Organic Chemistry Laboratory I - Chem 341

Quiz 8b

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

Variations in the NMR frequencies of the same kind of nucleus (H¹) are due to variations in the electron density around that nucleus; these are called the chemical shifts. Chemical shifts depend on the electronegativity of the nearby atoms and the hybridization of adjacent atoms.

In a H¹ NMR the chemical shifts of protons usually vary from 0 to 12 ppm.

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 three 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 c look like? (e.g. singlet, doublet, triplet, etc.) (2 pts)

Doublet because it has one adjacent protons, so n = 1 and n+1 = 2.

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

Proton a is aliphatic and is not attached to an electron withdrawing group, so it will show up from about 1 ppm. 2 pts for 1 ± 0.5 ppm. Since a is adjacent to 2 protons, it will be split into a triplet.