91Ó°ÊÓ

Question: What molecular ions would you expect for compounds having each of the following molecular formulas: (a)${\mathbf{C}}_4{\mathbf{H}}_9\mathbf{Cl}$; (b)${\mathbf{C}}_3{\mathbf{H}}_7\mathbf{F}$; (c)${\mathbf{\text{C}}}_{\mathbf{\text{4}}}{\mathbf{\text{H}}}_{\mathbf{\text{11}}}\mathbf{\text{N}}$; (d)${\mathbf{\text{C}}}_{\mathbf{\text{4}}}{\mathbf{\text{H}}}_{\mathbf{\text{4}}}{\mathbf{\text{N}}}_{\mathbf{\text{2}}}$?

Question:Like alcohols, ethers undergo α cleavage by breaking a carbon–carbon bond between an alkyl group and the carbon bonded to the ether oxygen atom; that is, the red C–C bond in $\mathbf{R}–{\mathbf{CH}}_2\mathbf{OR}\text{'}$is broken. With this in mind, propose structures for the fragments formed by α cleavage of${\left({\mathbf{CH}}_3\right)}_2{\mathbf{CHCH}}_2{\mathbf{OCH}}_2{\mathbf{CH}}_3$. Suggest a reason why an ether fragments by α cleavage.

Question: What major IR absorptions are present above 1500 ${\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$for each compound?

Question: How would each of the following pairs of compounds differ in their IR spectra?

Question:Reduction of cyclohex-2-enone can yield cyclohexanone, cyclohex-2-enol, or cyclohexanol, depending on the reagent and reaction conditions. How could you use IR spectroscopy to distinguish the three possible products?

Question: Tell how IR spectroscopy could be used to determine when each reaction is complete.

Question: Match each compound to its IR spectrum.

Question: Propose possible structure consistent with each set of data. Assume each compound has ${\mathbf{sp}}^{\mathbf{3}}$hybridized C-H absorption in its IR spectrum, and that other major IR absorption above 1500${\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$are list.

1. A compound having a molecular ion at 72 and an absorption in its IR spectrum at 1725 ${\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$.
2. A compound having a molecular ion at 55 and an absorption in its IR spectrum at 2250 ${\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$.
3. A compound having a molecular ion at 74 and an absorption in its IR spectrum at 3600-3200 ${\mathbf{cm}}^{\mathbf{-}\mathbf{1}}$.

Question: A chiral hydrocarbon X exhibits a molecular ion at 82 in its massspectrum. The IR spectrum of X shows peaks at 3300, 3000–2850, and 2250 cm^-1. Propose a structure for X.

Question: Treatment of benzaldehyde (${\mathbf{C}}_{\mathbf{6}}{\mathbf{H}}_{\mathbf{5}}\mathbf{CHO}$) with Zn(Hg) in aqueous HCl forms a compound Z that has a molecular ion at 92 in its mass spectrum. Z shows absorptions at 3150–2950, 1605, and 1496 cm^-1 in its IR spectrum. Give a possible structure for Z.