Alcohols, Phenols and Ethers
Class 12 · Chemistry
4 ideas in Class 12 Chemistry, explained in plain words, with games and quizzes to practise.
Families, Names and Hydrogen Bonding
Part of: Families, Names and Preparation
Hydroxy compounds split into monohydric, dihydric and trihydric by OH count, and into primary, secondary and tertiary by the crowding of the holder carbon; phenols carry OH on a ring, and ethers carry oxygen between two carbon groups (simple when both sides match, mixed when they differ). The bent shape around oxygen lets hydroxy compounds link into hydrogen-bond networks, lifting boiling points and water solubility, while ethers can only accept such links.
Why it matters. Names and families predict every later reaction, and hydrogen bonding explains at a glance why ethanol pours like water while dimethyl ether escapes as a gas.
Key words
- Monohydric compound
- : A molecule carrying exactly one hydroxy group.
- Primary hydroxy compound
- : OH holder carbon joined to only one other carbon.
- Phenol
- : A hydroxy group joined directly to a benzene ring.
- Simple ether
- : An ether with identical groups on both sides of oxygen.
- Mixed ether
- : An ether with different groups on the two sides of oxygen.
- Hydrogen bonding
- : A strong attraction between a hydrogen on O or N and a lone pair nearby.
Try it in two minutes
- Count the OH groups and study the holder carbon.
- Name the parent chain with the hydroxy position.
- Ask whether the molecule can donate hydrogen bonds.
Try at home. Rank methanol, ethanol, butan-1-ol and hexan-1-ol by water solubility and test the trend.
Making Hydroxy Compounds and Phenol
Part of: Families, Names and Preparation
Alkenes add water in acid by the Markovnikov pattern, while hydroboration-oxidation delivers OH to the less crowded carbon. Grignard reagents add to methanal, other aldehydes and ketones to give primary, secondary and tertiary products after hydrolysis, and LiAlH4 reduces carbonyls the same way. Phenol comes from cumene through its hydroperoxide, from diazonium salts with warm water, and from chlorobenzene with aqueous alkali at high temperature and pressure.
Why it matters. These routes let chemists place OH exactly where wanted, and the cumene path is how the world manufactures phenol.
Key words
- Markovnikov addition
- : Water or HX adding so OH or halogen lands on the more crowded carbon.
- Hydroboration-oxidation
- : A two-stage sequence placing OH on the less crowded carbon.
- Grignard addition
- : RMgX joining a carbonyl, then hydrolysis freeing a hydroxy compound.
- Cumene process
- : Phenol manufacture from isopropylbenzene via its hydroperoxide.
- Diazonium hydrolysis
- : Warming a diazonium salt with water to release phenol and nitrogen.
Try it in two minutes
- Spot the starting alkene, carbonyl or diazonium salt.
- Match the reagent to the wanted substitution pattern.
- Hydrolyse the intermediate to free the product.
Try at home. Write two different routes to propan-2-ol and pick the cleaner one.
Acidity and Reactions of Hydroxy Compounds
Part of: Acidity, Reactions and Ethers
Phenol out-acids water and hydroxy compounds because its anion spreads charge into the ring, while electron-withdrawing groups strengthen it further and alkyl groups weaken hydroxy acidity. Hydroxy compounds form alkoxides with active metals, esters with acids, alkenes on strong heating with acid, and carbonyls on oxidation: primary compounds stop at aldehydes with PCC but reach acids with strong oxidants, secondary ones halt at ketones, and tertiary ones resist.
Why it matters. Acidity order plus the 413 K versus 443 K dehydration split are among the most examined facts of organic chemistry.
Formulas
- Acidity order: phenol > water > hydroxy compounds
- Dehydration: 443 K gives the alkene, 413 K gives the ether
- Saytzeff rule: the more substituted alkene is the major product
- PCC halts primary compounds at aldehydes; strong oxidants reach acids
Key words
- Acidity order
- : Phenol beats water, which beats hydroxy compounds, as proton donors.
- Phenoxide ion
- : The resonance-calmed anion left after phenol loses its proton.
- Esterification
- : Acid plus hydroxy compound giving an ester and water.
- Dehydration
- : Acid-driven loss of water forming an alkene or an ether.
- PCC oxidation
- : A gentle oxidant halting primary compounds at the aldehyde stage.
- Lucas distinction
- : Speed of cloudiness with HCl and zinc chloride sorting tertiary, secondary, primary.
Try it in two minutes
- Rank the acids by anion stability.
- Read the temperature on a dehydration setup.
- Match the oxidant to how far oxidation may go.
Try at home. List ethanol, water and phenol from weakest to strongest acid with one reason each.
Phenol Reactions and Ethers
Part of: Acidity, Reactions and Ethers
Phenol activates its ring so strongly that bromine water drops 2,4,6-tribromophenol at once, dilute nitric acid gives ortho and para nitrophenols, and concentrated nitric acid pushes on to picric acid. With carbon dioxide under pressure phenol forms salicylic acid (Kolbe), and with chloroform and alkali it forms salicylaldehyde (Reimer-Tiemann). Ethers arise cleanly when an alkyl halide meets sodium alkoxide or phenoxide (Williamson), and strong HI or HBr cleaves ethers so the smaller alkyl piece becomes the iodide or bromide.
Why it matters. Williamson reagent choice and ether cleavage direction are classic reasoning questions, and salicylic acid links the chapter to aspirin.
Formulas
- Williamson route: alkyl halide plus sodium alkoxide gives ether plus salt
- Ether cleavage rule: the smaller alkyl group becomes the iodide
- Kolbe product: phenol plus CO2 gives salicylic acid
- Reimer-Tiemann product: phenol plus CHCl3 gives salicylaldehyde
Key words
- Kolbe reaction
- : Phenol plus carbon dioxide under pressure giving salicylic acid.
- Reimer-Tiemann reaction
- : Phenol plus chloroform and alkali giving salicylaldehyde.
- Williamson synthesis
- : Alkyl halide plus alkoxide or phenoxide building an ether.
- Picric acid
- : 2,4,6-trinitrophenol from phenol and concentrated nitric acid.
- Ether cleavage
- : Splitting of ethers by strong hydrogen halides on heating.
Try it in two minutes
- Read the directing power of the OH group.
- For an ether, pair an alkyl halide with an alkoxide, never an aryl halide.
- On cleavage, hand the halogen to the smaller alkyl piece.
Try at home. Plan ethoxybenzene from phenol in two written steps with reagents.
What your child will practise
- Acidity and Reactions of Hydroxy Compounds: Ocean Quick Fire (Quick Fire)
- Families, Names and Hydrogen Bonding: Jungle Puzzle (Clue Puzzle)
- Families, Names and Hydrogen Bonding: Jungle Quick Fire (Quick Fire)
- Making Hydroxy Compounds and Phenol: Candy Quick Fire (Quick Fire)
- Phenol Reactions and Ethers: Desert Puzzle (Clue Puzzle)
- Quiz: Acidity and Reactions of Hydroxy Compounds (8 questions)
- Quiz: Families, Names and Hydrogen Bonding (8 questions)
- Quiz: Making Hydroxy Compounds and Phenol (8 questions)
- Quiz: Phenol Reactions and Ethers (8 questions)