Chapter 1

How many different isomers are there of \(\mathrm{CH}_{2} \mathrm{Br}_{4}\) ? (Assume free-rotating tetrahedral carbon and univalent hydrogen and bromine.) How could one determine which of these isomers is which by the substitution method?

A compound of formula \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{Br}_{2}\) is found to give only a single substance, \(\mathrm{C}_{3} \mathrm{H}_{5} \mathrm{Br}_{3}\), on further substitution. What is the structure of the \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{Br}_{2}\) isomer and of its substitution product?

A compound of formula \(\mathrm{C}_{5} \mathrm{H}_{12}\) gives only a single monobromo substitution product of formula \(\mathrm{C}_{5} \mathrm{H}_{11} \mathrm{Br}\). What is the structure of this \(\mathrm{C}_{5} \mathrm{H}_{12}\) isomer? (Notice that carbon can form both continuous chains and branched chains. Also notice that structures such as the following represent the same isomer because the bonds to carbon are tetrahedral and are free to rotate.)

A gaseous compound of formula \(\mathrm{C}_{2} \mathrm{H}_{4}\) reacts with liquid bromine \(\left(\mathrm{Br}_{2}\right)\) to give a single \(\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{Br}_{2}\) compound. The \(\mathrm{C}_{2} \mathrm{H}_{4} \mathrm{Br}_{2}\) so formed gives only one \(\mathrm{C}_{2} \mathrm{H}_{3} \mathrm{Br}_{3}\) substitution product. Deduce the structure of \(\mathrm{C}_{2} \mathrm{H}_{4}\) and the bromo compounds derived from it. (This was a key problem for the early organic chemists.)

The compound \(\mathrm{C}_{2} \mathrm{H}_{5}\) Br reacts slowly with the compound \(\mathrm{CH}_{4} \mathrm{O}\) to yield a single substance of formula \(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}\). Assuming normal valences throughout, write structural formulas for \(\mathrm{CH}_{4} \mathrm{O}\) and the three different possible structural (not rotational) isomers of \(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}\) and show how the principle of least structural change favors one of them as the reaction product. What would you expect to be formed from each of these three \(\mathrm{C}_{3} \mathrm{H}_{8} \mathrm{O}\) isomers with strong hydrobromic acid?

There are a large number of known isomers of \(\mathrm{C}_{5} \mathrm{H}_{10}\), and some of these are typically unsaturated, like ethene, while others are saturated, like ethane. One of the saturated isomers on bromine substitution gives only one compound of formula \(\mathrm{C}_{5} \mathrm{H}_{9} \mathrm{Br}\). Work out a structure for this isomer of \(\mathrm{C}_{5} \mathrm{H}_{10}\) and its monobromo substitution product.

Lithium hydride could be written as either \(\mathrm{Li}^{\oplus}: \mathrm{H}^{\ominus}\) or \(\mathrm{H}^{\oplus}: \mathrm{Li}^{\ominus}\) depending on whether lithium or hydrogen is more electron-attracting. Explain why hydrogen is actually more electron-attracting, making the correct structure \(\mathrm{Li}^{\oplus}: \mathrm{H}^{\ominus}\).

An acid \((\mathrm{HA})\) can be defined as a substance that donates a proton to a base, for example water. The protondonation reaction usually is an equilibrium reaction and is written as $$ \mathrm{H}: \mathrm{A}+\mathrm{H}: \ddot{\mathrm{O}}: \mathrm{H} \rightleftarrows \mathrm{H}: \stackrel{\mathrm{H}}{\mathrm{O}} \cdot \stackrel{\oplus}{\mathrm{H}}+: \AA^{\ominus} $$ Predict which member of each of the following pairs of compounds would be the stronger acid. Give your reasons. a. \(\mathrm{LiH}, \mathrm{HF}\) b. \(\mathrm{NH}_{3}, \mathrm{H}_{2} \mathrm{O}\) c. \(\mathrm{H}_{2} \mathrm{O}_{2}, \mathrm{H}_{2} \mathrm{O}\) d. \(\mathrm{CH}_{4}, \mathrm{CF}_{3} \mathrm{H}\)

(This problem is in the nature of review of elementary inorganic chemistry and may require reference to a general chemistry book.) Write Lewis structures for each of the following compounds. Use distinct, correctly placed dots for the electrons. Mark all atoms that are not neutral with charges of the proper sign. a. ammonia, \(\mathrm{NH}_{3}\) b. ammonium bromide, \(\mathrm{NH}_{4} \mathrm{Br}\) c. hydrogen cyanide, \(\mathrm{HCN}\) d. ozone \(\left(\angle \mathrm{O}-\mathrm{O}-\mathrm{O}=120^{\circ}\right)\) e. carbon dioxide, \(\mathrm{CO}_{2}\) f. hydrogen peroxide, \(\mathrm{HOOH}\) g. hydroxylamine, \(\mathrm{HONH}_{2}\) h. nitric acid, \(\mathrm{HNO}_{3}\) i. hydrogen sulfide, \(\mathrm{H}_{2} \mathrm{~S}\) j. boron trifluoride, \(\mathrm{BF}_{3}\)

There are two isomers of \(\mathrm{C}_{3} \mathrm{H}_{6}\) with normal carbon and hydrogen valences. Each adds bromine - one rapidly and the other very sluggishly - to give different isomers of \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{Br}_{2}\). The \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{Br}_{2}\) derived from the \(\mathrm{C}_{3} \mathrm{H}_{6}\) isomer that reacts sluggishly with bromine can give just two different \(\mathrm{C}_{3} \mathrm{H}_{5} \mathrm{Br}_{3}\) isomers on further bromine substitution, whereas the other \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{Br}_{2}\) compound can give three different \(\mathrm{C}_{3} \mathrm{H}_{5} \mathrm{Br}_{3}\) isomers on further substitution. What are the structures of the \(\mathrm{C}_{3} \mathrm{H}_{6}\) isomers and their \(\mathrm{C}_{3} \mathrm{H}_{6} \mathrm{Br}_{2}\) addition products?

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.