Problem 43
Explain why 2-chloropyridine reacts with potassium amide \(\left(\mathrm{KNH}_{2}\right)\) in liquid ammonia solution at \(-33^{\circ}\) to give 2 -aminopyridine, whereas 3 -chloropyridine under the same conditions gives a mixture of \(65 \% 4\) -amino- and \(35 \%\) 3aminopyridine.
Problem 45
Explain why the substitution reactions of the following halonaphthalenes give about the same ratio of 1 - and 2- naphthyl products independently of the halogen substituent and the nucleophilic reagent. Show the steps involved.
Problem 50
Nucleophilic displacement of the halogen of 3,5-dimethyl-4-nitrobromobenzene is much slower than with the corresponding compound lacking the methyl groups. Give a reasonable explanation of this observation. (Construction of molecular models will help.)
Problem 51
Methylmagnesium halides have been employed as analytical reagents for the determination of the number of acidic hydrogens in a molecule (the Zerewitinoff determination). The method involves measuring the amount of methane produced from a given weight of compound (such as \(\mathrm{RH}\), with an acidic hydrogen) by the following reaction: $$ \mathrm{CH}_{3} \mathrm{MgI}+\mathrm{RH} \rightarrow \mathrm{CH}_{4}+\mathrm{RMgI} $$ Excess methylmagnesium iodide and \(0.1776 \mathrm{~g}\) of Compound A (formula \(\mathrm{C}_{4} \mathrm{H}_{10} \mathrm{O}_{3}\) ) react to give \(84.1 \mathrm{~mL}\) of methane collected over mercury at \(740 \mathrm{~mm}\) and \(25^{\circ}\). How many acidic hydrogens does Compound A possess per molecule? Suggest a possible structure on the basis that spectral data indicate (a) there is no \(\mathrm{C}=\mathrm{O}\) group in the molecule and (b) \(\mathbf{A}\) is achiral.
Problem 52
From the nature of the carbon-metal bonds in organometallic compounds, predict the products of the following reactions. Give your reasoning. a. \(\mathrm{CH}_{3} \mathrm{MgCl}+\mathrm{ICl}\) b. \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{Li}+\mathrm{CH}_{3} \mathrm{OH}\) c. \(\mathrm{CH}_{3} \mathrm{Li}+\mathrm{HC} \equiv \mathrm{CH}\) d. \(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{Li}+\mathrm{CuI}\)
Problem 54
The following experimental observations have been reported: 1\. tert-Butyl chloride was added to lithium metal in dry ether at \(35^{\circ}\). A vigorous reaction ensued with evolution of hydrocarbon gases. After all the lithium metal was consumed, the mixture was poured onto dry ice. The only acidic product that could be isolated (small yield) was 4,4-dimethylpentanoic acid. 2\. tert-Butyl chloride was added to lithium metal in dry ether at \(-40^{\circ}\). After all the lithium had reacted, the mixture was carbonated and gave a good yield of 2,2-dimethylpropanoic acid. 3\. tert-Butyl chloride was added to lithium metal in dry ether at \(-40^{\circ} .\) After all the lithium was consumed, ethene was bubbled through the mixture at \(-40^{\circ}\) until no further reaction occurred. Carbonation of this mixture gave a good yield of 4,4-dimethylpentanoic acid. a. Give a reasonably detailed analysis of the results obtained and show as best you can the mechanisms involved in each reaction. b. Would similar behavior be expected with methyl chloride? Explain. c. Would you expect that a substantial amount of 6,6-dimethylheptanoic acid would be found in Observation 3? Explain.
Problem 55
Predict the products of each of the following Grignard reactions before and after hydrolysis. Give reasoning or analogies for each. a. \(\mathrm{CH}_{3} \mathrm{MgI}+\mathrm{HCO}_{2} \mathrm{C}_{2} \mathrm{H}_{5} \rightarrow\) b. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}(\mathrm{MgBr}) \mathrm{CH}_{3}+2,4\) -dimethyl-3-pentanone \(\rightarrow\) c. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{MgBr}+\mathrm{CS}_{2} \rightarrow\) d. \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{MgBr}+\mathrm{NH}_{3} \rightarrow\)
Problem 58
Each of the following equations represents a "possible" but not actually feasible Grignard synthesis. Consider each equation and determine why it will not proceed satisfactorily as written. Give your reasoning and show what the actual product will be. a. \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CMgBr}+\left[\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}\right]_{2} \mathrm{C}=\mathrm{O} \rightarrow \rightarrow\left(\mathrm{CH}_{3}\right)_{3} \mathrm{C}\left[\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CH}\right]_{2} \mathrm{COH}\) b. \(\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCH}_{2} \mathrm{MgBr}+\left[\left(\mathrm{CH}_{3}\right)_{3} \mathrm{C}\right]_{2} \mathrm{C}=\mathrm{O} \rightarrow \rightarrow\left(\mathrm{CH}_{3}\right)_{3} \mathrm{CCH}_{2}\left[\left(\mathrm{CH}_{3}\right)_{3} \mathrm{C}\right]_{2} \mathrm{COH}\) ?. \(\mathrm{CH}_{3} \mathrm{MgI}+\mathrm{CH}_{3}\left(\mathrm{CH}_{3}\right)_{2} \mathrm{COCl} \rightarrow \rightarrow \mathrm{CH}_{3}\left(\mathrm{CH}_{3}\right)_{2} \mathrm{COCH}_{3}\) d. \(\mathrm{CH}_{3} \mathrm{MgI}+\mathrm{CH}_{3} \mathrm{CCH}=\mathrm{N}-\mathrm{CH}_{3} \rightarrow \rightarrow \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{~N}\left(\mathrm{CH}_{3}\right)_{2}\) e. \(\mathrm{BrCH}_{2} \mathrm{CH}_{2} \mathrm{O}_{2} \mathrm{CCH}_{3} \underset{\left(\mathrm{CH}_{2} \mathrm{H}_{5}\right)_{2} \mathrm{O}}{\stackrel{\mathrm{Mg}}{\longrightarrow}}\) Grignard reagent \(\stackrel{\mathrm{CH}_{2} \mathrm{O}}{\longrightarrow} \rightarrow \mathrm{HOCH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{O}_{2} \mathrm{CCH}_{3}\) f. \(\mathrm{CH}_{2}=\mathrm{CHCH}_{2} \mathrm{MgCl}+\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{Br} \rightarrow \mathrm{CH}_{2}=\mathrm{CH}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CH}_{3}\)
Problem 61
The rate of addition of dimethylmagnesium to excess diphenylmethanone (benzophenone) in diethyl ether initially is cleanly second order, that is, first order in ketone and first order in \(\left(\mathrm{CH}_{3}\right)_{2} \mathrm{Mg}\). As the reaction proceeds, the rate no longer follows a strictly second-order rate overall. Suggest how the apparent specific rate could change as the reaction proceeds.
Problem 65
Compound X, of formula \(\mathrm{C}_{3} \mathrm{H}_{5} \mathrm{Br}_{3}\), with methyllithium formed bromocyclopropane and 3-bromopropene. The NMR spectrum of \(\mathrm{X}\) showed a one-proton triplet at \(5.9 \mathrm{ppm}\), a two-proton triplet at \(3.55 \mathrm{ppm}\), and a complex resonance centered at \(2.5\) ppm downfield from TMS. What is the structure of \(X\) ? Account for the products observed in its reaction with methyllithium.
