Haloalkanes and Haloarenes, on the exam screen.

Propan-1-ol reacting with $\mathrm{PCl}_{5}$ gives 1-chloropropane together with phosphoryl chloride ($\mathrm{POCl}_{3}$) and HCl, so X = $\mathrm{POCl}_{3}$. Alcoholic KOH dehydrohalogenates 1-chloropropane to propene (Y). Addition of HBr in the presence of a peroxide follows the anti-Markovnikov (peroxide/Kharasch) effect, placing Br on the terminal carbon to give 1-bromopropane, so Z = $\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CH}_{2}\mathrm{Br}$. Hence X = $\mathrm{POCl}_{3}$, Z = $\mathrm{CH}_{3}\mathrm{CH}_{2}\mathrm{CH}_{2}\mathrm{Br}$.

Why the other options are wrong:

- (1) Wrong: peroxide effect gives 1-bromopropane, not isopropyl bromide.
- (3) Wrong: $\mathrm{PCl}_{5}$ gives $\mathrm{POCl}_{3}$ (not $\mathrm{H}_{3}\mathrm{PO}_{3}$) and Z is the primary bromide.
- (4) Wrong: $\mathrm{PCl}_{5}$ gives $\mathrm{POCl}_{3}$, not $\mathrm{H}_{3}\mathrm{PO}_{3}$ ($\mathrm{H}_{3}\mathrm{PO}_{3}$ comes from $\mathrm{PCl}_{3}$).

The reactants are cyclohexylmagnesium bromide and cyclohexylamine. A Grignard reagent is a very strong base and is destroyed by an acidic N-H proton: $\mathrm{C}_{6}\mathrm{H}_{11}-\mathrm{MgBr} + \mathrm{C}_{6}\mathrm{H}_{11}-\mathrm{NH}_{2} \rightarrow \mathrm{C}_{6}\mathrm{H}_{12} + \mathrm{C}_{6}\mathrm{H}_{11}-\mathrm{NH}-\mathrm{MgBr}$. The organic product derived from the Grignard reagent is therefore cyclohexane, option (4); no new C-C or C-N bond is formed. NCERT Class 12, Haloalkanes and Haloarenes (Grignard reagents).

Why the other options are wrong:

- (1) assumes the Grignard carbon substitutes at nitrogen; proton transfer occurs instead
- (2) assumes C-C coupling while retaining the amino group, but there is no electrophilic carbon or coupling catalyst
- (3) assumes direct coupling of the two cyclohexyl groups rather than acid-base proton transfer

The elimination reaction of 2-Bromo-pentane to form pent-2-ene is a $\beta$-elimination reaction, follows Zaitsev's rule, and is a dehydrohalogenation reaction. Dehydration involves removing a water molecule, which is not the case here. Chapter: Haloalkanes and Haloarenes.