The key difference between proton NMR of methyl benzoate and phenylacetic acid is that proton NMR of methyl benzoate does not show any peak after 8.05 ppm whereas phenylacetic acid shows a peak at 11.0 ppm.
The term NMR stands for Nuclear Magnetic Resonance. A proton NMR analysis is the nuclear magnetic resonance that analyses the protons in a molecule. The chemical structures of methyl benzoate and phenylacetic acid are nearly similar; thus, their proton NMR graphs also show similarities. Therefore, it is important to understand the differences between these two NMR graphs.
CONTENTS
1. Overview and Key Difference
2. What is Proton NMR of Methyl Benzoate
3. What is Proton NMR of Phenylacetic Acid
4. Side by Side Comparison – Proton NMR of Methyl Benzoate vs Phenylacetic Acid in Tabular Form
5. Summary
What is Proton NMR of Methyl Benzoate?
The proton NMR of methyl benzoate has its peaks in the range of 3.0 ppm to 8.05 ppm. Methyl benzoate is an aromatic ester. It contains a carbonyl group connected to –O-CH3 group and a benzene ring (phenyl group).
When the proton NMR of methyl benzoate is observed, we can see that there are peaks at 3.89 ppm, 7.56 ppm, 7.66 ppm, and 8.05 ppm. These NMR peaks stand for the following protons in the methyl benzoate molecule.
- Peak at 3.89 stands for the three hydrogen atoms (protons) attached to the methyl group of –O-CH3 group. This is a single peak because the three protons are chemically equivalent. However, the height of the peak is large, to indicate three peaks.
- Peak at 7.56 ppm stands for the protons at the meta position of the benzene ring. These protons are also chemical equivalent.
- Peak at 7.66 ppm stands for the para positioned proton in the benzene ring. This is a less intense peak because it indicates a single proton.
- Peaks at 8.05 ppm stand for the two protons at the ortho position of benzene ring. These two protons are also chemically equivalent.
What is Proton NMR of Phenylacetic Acid?
The proton NMR of phenylacetic acid has its peaks in the range of 3.0 ppm to 11.0 ppm. Phenylacetic acid is a carboxylic acid compound having a benzene ring (phenyl group) attached to the carboxylic group via a –CH2- group.
When the proton NMR for this compound is obtained, we can observe peaks at 3.70 ppm, 7.26 ppm, 7.33 ppm, 7.23 ppm, and at 11.0 ppm. These NMR peaks stand for the following protons in the phenylacetic acid molecule.
- Peak at 3.70 stands for the two protons in the –CH2- group that connects the carbonyl carbon to the phenyl group. This peak height is large because it represents the two chemically equivalent protons in a single NMR signal.
- Peaks at 7.23 ppm stand for two protons at the ortho position of the benzene ring.
- Peak at 7.26 ppm stands for the para positioned proton in the phenyl group.
- Peaks at 7.33 ppm stand for the protons in the meta position of the benzene ring.
- The small peak at 11.0ppm is specific because it represents the hydrogen atom (proton) of the –OH group of the carboxylic acid group.
What is the Difference Between Proton NMR of Methyl Benzoate and Phenylacetic Acid?
The term NMR stands for Nuclear Magnetic Resonance. A proton NMR analyses the protons in a molecule. The key difference between proton NMR of methyl benzoate and phenylacetic acid is that the proton NMR of methyl benzoate does not show any peak after 8.05 ppm whereas phenylacetic acid shows a peak at 11.0 ppm.
Below infographic tabulates the differences between proton NMR of methyl benzoate and phenylacetic acid.
Summary – Proton NMR of Methyl Benzoate vs Phenylacetic Acid
The term NMR stands for Nuclear Magnetic Resonance. A proton NMR analyses the protons in a molecule. The key difference between proton NMR of methyl benzoate and phenylacetic acid is that the proton NMR of methyl benzoate does not show any peak after 8.05 ppm whereas phenylacetic acid shows a peak at 11.0 ppm.
Reference:
1. “Phenylacetic acid.” Molbase, Available here.
Image Courtesy:
1. “Methyl benzoate” By Benrr101 – Own work (Public Domain) via Commons Wikimedia
2. “Kwas fenylooctowy” By Arrowsmaster – Own work (Public Domain) via Commons Wikimedia