Q5. Give the main product when propene is treated with (i) water and dilute acid, (ii) diborane and then H2O2 in aqueous NaOH.
(i) Propan-2-ol, CH3CH(OH)CH3 (Markovnikov addition). (ii) Propan-1-ol, CH3CH2CH2OH: boron goes to the end carbon, so the –OH ends up there, as if water had added against Markovnikov’s rule (NCERT pages 199–200).
Q6. Arrange phenol, m-nitrophenol, p-cresol and o-nitrophenol in order of increasing acid strength, using NCERT Table 7.3.
Increasing acid strength means decreasing pKa: p-cresol (10.2) < phenol (10.0) < m-nitrophenol (8.3) < o-nitrophenol (7.2) (NCERT page 207).
Q7. What volume of hydrogen, at 273.15 K and 1 bar, is given off when 4.6 g of sodium reacts completely with excess ethanol? (Na = 23 g mol−1; molar volume 22.7 L mol−1.)
2C2H5OH + 2Na → 2C2H5ONa + H2. 4.6/23 = 0.20 mol Na gives 0.10 mol H2: 0.10 × 22.7 = 2.27 L (reasoned from NCERT page 205).
Q8. Which alkene is the main product when butan-2-ol is dehydrated with acid, and which alcohol, butan-2-ol or 2-methylpropan-2-ol, dehydrates more easily?
But-2-ene, the more substituted alkene (reasoned from Saytzeff’s rule, which NCERT Unit 6, page 180, states for dehydrohalogenation). 2-Methylpropan-2-ol, a tertiary alcohol, dehydrates more easily: the order is 3° > 2° > 1°, because its carbocation is the most stable (NCERT page 209).
Q9. Phenol is heated with zinc dust. Name the product and state why this is unusual for an –OH compound.
Benzene: C6H5OH + Zn → C6H6 + ZnO. It is the one reaction in which phenol’s C–O bond breaks; with other reagents only alcohols break the C–O bond (NCERT pages 208 and 213).