From the ¹³C NMR data, we have deduced the presence of an aldehyde or ketone in the unknown structure and this agrees with the one degree of unsaturation previously calculated. We can further eliminate the aldehyde as a possibility based on the data given. Which piece of data supports this conclusion?
a. The aldehyde proton is not observed in the ¹H NMR at around 12 ppm.
b. The aldehyde proton is not observed in the ¹H NMR at around 7 ppm.
c. The aldehyde proton is not observed in the ¹H NMR at around 9.5 ppm.