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Must-know facts
23 facts
- 01Alcohol: –OH on sp³ carbon; phenol: –OH on an aromatic sp² carbon; vinylic alcohol: –OH on a C=C carbon. Allylic and benzylic alcohols are sp³ and can be 1°, 2° or 3°.
- 02Catechol, resorcinol, hydroquinone = benzene-1,2-, 1,3- and 1,4-diol; cresols = methylphenols; anisole = methoxybenzene; phenetole = ethoxybenzene.
- 03C–O–H angle slightly below 109°28′ (lone pairs); phenol C–O 136 pm (partial double bond); ether C–O–C angle slightly above tetrahedral, C–O 141 pm.
- 04Acid-catalysed hydration follows Markovnikov; hydroboration–oxidation gives the anti-Markovnikov-looking alcohol (propene → propan-1-ol).
- 05Grignard + methanal → 1° alcohol; + other aldehyde → 2°; + ketone → 3°.
- 06Aldehyde → 1° alcohol, ketone → 2° alcohol with H₂/Pt, Pd, Ni, NaBH₄ or LiAlH₄; acids need LiAlH₄ (industry: ester + H₂).
- 07Phenol routes: chlorobenzene + NaOH at 623 K, 320 atm; benzenesulphonic acid + molten NaOH; diazonium salt (273–278 K) + warm water; cumene → hydroperoxide → phenol + acetone.
- 08Boiling point rises with carbon number, falls with branching; hydrogen bonding puts alcohols far above ethers and alkanes of similar mass.
- 09pKa: p-nitrophenol 7.1 < o-nitrophenol 7.2 < m-nitrophenol 8.3 < phenol 10.0 < cresols 10.1–10.2 < ethanol 15.9 (acidity runs the other way).
- 10Alcohol acidity 1° > 2° > 3°; alcohols are weaker acids than water; alkoxide is a stronger base than hydroxide.
- 11Esterification with acid chlorides uses pyridine to remove HCl; salicylic acid acetylated → aspirin.
- 12Lucas reagent = conc. HCl + ZnCl₂: 3° alcohol turbid at once, 1° not turbid at room temperature.
- 13Dehydration ease 3° > 2° > 1°; carbocation formation is the slow step; ethanol + conc. H₂SO₄ → ethene at 443 K, ethoxyethane at 413 K.
- 14Oxidation: 1° → aldehyde (CrO₃ anhydrous or PCC) → acid (acidified KMnO₄); 2° → ketone (CrO₃); 3° resists. Cu at 573 K: 1° → aldehyde, 2° → ketone, 3° → alkene.
- 15Dilute HNO₃ (298 K) → o- + p-nitrophenol, separated by steam distillation (ortho is volatile, intramolecular H-bond).
- 16Bromine water + phenol → white 2,4,6-tribromophenol; Br₂ in CHCl₃ or CS₂ at low temperature → monobromophenols.
- 17Kolbe: sodium phenoxide + CO₂ → ortho-hydroxybenzoic acid. Reimer–Tiemann: CHCl₃ + NaOH → salicylaldehyde.
- 18Phenol + Zn dust → benzene; phenol + chromic acid → benzoquinone.
- 19Methanol: CO + H₂ over ZnO–Cr₂O₃, b.p. 337 K, poisonous. Ethanol: invertase then zymase, stops at 14%, b.p. 351 K; denatured with CuSO₄ + pyridine.
- 20Williamson: R–X + NaOR′ by SN2; use a primary halide. CH₃ONa + (CH₃)₃CBr gives only 2-methylpropene.
- 21b.p.: n-pentane 309.1 K, ethoxyethane 307.6 K, butan-1-ol 390 K; solubility 7.5 g vs 9 g per 100 mL water.
- 22Ether cleavage by HX: HI > HBr > HCl; halide attacks the smaller group (SN2) unless one group is tertiary (SN1). Anisole + HI → phenol + CH₃I.
- 23Anisole + Br₂ in ethanoic acid (no FeBr₃) → para-bromoanisole in 90% yield.
Common traps
Where marks are lost
Formulas
4 to know
pKa and Ka
pKa = −log Ka; Ka ratio = 10^(ΔpKa)
Phenol vs ethanol: ΔpKa = 15.9 − 10.0 = 5.9, ratio ≈ 7.9 × 10⁵.
Fermentation
C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂
Zymase in yeast; anaerobic; zymase stops above 14% alcohol.
Williamson synthesis
R–X + R′–O⁻Na⁺ → R–O–R′ + NaX
SN2; primary halide gives the ether, tertiary halide gives the alkene.
Cumene process
C₆H₅CH(CH₃)₂ + O₂ → C₆H₅C(CH₃)₂OOH; then H⁺/H₂O → C₆H₅OH + CH₃COCH₃
Air oxidation, then dilute acid.
Key terms
12 terms
- Monohydric / polyhydric
- Having one –OH group / many –OH groups.
- Allylic alcohol
- –OH on the sp³ carbon next to a C=C.
- Benzylic alcohol
- –OH on the sp³ carbon joined to an aromatic ring.
- Vinylic alcohol
- –OH on one of the sp² carbons of a C=C.
- Symmetrical ether
- An ether whose two groups on oxygen are the same.
- Hydroboration–oxidation
- Diborane addition to an alkene followed by H₂O₂/NaOH, giving the anti-Markovnikov-looking alcohol.
- Phenoxide ion
- C₆H₅O⁻, the conjugate base of phenol, stabilised by resonance with the ring.
- Lucas reagent
- Concentrated HCl with ZnCl₂, used to tell 1°, 2° and 3° alcohols apart.
- PCC
- Pyridinium chlorochromate, a CrO₃–pyridine–HCl complex that stops at the aldehyde.
- Denatured alcohol
- Ethanol made undrinkable with copper sulphate and pyridine.
- Williamson synthesis
- Ether formation from an alkyl halide and an alkoxide or phenoxide.
- Picric acid
- 2,4,6-Trinitrophenol, a strong acid.