1. Draw the structure of Compound A based on its formula and proton NMR. The integration of the peaks from left to right is 5:2:1. Compound A, MF C7H8O
2. Draw the structure of Compound B. Hint: The IR spectrum shows a strong bond at 1725 cm^-1.
3. Draw the structure of Compound C. Hint: The IR spectrum shows no peaks near 1720 cm^-1.
These three problems are emphasizing the use of proton NMR spectra to determine the structure of organic compounds. Lets look at them one by one.
We are told that the molecular formula is C7H8O.
This is valuable information! How many degrees of unsaturation are found in this molecule? You should see that this molecule is highly unsaturated, meaning it probably has many carbon-carbon double bonds, and possibly is cyclic, maybe even has a carbon-oxygen double bond (?). Read further on the subject of "degrees of unsaturation" in any general textbook or search on the Web.
Now examine the NMR spectrum. You should have a book with representative NMR spectra and should be familiar with chemical shifts expected for various types of protons. You should also have a general idea of splitting patterns to be expected and review the spectra of representative simple molecules such as acetone, methyl ethyl keone, toluene etc. You can find these kinds of spectra in books or ...