91Ó°ÊÓ

In addition to the four isomers shown in Section \(28.1,\) draw the structures of three more isomers of \(\mathrm{C}_{6} \mathrm{H}_{13} \mathrm{Cl}\). Name these isomers.

Draw the structures of the following compounds and classify them as primary, secondary or tertiary halogenoalkanes: (a) \(1-\) chloro- 2 -methylhexane (b) 2 -iodobutane (c) 2 -chloro- \(2,3-\) dimethylpentane; (d) 1 -bromo-3-methylbutane.

The boiling points of \(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{X}\) are \(184 \mathrm{K}\) for \(\mathrm{X}=\mathrm{H}, 235 \mathrm{K}\) for \(\mathrm{X}=\mathrm{F}, 285 \mathrm{K}\) for \(\mathrm{X}=\mathrm{Cl}, 311 \mathrm{K}\) for \(X=B r\) and \(345 K\) for \(X=I .\) Comment on the trend in values and the factors that contribute to it.

Outline the mechanism of an \(\mathrm{S}_{\mathrm{N}} 1\) reaction using as your example the reaction between water and 2-chloro-2-methylbutane. Include a rate equation in your answer.

(a) If the reaction of hydroxide ion with optically pure \((S)-3\) -iodo-3-methylheptane leads to a racemate, what can you deduce about the mechanism of the reaction? (b) Write a rate equation for the reaction.

Construct an MO diagram that describes the \(\pi\) -bonding in the allyl cation and show that the bonding is delocalized.

What will be the order of the rates of reactions of water with \(\mathrm{Me}_{3} \mathrm{CBr}, \mathrm{Me}_{2} \mathrm{CHBr}, \mathrm{MeCH}_{2} \mathrm{Br}\) and \(\mathrm{CH}_{3} \mathrm{Br}\) ? Rationalize the order that you propose.

Categorize (giving reasons) the following solvents as (a) non-polar, (b) polar and protic, or (c) polar and aprotic: hexane, acetone, ethanol, DMSO, acetonitrile, water, acetic acid, dichloromethane.

In the \(\mathrm{S}_{\mathrm{N}} 2\) reaction of \(\mathrm{CH}_{3} \mathrm{Br}\) with various nucleophiles, the rate of substitution depends on the nucleophiles in the order \(\mathrm{HS}^{-}>\mathrm{I}^{-}>\mathrm{HO}^{-}>\mathrm{Cl}^{-}>\mathrm{NH}_{3}>\mathrm{H}_{2} \mathrm{O}\) Comment on these data. Suggest where \(F^{-}\) might come in this series.

Discuss the role of the leaving group on the rates of \(\mathrm{S}_{\mathrm{N}} 1\) and \(\mathrm{S}_{\mathrm{N}} 2\) reactions.