Discuss the nature of $\mathrm{C}-\mathrm{X}$ bond in the haloarenes.
In haloarenes, carbon of benzene is bonded to halogen. Electronegativity of halogen is more than that of $s p^2$ hybridised carbon of benzene ring. So, $\mathrm{C}-\mathrm{X}$ bond is a polar bond. Apart from this, lone pair of electrons of halogen atom are involved in resonance with benzene ring. So, this $\mathrm{C}-\mathrm{X}$ bond has acquire partial bond character.
This $\mathrm{C}-X$ bond of haloarenes is less polar than $\mathrm{C}-X$ bond of haloalkanes. This is supported by the fact that dipole moment of chlorobenzene ( $\mu=1.69 \mathrm{D}$ ) is little lower than that of $\mathrm{CH}_3 \mathrm{Cl}(\mu=1.83 \mathrm{D})$
How can you obtain iodoethane from ethanol when no other iodine containing reagent except NaI is available in the laboratory?
Ethanol is treated with red phosphorous and bromine mixture and the product formed will be bromoethane. The bromoethane so formed is then treated with Nal to give iodoethane.
$$\begin{gathered} \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{OH} \xrightarrow{\mathrm{Red} \mathrm{P} / \mathrm{Br}_2} \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{Br} \\ \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{Br} \xrightarrow{\mathrm{Nal}} \mathrm{CH}_3 \mathrm{CH}_2 \mathrm{I}+\mathrm{NaBr} \end{gathered}$$
This reaction is known as Finkelstein reaction.
Cyanide ion acts as an ambident nucleophile. From which end it acts as a stronger nucleophile in aqueous medium? Give reason for your answer.
Cyanide ion $(\bar{:}C \equiv \mathrm{~N}$ ) is an ambident nucleophile because it can react either through carbon or through nitrogen. Since, $\mathrm{C}-\mathrm{C}$ bond is stronger than $\mathrm{C}-\mathrm{N}$ bond so, cyanide ion will mainly attack through carbon to form alkyl cyanide.
Match the the compounds given in Column I with the effect given in Column II.
| Column I | Column II | ||
|---|---|---|---|
| A. | Chloramphenicol | 1. | Malaria |
| B. | Thyroxine | 2. | Anaesthetic |
| C. | Chloroquine | 3. | Typhoid fever |
| D. | Chloroform | 4. | Goiter |
| 5. | Blood substituent |
A. $\rightarrow(3)$ B. $\rightarrow$ (4) C. $\rightarrow$ (1) D. $\rightarrow(2)$
A. Chloramphenicol is a broadspectrum antibiotic. It is used in the treatment of typhoid fever.
B. Thyroxine is a hormone secreated by thyroid gland. Execessive secretion of thyroxine in the body is known as hyperthyroidism. Most patient with hyper thyroidism have an enlarged thyroid gland i.e., goitre.
C. Chloroquine prevents the development of malaria parasite plasmodium vivax in the blood.
D. IUPAC name of chloroform is trichloromethane with formula $\mathrm{CHCl}_3$. It is a colourless, volatile, sweet-smelling liquid. Its vapours depresses the central nervous system and used as an anaesthetic.
Match the items of Column I and Column II.
| Column I | Column II | ||
|---|---|---|---|
| A. | $\mathrm{S_N 1}$ reaction | 1. | vic-dibromides |
| B. | Chemicals in fire extinguisher | 2. | gem-dihalides |
| C. | Bromination of alkenes | 3. | Racemisation |
| D. | Alkylidene halides | 4. | Saytzeff rule |
| E. | Elimination of HX from alkylhalide | 5. | Chlorobromocarbons |
A. $\rightarrow(3)$ B. $\rightarrow$ (5) C. $\rightarrow$ (1) D. $\rightarrow$ (2) E. $\rightarrow$ (4)
A. A mixture containing two enantiomers in equal proportions will have zero optical rotation, such a mixture is known as racemic mixture. The process of conversion of enantiomer into a racemic mixture is known as racemisation. If an alkyl halide follows $\mathrm{S}_{\mathrm{N}} 1$ mechanism then racemisation takes place while if it follows $\mathrm{S}_{\mathrm{N}} 2$ mechanism than inversion takes places.
B. Chlorobromocarbons are used in fire extinguishers.
C. In vicinal dihalides, halogen atoms are present on the adjacent carbon atom. Bromination of alkenes will give vicinal dihalides.
D. Alkylidene halides are named as gem-dihalides. In gem-dihalides halogen atoms are present on same carbon atom.
E. Elimination of HX from alkylhalide follows Saytzeff rule. This rule states that "in dehydrohalogenation reactions, the preferred product is that alkene which has the greater number of alkyl groups attached to the doubly bonded carbon atoms".