1. What are hydrocarbons?
Answer: Hydrocarbons are organic compounds consisting entirely of hydrogen and carbon atoms. They are the primary components of fossil fuels and are classified into alkanes, alkenes, alkynes, and aromatic hydrocarbons.
2. How are hydrocarbons classified?
Answer: Hydrocarbons are classified into alkanes (saturated hydrocarbons), alkenes (unsaturated hydrocarbons with one or more double bonds), alkynes (unsaturated hydrocarbons with one or more triple bonds), and aromatic hydrocarbons (containing one or more aromatic rings).
3. What is isomerism in hydrocarbons?
Answer: Isomerism in hydrocarbons is the phenomenon where compounds have the same molecular formula but different structural formulas. Types of isomerism include structural isomerism (chain, position, functional group) and stereoisomerism (geometric and optical).
4. What is the IUPAC nomenclature for hydrocarbons?
Answer: The IUPAC nomenclature for hydrocarbons involves naming the longest continuous carbon chain as the parent hydrocarbon and identifying and numbering the substituents based on their position on the chain. Prefixes, infixes, and suffixes are used to indicate the type and position of substituents and functional groups.
5. What are the general methods of preparation for alkanes?
Answer: General methods of preparation for alkanes include hydrogenation of alkenes, Wurtz reaction (coupling of alkyl halides), reduction of alkyl halides, and decarboxylation of carboxylic acids.
6. Describe the conformations of alkanes using Sawhorse and Newman projections.
Answer: Sawhorse projections depict molecules at an angle, showing the spatial arrangement of atoms, while Newman projections show the molecule as viewed along a carbon-carbon bond axis. For ethane, staggered and eclipsed conformations are the most common, with staggered being more stable due to less torsional strain.
7. Explain the halogenation of alkanes and its mechanism.
Answer: Halogenation of alkanes involves the substitution of a hydrogen atom by a halogen atom, typically via a free radical mechanism. The process includes initiation (formation of radicals), propagation (radical chain reactions), and termination (combination of radicals).
8. What is geometrical isomerism in alkenes?
Answer: Geometrical isomerism in alkenes occurs due to restricted rotation around the double bond, leading to different spatial arrangements of substituents. The isomers are classified as cis (same side) and trans (opposite side).
9. Describe the mechanism of electrophilic addition to alkenes.
Answer: Electrophilic addition to alkenes involves the attack of an electrophile on the electron-rich double bond, forming a carbocation intermediate. The intermediate then reacts with a nucleophile to form the addition product.
10. Explain Markownikoff’s rule and its application in the addition of hydrogen halides to alkenes.
Answer: Markownikoff’s rule states that in the addition of hydrogen halides to asymmetrical alkenes, the hydrogen atom attaches to the carbon with more hydrogen atoms (less substituted), and the halide attaches to the carbon with fewer hydrogen atoms (more substituted).
11. What is peroxide effect or anti-Markownikoff’s addition?
Answer: The peroxide effect, or anti-Markownikoff’s addition, occurs in the presence of peroxides where the addition of hydrogen bromide to alkenes follows a different mechanism, leading to the halide attaching to the less substituted carbon atom.
12. What is polymerization and its significance?
Answer: Polymerization is the process of linking monomer units into long chains or networks, forming polymers. It is significant in producing various materials like plastics, rubbers, and synthetic fibers with wide-ranging applications.
13. Discuss the acidic character of alkynes.
Answer: Alkynes exhibit acidic character due to the sp-hybridized carbon atoms, which have a higher s-character and thus, hold the bonded hydrogen more tightly, making it more acidic compared to alkanes and alkenes.
14. Describe the addition reactions of alkynes.
Answer: Alkynes undergo addition reactions with hydrogen, halogens, water, and hydrogen halides. These reactions typically proceed through the formation of a vinyl intermediate, followed by further addition to form the final product.
15. What is the nomenclature of aromatic hydrocarbons?
Answer: The nomenclature of aromatic hydrocarbons follows IUPAC rules, with benzene as the parent compound. Substituents are named and numbered to give the lowest possible numbers, with prefixes like ortho, meta, and para indicating relative positions.
16. Explain the structure and aromaticity of benzene.
Answer: Benzene has a hexagonal ring structure with alternating double bonds (resonance structure), providing equal bond lengths and electron delocalization. Aromaticity refers to the stability conferred by this delocalization, satisfying Hückel’s rule (4n + 2 π electrons).
17. Describe the mechanism of electrophilic aromatic substitution.
Answer: Electrophilic aromatic substitution involves the attack of an electrophile on the aromatic ring, forming a carbocation intermediate (arenium ion). This is followed by deprotonation to restore aromaticity, resulting in the substitution product.
18. What are the halogenation and nitration reactions of benzene?
Answer: Halogenation of benzene involves the substitution of a hydrogen atom by a halogen (chlorine or bromine) using a Lewis acid catalyst. Nitration involves the substitution of a hydrogen atom by a nitro group (NO₂) using a mixture of concentrated nitric and sulfuric acids.
19. Explain Friedel-Crafts alkylation and acylation.
Answer: Friedel-Crafts alkylation involves the substitution of a hydrogen atom with an alkyl group using an alkyl halide and a Lewis acid catalyst. Acylation involves the substitution with an acyl group using an acyl chloride and a Lewis acid catalyst.
20. Discuss the directive influence of functional groups in monosubstituted benzene.
Answer: Functional groups in monosubstituted benzene can be either activating or deactivating and can direct incoming electrophiles to ortho/para or meta positions, respectively. Activating groups (e.g., -OH, -NH₂) direct to ortho/para positions, while deactivating groups (e.g., -NO₂, -CF₃) direct to the meta position.