Organic Chemistry Laboratory I - Chem 341

Quiz 8d

1. Define or give an example to explain the following NMR term: integration curve. (2 pts)

Heterotopic hydrogens are adjacent to each other and are not chemically equivalent. Thus, they are attached to different types of atoms or functional groups. For instance the methyl protons of diethyl ether are attached to a CH2 group, whereas the methylene protons are attached to a methyl group and an oxygen atom. So they will show up at different chemical shifts, in this case the methylene protons are pulled downfield by the oxygen atom. Since the methyl and methylene protons are different chemical shifts, then it will require a different amount of energy to flip the spins into resonance. Therefore heterotopic protons will split each other and the splitting patterns depend on the number of adjacent heterotopic protons.

2. Circle the structure most consistent with the following ¹H NMR spectrum. (2 pts)

3. How many different types of protons are present in the following compound? (2 pts)

Since the molecule is symmetric the left half is the same as the right half. Thus, this compound has four unique types of protons.

4. Consider the compound below and answer the following questions:

(a) What would the splitting pattern for the protons on carbon b look like? (e.g. singlet, doublet, triplet, etc.) (2 pts)

Sextet because it has five adjacent protons, so n = 5 and n+1 = 6.

(b) Specify where the protons on carbon c would show up on the ¹H NMR spectrum, i.e. what ppm? (2 pts)

Proton c is adjacent to the oxygen of an ester, which is an electron withdrawing roup. This would push it downfiled to about 4 ppm. 2 pts for 4 ± 1 ppm. Since c is adjacent to two protons, it will show up as a triplet.