1. What are the general methods of preparation for alcohols?
Answer: Alcohols can be prepared by hydration of alkenes, reduction of aldehydes, ketones, carboxylic acids, and esters, and by the hydrolysis of alkyl halides.
2. Describe the properties of alcohols.
Answer: Alcohols are generally polar compounds, with hydrogen bonding leading to higher boiling points compared to other hydrocarbons of similar molecular weight. They are soluble in water to varying degrees depending on the length of the carbon chain.
3. How are phenols different from alcohols in terms of acidity?
Answer: Phenols are more acidic than alcohols due to the stabilization of the phenoxide ion by resonance. The negative charge on the oxygen atom can be delocalized onto the aromatic ring.
4. What is the general structure of ethers?
Answer: Ethers have an oxygen atom connected to two alkyl or aryl groups (R-O-R’). They are relatively non-polar and have lower boiling points compared to alcohols of similar molecular weight.
5. Explain the identification of primary, secondary, and tertiary alcohols.
Answer: Primary alcohols have the hydroxyl group attached to a carbon atom with at least two hydrogen atoms, secondary alcohols have the hydroxyl group attached to a carbon atom with one hydrogen atom, and tertiary alcohols have the hydroxyl group attached to a carbon atom with no hydrogen atoms.
6. Describe the mechanism of dehydration of alcohols.
Answer: The dehydration of alcohols to form alkenes involves the protonation of the hydroxyl group, loss of a water molecule to form a carbocation, and deprotonation to form the alkene. This process is typically catalyzed by acid.
7. What are electrophilic substitution reactions in phenols?
Answer: Electrophilic substitution reactions in phenols include halogenation, nitration, and sulfonation, where the phenolic ring reacts with electrophiles to substitute a hydrogen atom on the ring.
8. Explain the Reimer-Tiemann reaction.
Answer: The Reimer-Tiemann reaction involves the formylation of phenols using chloroform and a strong base to produce ortho-formylated phenols.
9. What is the structure of ethers?
Answer: Ethers have a general structure of R-O-R’, where an oxygen atom is bonded to two alkyl or aryl groups.
10. Describe the nature of the carbonyl group in aldehydes and ketones.
Answer: The carbonyl group (C=O) in aldehydes and ketones is polar, with the oxygen atom being more electronegative than the carbon atom, leading to a partial positive charge on the carbon and a partial negative charge on the oxygen.
11. What are nucleophilic addition reactions to the >C=O group?
Answer: Nucleophilic addition reactions to the carbonyl group involve the addition of a nucleophile to the electrophilic carbon atom of the carbonyl group, forming a tetrahedral intermediate.
12. Compare the relative reactivities of aldehydes and ketones.
Answer: Aldehydes are generally more reactive than ketones towards nucleophilic addition reactions due to less steric hindrance and greater positive charge on the carbonyl carbon.
13. What are some important reactions of aldehydes and ketones?
Answer: Important reactions include nucleophilic addition reactions (e.g., addition of HCN, NH3, and its derivatives), Grignard reactions, oxidation, reduction (Wolf-Kishner and Clemmensen reductions), aldol condensation, Cannizzaro reaction, and Haloform reaction.
14. Explain the Wolf-Kishner reduction.
Answer: The Wolf-Kishner reduction involves the reduction of carbonyl compounds to alkanes using hydrazine and a strong base like potassium hydroxide under high temperatures.
15. What is the Clemmensen reduction?
Answer: The Clemmensen reduction involves the reduction of carbonyl compounds to alkanes using zinc amalgam and hydrochloric acid.
16. Describe the aldol condensation reaction.
Answer: The aldol condensation involves the reaction of an enolate ion with a carbonyl compound to form a β-hydroxy aldehyde or ketone, which can then undergo dehydration to form a conjugated enone.
17. What is the Cannizzaro reaction?
Answer: The Cannizzaro reaction is a redox reaction where two molecules of a non-enolizable aldehyde react in the presence of a strong base to form one molecule of alcohol and one molecule of carboxylic acid.
18. Explain the Haloform reaction.
Answer: The Haloform reaction involves the halogenation of methyl ketones (or alcohols that can form methyl ketones) in the presence of a base to produce a haloform (CHX3) and a carboxylate ion.
19. How can you chemically distinguish between aldehydes and ketones?
Answer: Aldehydes can be distinguished from ketones using Tollen’s reagent (which gives a silver mirror with aldehydes) and Fehling’s solution (which gives a red precipitate with aldehydes).
20. Discuss the acidic strength of carboxylic acids and factors affecting it.
Answer: The acidic strength of carboxylic acids is due to the resonance stabilization of the carboxylate ion. Factors affecting acidic strength include the inductive effect of substituents, resonance effects, and hydrogen bonding. Electronegative substituents and electron-withdrawing groups increase acidity.