91Ó°ÊÓ

Why is the boiling point of water \(\left(100^{\circ}\right)\) substantially higher than the boiling point of methane \(\left(-161^{\circ}\right)\) ?

Dimethylmercury, \(\mathrm{CH}_{3}-\mathrm{Hg}-\mathrm{CH}_{3}\), is a volatile compound of bp \(96^{\circ}\), whereas mercuric fluoride \(\mathrm{F}-\mathrm{Hg}-\mathrm{F}\) is a high-melting solid having mp \(570^{\circ} .\) Explain what differences in bonding in the two substances are expected that can account for the great differences in physical properties.

There are four possible isomers of \(\mathrm{C}_{4} \mathrm{H}_{9} \mathrm{Br}\). Let us call two of these \(A\) and \(B\). Both \(A\) and \(B\) react with water to give the same isomer of \(\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}\) and this isomer of \(\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}\) reacts with strong \(\mathrm{HBr}\) to give back only \(A .\) Substitution of \(A\) with bromine gives only one of the possible \(\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{Br}_{2}\) isomers. Substitution of \(B\) with bromine gives three different \(\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{Br}_{2}\) isomers, and one of these is identical with the \(\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{Br}_{2}\) from the substitution of \(A\). Write structural formulas for \(A\) and \(B\), and the isomers of \(\mathrm{C}_{4} \mathrm{H}_{8} \mathrm{Br}_{2}\) formed from them with bromine, and for the isomers of \(\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}\) expected to be formed from them with water. Indicate in which reaction the principle of least structural change breaks down.