1. What are organic compounds containing halogens?
Answer: Organic compounds containing halogens are compounds in which one or more halogen atoms (fluorine, chlorine, bromine, iodine) are bonded to carbon atoms within an organic molecule.
2. Describe the general methods of preparation for alkyl halides.
Answer: Alkyl halides can be prepared by halogenation of alkanes, hydrohalogenation of alkenes and alkynes, and substitution reactions of alcohols with hydrogen halides (HX).
3. How are aryl halides typically prepared?
Answer: Aryl halides are typically prepared by the direct halogenation of aromatic rings using halogens in the presence of a catalyst like iron (Fe) or iron halides (FeX₃), or by Sandmeyer reactions, where diazonium salts react with halide ions.
4. Explain the nature of the C-X bond in halogenated organic compounds.
Answer: The C-X bond in halogenated organic compounds is polar due to the significant electronegativity difference between carbon and the halogen atom, with the halogen being more electronegative.
5. What are the common physical properties of alkyl halides?
Answer: Alkyl halides typically have higher boiling points than alkanes of similar molecular weight due to the polar C-X bond, are generally insoluble in water, and have varying densities with heavier halogens (bromine and iodine) resulting in denser compounds.
6. What is nucleophilic substitution reaction in the context of alkyl halides?
Answer: Nucleophilic substitution reaction in alkyl halides involves the replacement of the halogen atom (leaving group) by a nucleophile, resulting in the formation of a new compound. This can occur via SN1 or SN2 mechanisms.
7. Differentiate between SN1 and SN2 mechanisms.
Answer: The SN1 mechanism involves a two-step process with the formation of a carbocation intermediate, favored by tertiary alkyl halides, while the SN2 mechanism is a single-step process with a backside attack by the nucleophile, favored by primary alkyl halides.
8. Explain the reactivity order of alkyl halides towards nucleophilic substitution.
Answer: The reactivity order of alkyl halides towards nucleophilic substitution typically follows: RI > RBr > RCl > RF, due to the decreasing bond strength and increasing polarizability of the C-X bond.
9. What are the main uses of chloroform?
Answer: Chloroform is used as a solvent in organic synthesis, in the production of the refrigerant Freon, and historically as an anesthetic.
10. Discuss the environmental effects of chloroform.
Answer: Chloroform is a potential carcinogen and can contribute to ozone depletion. It is toxic to aquatic life and can contaminate groundwater.
11. What is iodoform and how is it used?
Answer: Iodoform (CHI₃) is a yellow solid with antiseptic properties. It is used in medicine for dressing wounds and as a disinfectant.
12. Describe the environmental impact of iodoform.
Answer: Iodoform can be toxic to aquatic organisms and may cause long-term adverse effects in the aquatic environment. It is also a potential pollutant in soil and water.
13. What are freons and where are they used?
Answer: Freons are a class of chlorofluorocarbons (CFCs) used primarily as refrigerants, propellants in aerosol applications, and in the manufacture of foams.
14. Explain the environmental concerns associated with freons.
Answer: Freons contribute significantly to ozone layer depletion, leading to increased UV radiation reaching the Earth’s surface, which can cause skin cancer and other environmental harm.
15. What is DDT and its primary use?
Answer: DDT (Dichlorodiphenyltrichloroethane) is a synthetic insecticide used historically to control mosquito-borne diseases like malaria and in agriculture to protect crops from pests.
16. Discuss the environmental impact of DDT.
Answer: DDT is persistent in the environment, bioaccumulates in the food chain, and can cause adverse effects on wildlife, particularly birds. Its use has been banned or restricted in many countries due to its long-term ecological and health effects.
17. What is the role of halogens in substitution reactions?
Answer: Halogens act as leaving groups in nucleophilic substitution reactions. Their ability to stabilize the negative charge formed during the transition state makes them effective in these reactions.
18. How do the properties of alkyl halides influence their reactions?
Answer: The physical and chemical properties of alkyl halides, such as bond strength, polarity, and steric hindrance, influence their reactivity in nucleophilic substitution and elimination reactions.
19. Describe the mechanism of an elimination reaction involving alkyl halides.
Answer: Elimination reactions, such as E1 and E2 mechanisms, involve the removal of a halogen atom and a hydrogen atom from adjacent carbon atoms, resulting in the formation of an alkene. E1 is a two-step process involving a carbocation intermediate, while E2 is a single-step concerted mechanism.
20. What are some safety precautions when handling halogenated organic compounds?
Answer: Safety precautions include working in well-ventilated areas, using protective gloves and eyewear, avoiding inhalation or skin contact, and proper storage and disposal according to safety guidelines to prevent environmental contamination and health hazards.