Propose structures for ketones or aldehydes that have the following ¹H NMR spectra:

(a) C₉H₁₀O₂

IR: 1695 cm^-1

(b) C₄H₆O

IR: 1690 cm^-1

As the IR peak is observed at 1730 cm^-so the compound must contain the aldehyde functional group or a derivate of an aldehyde group.

As per the NMR graph, the peak at the 6.98 and 7.81 are due to the aromatic ring which is a compound containing the aromatic ring and the peak at 4.08 shows quartet that is methylene group is present with a methyl group and the 1.44 is showing a triplet by the methyl hydrogen due to the 2H of the methylene group so the structure must be:

As the IR peak is observed at 1690 cm^-so the compound must be contain the ketone functional group or a derivate of an carbonyl group.

The peak observed at 9.57 is due to the proton of the carbonyl and the molecular formula is given we can find the unsaturation and the unsaturation is 1 as:

That is one double bond is present in the molecule.

The longest peak at 1.86 is due to the methylene and the peak at 6.0 and 6.31 are due to the proton of the alkene so, the compound must be: