Alcohols, Phenols and Ethers – Unit 7 Review

Flashcards covering classification, nomenclature, preparation, properties and reactions of alcohols, phenols and ethers, suitable for exam revision.

How are alcohols classified based on the number of –OH groups present?

As monohydric, dihydric, trihydric or polyhydric alcohols.

What hybridisation is found on the carbon bearing the –OH group in ordinary saturated alcohols?

sp3 hybridisation.

Define a primary alcohol.

An alcohol in which the –OH group is attached to a primary carbon (one bonded to only one other carbon).

Give the IUPAC suffix used for naming alcohols.

The suffix “-ol” (replaces the terminal ‘e’ of the parent alkane).

State Markovnikov’s rule as applied to acid-catalysed hydration of alkenes.

The –OH group attaches to the more substituted carbon of the double bond, and H to the less substituted carbon.

Which reagent combination represents hydroboration-oxidation?

(i) BH3·THF or B2H6, then (ii) H2O2/ NaOH.

What product is obtained when methanal reacts with a Grignard reagent followed by hydrolysis?

A primary alcohol.

Write the general formula of a Grignard reagent.

R–Mg–X, where X = Cl, Br or I.

Name the industrial route used to manufacture phenol from cumene.

The cumene hydroperoxide process (cumene → cumene hydroperoxide → phenol + acetone).

Which physical interaction gives alcohols much higher boiling points than ethers of comparable mass?

Intermolecular hydrogen bonding between –OH groups.

Why is methanol called “wood spirit”?

It was formerly obtained by destructive distillation of wood.

Give the Lucas test observation for tertiary alcohols.

Immediate turbidity when treated with Lucas reagent (conc. HCl + ZnCl2) at room temperature.

Arrange in order of increasing acid strength: ethanol, phenol, water.

Ethanol < water < phenol.

What is the conjugate base of phenol called?

Phenoxide ion (or phenolate ion).

State Kolbe’s reaction.

Sodium phenoxide reacts with CO2 (373 K, 4–7 atm) followed by acidification to give salicylic acid (o-hydroxybenzoic acid).

What is the final product of the Reimer–Tiemann reaction on phenol?

Salicylaldehyde (o-hydroxybenzaldehyde).

Give the formula of PCC and its main use with alcohols.

Pyridinium chlorochromate, used to oxidise primary alcohols to aldehydes without further oxidation to acids.

What happens when ethanol vapour is passed over hot Cu at 573 K?

It is dehydrogenated to ethanal (acetaldehyde).

Name the catalyst typically used for hydration of ethene to ethanol.

Conc. H2SO4 (two-step acid-catalysed process) or phosphoric acid on silica (industrial).

Define Williamson ether synthesis.

Reaction of an alkoxide/aryloxide ion with a primary alkyl halide (SN2) to form an ether and a halide ion.

Why are tertiary alkyl halides unsuitable in Williamson synthesis?

Because the strong basic alkoxide causes elimination (E2) to give an alkene rather than substitution.

Write the dehydration condition (temp, acid) that favours ether formation from ethanol.

Conc. H2SO4 at about 413 K.

Which electrophilic substitution positions are favoured in anisole?

Ortho and para positions relative to the –OCH3 group.

State the order of reactivity of hydrogen halides in cleaving ethers.

HI > HBr >> HCl.

What two molecules are formed when diethyl ether is treated with excess HI at high temperature?

2 CH3CH2I (ethyl iodide) and H2O.

Why does o-nitrophenol steam-distil but p-nitrophenol does not?

o-Nitrophenol has intramolecular H-bonding making it volatile; p-isomer forms intermolecular H-bonds leading to association and higher b.p.

Give one commercial use of methanol.

As a solvent and as a feedstock for formaldehyde production.

Name the enzyme that converts glucose to ethanol during fermentation.

Zymase.

What is denatured alcohol?

Ethanol rendered unfit for drinking by adding substances like CuSO4 and pyridine.

