Problem 65
3-Methylbutan-2-ol has five signals in its \({ }^{13} \mathrm{C}\) NMR spectrum at 17.90 , \(18.15,20.00,35.05,\) and \(72.75 \delta .\) Why are the two methyl groups attached to \(\mathrm{C} 3\) nonequivalent? Making a molecular model should be helpful.
Problem 66
A 13 C NMR spectrum of commercially available pentane-2,4-diol shows five peaks at \(23.3,23.9,46.5,64.8,\) and \(68.1 \delta .\) Explain.
Problem 67
Carboxylic acids \(\left(\mathrm{RCO}_{2} \mathrm{H}\right)\) react with alcohols \(\left(\mathrm{R}^{\prime} \mathrm{OH}\right)\) in the presence of an acid catalyst. The reaction product of propanoic acid with methanol has the following spectroscopic properties. Propose a structure. $$ \mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COH} \quad \frac{\mathrm{O}}{\mathrm{H}^{+} \text {catalyst }} \quad ? $$ Propanoic acid \(\mathrm{MS}: \mathrm{M}^{+}=88\) \(\mathrm{IR}: 1735 \mathrm{~cm}^{-1}\) 1H NMR: \(1.11 \delta(3 \mathrm{H},\) triplet, \(J=7 \mathrm{~Hz}) ; 2.32 \delta(2 \mathrm{H},\) quartet, \(J=7 \mathrm{~Hz})\) \(3.65 \delta(3 \mathrm{H},\) singlet \()\) \({ }^{13} \mathrm{C} \mathrm{NMR}: 9.3,27.6,51.4,174.6 \delta\)
Problem 68
Nitriles (RC\equivN) react with Grignard reagents (R'MgBr). The reaction product from 2 -methylpropanenitrile with methylmagnesium bromide has the following spectroscopic properties. Propose a structure. $$ \mathrm{CH}_{3} \mathrm{CHC} \equiv \mathrm{N} \quad \frac{1 . \mathrm{CH}_{3} \mathrm{MgBr}}{2 \mathrm{H}_{3} \mathrm{O}^{+}} \quad ? $$ 2-Methylpropanenitrile \(\mathrm{MS}: \mathrm{M}^{+}=86\) \(\mathrm{IR}: 1715 \mathrm{~cm}^{-1}\) \({ }^{1} \mathrm{H}\) NMR: \(1.05 \delta(6 \mathrm{H},\) doublet, \(J=7 \mathrm{~Hz}) ; 2.12 \delta(3 \mathrm{H},\) singlet \() ; 2.67 \delta\) \((1 \mathrm{H},\) septet \(, J=7 \mathrm{~Hz})\) \({ }^{13} \mathrm{C} \mathrm{NMR}: 18.2,27.2,41.6 .211 .2 \delta\)
