Most Important Alcohols And Phenols MCQs with Answers

The best reagent for converting alcohols into aldehydes and ketones is acid dichromate.

Tertiary alcohols are resistant to oxidation and instead undergo elimination reactions to give alkenes in the presence of acid dichromate.

C₂H₅OH + PCl₅ → C₂H₅Cl + POCl₃ + HCl. Phosphorus pentachloride reacts with ethanol to produce ethyl chloride.

Ethanol reacts with concentrated H₂SO₄ at 180°C to give ethene (CH₂=CH₂) and water.

Lower alcohols are readily soluble in water.

The solubility of alcohols is due to hydrogen bonding, which is prominent in lower alcohols.

Melting and boiling points of alcohols are higher than corresponding alkanes.

This is also due to hydrogen bonding which is present in alcohols but absent in alkanes.

Primary alcohols, like ethanol, form an oily layer only on heating with the Lucas reagent (anhydrous ZnCl₂).

Ethanol gives iodoform with iodine in the presence of NaOH, indicated by the formation of yellow crystals.

Ethanol gives the iodoform test, while methanol does not, providing a chemical distinction.

Formerly, methanol was prepared by distillation of wood, which is why it is also called wood spirit.

The optimum temperature for the process of fermentation is 25-35°C.

Alcohol obtained by fermentation is only up to 12% and never exceeds 14% because beyond this limit enzymes become inactive.

Alcohol obtained by fermentation is distilled again and again to obtain 95% alcohol which is called rectified spirit.

Absolute alcohol can also be obtained by redistillation of rectified spirit in the presence of Calcium oxide (CaO), which absorbs its moisture.

Aromatic compounds which contain one or more OH groups directly attached with carbon of benzene ring are called Phenols.

The simplest example is phenol, which is also known as Carbolic acid (C₆H₅OH).

Phenol was first obtained from coaltar by Runge in 1834.

Alcohols, phenols, and ethers are classes of organic compounds which are much closer to water in structure and hence considered as derivatives of water.

Both contain hydroxyl (-OH) group so they may also be termed as hydroxy derivatives of alkanes and benzene respectively.

Phenols have the -OH group directly attached to a benzene ring, while aliphatic alcohols have it attached to an alkyl group.

The simplest example is phenol which is also known as Carbolic acid i.e. C₆H₅OH.

Phenol is also known as Carbolic acid.

Phenol is a colourless, crystalline, deliquescent solid with characteristic phenolic odour having melting point 41°C.

Phenol is sparingly soluble in water forming pink solution at room temperature but completely soluble above 68.5°C.

Phenol is poisonous and used as a disinfectant in hospitals and washrooms.

Phenol shows two types of reactions: 1. Reactions due to -OH group, 2. Reactions due to benzene ring.

Phenols are less reactive to nucleophiles so nucleophilic attack is less favoured.

Electrophilic attack on the ring is easy.

Phenol is much more acidic than alcohols but less acidic than carboxylic acids.

Phenol dissolves readily in alkalies but it is too weak to affect the litmus paper or to evolve CO₂ from carbonates.

Phenol is partially soluble in water and its solution has a pH of around 5 or 6.

The reason why phenol is acidic lies in the nature of the phenoxide ion. The negative charge on oxygen atom can become involved with the π-electron cloud on the benzene ring, leading to delocalization and stabilization of the phenoxide ion.

Phenol reacts with acetyl chloride in the presence of a base to form ester (Phenyl acetate).

When phenol is reduced with Zn, it forms benzene and ZnO.

Phenol reacts with dil. HNO₃ at 25°C to give o-Nitrophenol and p-Nitrophenol.

An aqueous solution of phenol reacts with bromine water to give white ppt. of 2,4,6-tribromophenol.

Phenol is sparingly soluble in water at room temperature, while lower alcohols are readily soluble.

Phenol is much more acidic than alcohols due to the resonance stabilization of the phenoxide ion.

Phenol's solution in water has a pH of around 5 or 6, indicating weak acidity.

Phenol is acidic enough to react with strong bases like NaOH to form sodium phenoxide. Alcohols are too weak acids to react with NaOH.

Phenol reacts with bromine water to give a white precipitate of 2,4,6-tribromophenol. Alcohols do not typically react this way.

The Lucas test (using anhydrous ZnCl₂/conc. HCl) differentiates primary, secondary, and tertiary alcohols based on the time taken for turbidity to appear. Tertiary alcohols react immediately, secondary in 5–10 minutes, and primary only on heating.

Both alcohols and phenols react with active metals like sodium to liberate hydrogen gas (e.g., 2ROH + 2Na → 2RONa + H₂).

Ethanol (and other compounds with a CH₃CH(OH)- group or CH₃CO- group) gives a positive iodoform test. Methanol and phenol do not.

Phenols give a characteristic purple or violet color with neutral ferric chloride solution due to the formation of a complex. Alcohols do not give this test.

The -OH group is an activating group, making the benzene ring in phenol much more reactive towards electrophilic aromatic substitution than benzene itself.

Phenol is a weak acid and is generally too weak to affect litmus paper, although it's acidic enough to react with strong bases.

The negative charge on the oxygen of the phenoxide ion (formed after deprotonation of phenol) is delocalized into the benzene ring through resonance, making the phenoxide ion more stable and thus phenol more acidic. Cyclohexanol forms an alkoxide ion which lacks such resonance stabilization.

Methanol is industrially prepared from carbon monoxide and hydrogen (water gas) using ZnO+Cr₂O₃ catalyst.

Denatured alcohol is ethanol made unfit for drinking by adding small amounts of poisonous substances like methanol (methylated spirit), pyridine, or acetone.

Phenol can be prepared industrially from chlorobenzene by Dow's method, which involves reaction with 10% NaOH at high temperature and pressure.

While acidic, phenol is a weak acid and is generally too weak to affect litmus paper.

Phenol reacts with formaldehyde (methanal) in the presence of acid or alkali to yield a polymer called bakelite.

Ethers, like diethyl ether, are generally quite inert towards chemical reagents due to the non-polar nature and stability of the C-O-C bond, making them good solvents.

Ethers have lower boiling points than their isomeric alcohols because they lack the ability to form intermolecular hydrogen bonds among themselves (though they can form H-bonds with water).

Simple or symmetrical ethers have two identical alkyl or aryl groups attached to the oxygen atom (e.g., dimethyl ether, diethyl ether).

According to IUPAC rules, ethers are named as alkoxyalkanes. For CH₃OCH₃, it is methoxymethane.

The solubility of lower alcohols in water is primarily attributed to the formation of hydrogen bonds between the hydroxyl group of the alcohol and water molecules.