH₃ ortho The planted wrong pairing is 'o-cresol : benzene-1,2,3-triol'.
Glycerol	Propane-1,2,3-triol	—

Diols: cat-ortho, res-meta, quin-para. Triols: pyro-1,2,3, phloro-1,3,5.

Watch out for (4)

Naming isobutyl alcohol 'isobutyl carbinol'
→ Carbinol Names and the Butyl Alcohols
Swapping pyrogallol and phloroglucinol
→ The Named Phenols: Common Name ↔ IUPAC Name
Numbering the ring the short way
→ IUPAC Names From a Drawing: Ring Alcohols, Ring Ethers, Alkenols
Assuming any two ethers are metamers
→ Isomer Pairs: Alcohol–Ether, Position, Metamers

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