Haloalkanes And Haloarenes

Step 1: Identify the -hydrogens and possible alkenes.
Dehydrohalogenation can occur at C2 and C4.
Elimination at C2 gives 3-methylhex-2-ene: (can exist as cis and trans isomers).
Elimination at C4 gives 3-methylhex-3-ene: (can exist as cis and trans isomers).
Step 2: Count the distinct alkenes including stereoisomers.
1. cis-3-methylhex-2-ene
2. trans-3-methylhex-2-ene
3. cis-3-methylhex-3-ene
4. trans-3-methylhex-3-ene
There are 4 distinct alkenes. Thus, the number of distinct alkenes is .

The reactivity of haloarenes towards nucleophilic substitution increases with the number of electron-withdrawing nitro groups.
- For 1-chloro-4-nitrobenzene, higher temperature and NaOH/H\textsuperscript{+} are required.
- 1-chloro-2,4-dinitrobenzene reacts at a slightly lower temperature.
- 1-chloro-2,4,6-trinitrobenzene is highly reactive and can be converted to phenol with just warm water.

S\textsubscript{N}2 reactions are favored in less hindered, primary alkyl halides.
- Compound iii is primary and least hindered.
- Compound i is also primary but slightly more hindered.
- Compound ii is secondary and most hindered.
Hence, the reactivity order is: iii > i > ii.

- The boiling points of haloalkanes depend on their molecular size and structure.
- 1-Chlorobutane (ii) has the highest boiling point because it is a straight-chain molecule and has more surface area for intermolecular forces.
- 2-Chlorobutane (iii) has a lower boiling point than 1-chlorobutane because it is a branched structure, which results in weaker intermolecular forces.
- 2-chloro-2-methylpropane (i) has the lowest boiling point due to its compact, branched structure, which results in the weakest intermolecular forces.
Thus, the correct answer is (2) ii>iii>i.

SN reactions proceed faster when steric hindrance is minimal, as the nucleophile attacks the electrophilic carbon directly. Let’s evaluate steric hindrance around the carbon attached to Br in each compound: \begin{itemize} \item III: (C H ) C(CH )Br – A tertiary benzylic halide; highly hindered slowest. \item II: (C H ) CHBr – Secondary benzylic halide; still hindered. \item I: C H CH(CH )Br – Secondary benzylic halide; less hindered than II. \item IV: C H CH Br – Primary benzylic halide; least hindered fastest. \end{itemize} Hence, SN reactivity order: III< II< I< IV.