Chapter 24

Primary amides give a strong peak at \(m / e 44\) in their mass spectra. Indicate the nature of this peak and suggest how it might be formed.

a. Draw the two important valence-bond structures for a nitrilium ion \([\mathrm{RCNR}]^{\oplus}\) and write the steps involved in hydration of a nitrilium ion to an amide, RCONHR. b. Would you expect \(\mathrm{N}\) -methylethanamide to be formed from methanol and ethanenitrile in \(\mathrm{H}_{2} \mathrm{SO}_{4}\) ? Explain.

Nitriles are converted readily to amides with hydrogen peroxide in dilute sodium hydroxide solution. The reaction is $$ \mathrm{RC} \equiv \mathrm{N}+2 \mathrm{H}_{2} \mathrm{O}_{2} \stackrel{\mathrm{OH}^{\ominus}}{\longrightarrow} \mathrm{RCONH}_{2}+\mathrm{O}_{2}+\mathrm{H}_{2} \mathrm{O} $$ The rate equation is $$ v=k\left[\mathrm{H}_{2} \mathrm{O}_{2}\right][\stackrel{\ominus}{\mathrm{O}} \mathrm{H}][\mathrm{R} \mathrm{C} \equiv \mathrm{N}] $$

Nitriles of the type \(\mathrm{RCH}_{2} \mathrm{CN}\) undergo a self-addition reaction analogous to the aldol addition in the presence of strong bases such as lithium amide. Hydrolysis of the initial reaction product with dilute acid yields a cyanoketone, \(\mathrm{RCH}_{2} \mathrm{COCH}(\mathrm{CN}) \mathrm{R}\). Show the steps that are involved in the mechanism of the overall reaction and outline a scheme for its use to synthesize large-ring ketones of the type \(\left(\mathrm{CH}_{2}\right)_{n} \mathrm{C}=\mathrm{O}\) from dinitriles of the type \(\mathrm{NC}\left(\mathrm{CH}_{2}\right)_{n} \mathrm{CN}\).

Show how the following substances can be synthesized from the indicated starting materials: a. \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCN}\) from \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCl}\) (two ways) b. \(\mathrm{CH}_{3} \mathrm{CH}=\mathrm{CHCN}\) from \(\mathrm{CH}_{2}=\mathrm{CHCH}_{2} \mathrm{Br}\) c. \(\mathrm{CH}_{2}=\mathrm{CHCO}_{2} \mathrm{H}\) from \(\mathrm{CH}_{3} \mathrm{CHO}\)

Tetracyanoethene in benzene forms an orange solution, but when this solution is mixed with a solution of anthracene in benzene, a brilliant blue-green color is produced, which fades rapidly; colorless crystals of a compound of composition \(\mathrm{C}_{14} \mathrm{H}_{10} \cdot \mathrm{C}_{2}(\mathrm{CN})_{4}\) then are depositied. Explain the color changes that occur and write a structure for the crystalline product.

Would you expect the dipole moment measured for \(1,3,5\) -trinitrobenzene in 1,3,5-trimethylbenzene solution to be the same as in tetrachloromethane solution? Explain.

Anthracene (mp \(217^{\circ}\) ) forms a red crystalline complex (mp \(164^{\circ}\) ) with 1,3,5-trinitrobenzene (mp \(121^{\circ}\) ). If you were to purify anthracene as this complex, how could you regenerate the anthracene free of trinitrobenzene?

Write the mechanistic steps to show how 1,2 -diphenyldiazene oxide and 1,2 -diphenyldiazene may be formed by base-induced condensation reactions of nitrosobenzene with N-phenylazanol and benzenamine, respectively. What product would you expect to be formed from nitrosobenzene and \(\mathrm{N}\) -(4-chlorophenyl)azanol? Give your reasoning.

What kind of properties and reactions would you expect the double bond of nitroethene to have? Consider the ease of electrophilic and nucleophilic addition reactions as well as cycloadditions.

Devise a synthesis (more than one step may be required) of 2 from 2 -propanone, hydrazine, and hydrogen cyanide. What would you expect this substance to yield when heated in (a) a perfluorohydrocarbon solvent and (b) a solution of bromine in carbon tetrachloride?

Explain why 1,2-diazacyclopropene reacts with acids much more slowly than does diazomethane.

Suggest a route for the synthesis of each of the following compounds from the indicated starting material: a. 2 -methylpropanenitrile from 2 -methylpropanal b. \(\left(\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{CH}_{2}\right)_{3} \mathrm{C}-\mathrm{NO}_{2}\) from nitromethane c. N-tert-butylbenzenecarboxamide from benzenecarbonitrile (benzeonitrile)

How would you synthesize the following compounds from the indicated starting materials? Write equations for the reactions involved and indicate the reaction conditions. a. phenylnitroethanoic acid from ethyl phenylethanoate b. 3-phenylpropanoic acid from phenylethanoic acid

For each of the following pairs of compounds give a chemical test, preferably a test-tube reaction, that will distinguish the two compounds. Write a structural formula for each compound and equations for the reactions involved. a. 1 -methyl-3-nitrobenzene and phenylnitromethane b. 1 -methyl-4-nitrobenzene and benzenecarboxamide c. benzenamine and cyclohexanamine d. N-methylbenzenamine and 4-methylbenzenamine e. N-nitroso-N-methylbenzenamine and 4-nitroso-N-methylbenzenamine