State the product when anisole reacts with bromine in acetic acid without FeBr3.

Mainly p-bromoanisole (with some o-bromoanisole).

How does branching affect the boiling point of alcohols?

Boiling point decreases with increased branching due to reduced surface area.

Which substance is obtained by acetylating salicylic acid?

Aspirin (acetylsalicylic acid).

Write the equation for oxidation of secondary alcohol with acidified K2Cr2O7.

R–CH(OH)–R' → R–CO–R' (ketone) + H2O.

Why are ethers less soluble in water than isomeric alcohols?

They lack –OH hydrogen and can only accept H-bonds, not donate, resulting in weaker interactions with water.

Give one distinguishing reaction between phenol and ethanol.

Phenol gives purple coloration with FeCl3; ethanol does not.

What is picric acid?

2,4,6-Trinitrophenol.

Define vinylic alcohol.

An alcohol in which –OH is attached to an sp2 carbon of an alkene (vinyl carbon).

Which alcohol does not undergo oxidation under normal conditions?

Tertiary alcohols.

Write the formula for tert-butoxide ion.

(CH3)3C–O–

Why is phenol more acidic than cyclohexanol?

Because the negative charge in phenoxide ion is stabilised by resonance with the aromatic ring.

Give the common name of CH3OCH3.

Dimethyl ether.

What is Lucas reagent made of?

Conc. HCl and anhydrous ZnCl2.

Explain the term ‘unsymmetrical ether’.

An ether in which the two alkyl/aryl groups on oxygen are different, e.g., CH3OC2H5.

Which product forms when methoxymethane reacts with excess HI?

2 molecules of methyl iodide (CH3I) and water.

What is produced when phenol is heated with Zn dust?

Benzene.

Which reagent converts an alcohol directly to a bromide?

PBr3 or HBr (with acid).

Define allylic alcohol.

An alcohol where the –OH is attached to an sp3 carbon adjacent to a C=C bond.

Give the pKa of phenol approximately.

About 10.0.

What is the directing effect of –OH on an aromatic ring?

It is ortho/para-directing due to electron donation via resonance.

State the product of nitration of phenol with dilute HNO3 at 298 K.

A mixture of o-nitrophenol and p-nitrophenol.

What happens to phenol in air over time?

It slowly oxidises to dark-coloured quinones.

Which catalyst is used for large-scale methanol synthesis from CO and H2?

ZnO-Cr2O3 catalyst.

Why is HI able to cleave ethers more readily than HCl?

HI is more acidic and I− is a much better nucleophile than Cl−.

Describe the rearrangement in dehydration of 2-methyl-1-butanol.

Formation of a secondary carbocation via hydride shift before elimination, leading to 2-methyl-2-butene as major alkene.

How can benzyl chloride be converted to benzyl alcohol?

By aqueous hydrolysis (SN1) or reaction with moist Ag2O.

What test distinguishes primary, secondary and tertiary alcohols rapidly?

Lucas test (rate of turbidity with Lucas reagent).

Which ether has the common name ‘ethyl methyl ether’?

CH3OCH2CH3.

Explain why phenols do not undergo nucleophilic substitution with HX to give aryl halides.

Because the C–O bond in phenol has partial double-bond character and the sp2 carbon cannot support SN1 or SN2 displacement by halide.

Write the product of Friedel–Crafts acetylation of anisole.

Mainly p-methoxyacetophenone (with some o-isomer).

How can cyclohexanol be dehydrated to cyclohexene? (Give conditions.)

Heat with conc. H3PO4 or H2SO4 at about 443 K.

State the main limitation of Williamson synthesis.

It fails with bulky (secondary/tertiary) alkyl halides due to competing elimination.

What property makes sodium ethoxide a stronger base than sodium hydroxide?

The ethoxide ion (RO−) is less stable than OH− due to the electron-releasing alkyl group, hence it is a stronger base.

Give the molecular formula of glycerol.

C3H8O3.