### Example 4

C7H14O2

MW 130

First calculate the degree of unsaturation: the result is 1. The compound will have a ring or a double bond.

### IR Spectrum

Since the degree of unsaturation indicates that the compound could have a carbonyl, let's look for that first, since carbonyl bands are strong and distinct. Carbonyls show up in the region 1760-1665, and specifically, saturated aliphatic esters from 1750-1735. Sure enough, there is a band at 1740 indicating a saturated aliphatic ester. There is a possibility that the compound is has both a ketone and an ether group instead of an ester, however, the band at 1740 indicates an ester instead of a saturated aliphatic ketone. You can also see bands in the region 1300-1000 which can indicate the C-O stretch.

### Think of possible structures

We think that the compound is an ester, having the functional group -O-(C=O)-. Let's look at the NMR to get an idea of how many different hydrogens are in the molecule so that we can narrow down the number of possible structures.

### Proton NMR Spectrum

The NMR indicates that there are 4 different types of protons in the molecule. The 6 protons at 0.9-1.0 ppm indicate two methyl (-CH3) groups, each adjacent to a carbon which has 2 hydrogens:

These two methyl groups (red, above), situated next to a methylene group (-CH2-), are not very close to an oxygen.

The peak at 4.0-4.1 ppm has two protons, so it is a methylene group. In an ester, hydrogens on a carbon adjacent to the oxygen are from 3.7-4.1 ppm. This leads to the sub-structure below:

The peak at 2.2-2.4 ppm has two protons, so it is a methylene group. In an ester, hydrogens on a carbon adjacent to the carbonyl are from 2.0-2.2 ppm. This leads to the sub-structure below:

Let's line up the substructures we have so far:

If we join the sub-structures as indicated, we have accounted for all 7 carbons. The un-colored protons above must be the 4 hydrogens in the sextet from 1.6-1.8 ppm. This makes sense, since these hydrogens are adjacent to both a carbon with 3 hydrogens and a carbon with 2 hydrogens. Here is the proposed structure with these 4 hydrogens shown in purple:

This is how the structure correlates with the NMR:

### Summary

Example 4 is propyl butanoate:

Note: the nomenclature of esters is discussed briefly in the section on esters.