(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

Rahul set-up an experiment to find resistance of aqueous $$\mathrm{KCl}$$ solution for different concentrations at $$298 \mathrm{~K}$$ using a conductivity cell connected to a Wheatstone bridge. He fed the Wheatstone bridge with a.c. power in the audio frequency range 550 to 5000 cycles per second. Once the resistance was calculated from null point he also calculated the conductivity $$K$$ and molar conductivity $$\wedge_m$$ and recorded his readings in tabular form.

Answer the following questions:

(a) Why does conductivity decrease with dilution?

(b) If $$\wedge_{\mathrm{m}}{ }^0$$ of $$\mathrm{KCl}$$ is $$150.0 \mathrm{~S} \mathrm{~cm} \mathrm{~mol}^{-1}$$, calculate the degree of dissociation of $$0.01 \mathrm{M} \mathrm{KCl}$$.

(c) If Rahul had used $$\mathrm{HCl}$$ instead to $$\mathrm{KCl}$$ then would you except the $$\wedge_{\mathrm{m}}$$ values to be more or less than those per $$\mathrm{KCl}$$ for a given concentration. Justify.

OR

(c) Amit, a classmate of Rahul repeated the same experiment with $$\mathrm{CH}_3 \mathrm{COOH}$$ solution instead of $$\mathrm{KCl}$$ solution. Give one point that would be similar and one that would be different in his observations as compared to Rahul.

(a) (i) Why is boiling point of $$1 \mathrm{~M} \mathrm{~NaCl}$$ solution more than that of $$1 \mathrm{M}$$ glucose solution?

(ii) A nonvolatile solute '$$\mathrm{X}$$' (molar mass $$=\mathbf{5 0} \mathrm{~g} \mathrm{~mol}^{-1}$$) when dissolved in $$78 \mathrm{~g}$$ of benzene reduced its vapour pressure to $$90 \%$$.

Calculate the mass of $$\mathrm{X}$$ dissolved in the solution.

(iii) Calculate the boiling point elevation for a solution prepared by adding $$10 \mathrm{~g}$$ of $$\mathrm{MgCl}_2$$ to $$200 \mathrm{~g}$$ of water assuming $$\mathrm{MgCl}_2$$ is completely dissociated.

($$\mathrm{K}_{\mathrm{b}}$$ for Water $$=0.512 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$$, Molar mass $$\mathrm{MgCl}_2=95 \mathrm{~g} \mathrm{~mol}^{-1}$$)

OR

(b) (i) Why is the value of Van't Hoff factor for ethanoic acid in benzene close to 0.5 ?

(ii) Determine the osmotic pressure of a solution prepared by dissolving $$2.32 \times 10^{-2} \mathrm{~g}$$ of $$\mathrm{K}_2 \mathrm{SO}_4$$ in $$2 \mathrm{~L}$$ of solution at $$25^{\circ} \mathrm{C}$$, assuming that $$\mathrm{K}_2 \mathrm{SO}_4$$ is completely dissociated.

($$\mathrm{R}=0.082 \mathrm{~L} \mathrm{~atm} \mathrm{~K}^{-1} \mathrm{~mol}^{-1}$$, Molar mass $$\mathrm{K}_2 \mathrm{SO}_4 =174 \mathrm{~g} \mathrm{~mol}^{-1}$$)

(iii) When $$25.6 \mathrm{~g}$$ of sulphur was dissolved in $$1000 \mathrm{~g}$$ of benzene, the freezing point lowered by $$0.512 \mathrm{~K}$$. Calculate the formula of sulphur ($$\mathrm{S}_{\mathrm{x}}$$). ($$\mathrm{K}_{\mathrm{f}}$$ for benzene $$=5.12 \mathrm{~K} \mathrm{~kg} \mathrm{~mol}^{-1}$$, Atomic mass of Sulphur $$=32 \mathrm{~g} \mathrm{~mol}^{-1}$$ )