(a) Illustrate Sandmeyer's reaction with an equation.

(b) Explain, why $$\left(\mathrm{CH}_3\right)_2 \mathrm{NH}$$ is more basic than $$\left(\mathrm{CH}_3\right)_3 \mathrm{~N}$$ in aqueous solution.

Give reasons for any 3 of the following observations:

(a) Penta-acetate of glucose does not react with hydroxylamine.

(b) Amino acids behave like salts.

(c) Water soluble vitamins must be taken regularly in diet.

(d) The two strands in DNA are complimentary to each other.

(a) (i) Why is the $$\mathrm{C}-\mathrm{O}$$ bond length in phenols less than that in methanol?

(ii) Arrange the following in order of increasing boiling point:

Ethoxyethane, Butanal, Butanol, n-butane

(iii) How can phenol be prepared from anisole? Give reaction.

OR

(b) (i) Give mechanism of the following reaction:

$$\mathrm{CH}_3-\mathrm{CH}_2-\mathrm{OH} \xrightarrow[413 \mathrm{~K}]{\mathrm{H}_2 \mathrm{SO}_4} \mathrm{CH}_3 \mathrm{CH}_2-\mathrm{O} -\mathrm{CH}_2 \mathrm{CH}_3+\mathrm{H}_2 \mathrm{O}$$

(ii) Illustrate hydroboration - oxidation reaction with an example.

Read the passage carefully and answer the questions that follow :

Nucleophilic Substitution Nucleophilic Substitution reaction of haloalkane can be conducted according to both $$\mathrm{S}_{\mathrm{N}} 1$$ and $$\mathrm{S}_{\mathrm{N}} 2$$ mechanisms. $$S_N 1$$ is a two step reaction while $$S_N 2$$ is a single step reaction. For any haloalkane which mechanism is followed depends on factors such as structure of haloalkane, properties of leaving group, nucleophilic reagent and solvent.

Influences of solvent polarity: In $$\mathrm{S}_{\mathrm{N}} 1$$ reaction, the polarity of the system increases from the reactant to the transition state, because a polar solvent has a greater effect on the transition state than the reactant, thereby reducing activation energy and accelerating the reaction. In $$\mathrm{S}_{\mathrm{N}} 2$$ reaction, the polarity of the system generally does not change from the reactant to the transition state and only charge dispersion occurs. At this time, polar solvent has a great stabilizing effect on $$\mathrm{Nu}$$ than the transition state, thereby increasing activation energy and slow down the reaction rate. For example, the decomposition rate $$\left(\mathrm{S}_{\mathrm{N}} 1\right)$$ of tertiary chlorobutane at $$25^{\circ} \mathrm{C}$$ in water (dielectric constant 79) is 300000 times faster than in ethanol (dielectric constant 24 ). The reaction rate $$\left(\mathrm{S}_{\mathrm{N}} 2\right)$$ of 2 -Bromopropane and $$\mathrm{NaOH}$$ in ethanol containing $$40 \%$$ water is twice slower than in absolute ethanol. Hence the level of solvent polarity has influence on both $$\mathrm{S}_{\mathrm{N}} 1$$ and $$\mathrm{S}_{\mathrm{N}} 2$$ reaction, but with different results. Generally speaking weak polar solvent is favourable for $$\mathrm{S}_{\mathrm{N}} 2$$ reaction, while strong polar solvent is favourable for $$\mathrm{S}_{\mathrm{N}} 1$$. Generally speaking the substitution reaction of tertiary haloalkane is based on $$S_N 1$$ mechanism in solvents with a strong polarity (for example ethanol containing water).

Answer the following questions :

(a) Why racemisation occurs in $$S_N 1$$ ?

(b) Why is ethanol less polar than water?

(c) Which one of the following in each pair is more reactive towards $$S_N 2$$ reaction?

(i) $$\mathrm{CH}_3-\mathrm{CH}_2-\mathrm{I} \text { or } \mathrm{CH}_3 \mathrm{CH}_2-\mathrm{Cl}$$

(ii)

OR

(c) Arrange the following in the increasing order of their reactivity towards $$S_N 1$$ reactions:

(i) 2-Bromo-2-methylbutane, 1-Bromopentane, 2-Bromopentane

(ii) 1-Bromo-3-methylbutane, 2-Bromo-2methylbutane, 2-Bromo-3-methylbutane