Why do we only see four peaks in the 1H NMR when we have five CH2 groups and 2 OH groups?
Answer
a. There should be more peaks, but they peaks are overlapping in the spectrum.
b. Heptanedioic acid is a symmetrical molecule.
c. Heptanedioic acid is a chiral molecule.
d. Heptanedioic acid is an unsymmetrical molecule.
molecule is heptanedioic acid also known as pimelic acid.
HNMR
triplet at 2.3 ppm, quintet at 1.55, quintet at 1.25
the hydoxyl hydrogens would be an intense singlet at 9.4 ppm.
I would say C. Heptanedioic acid is a chiral molecule.
Please let me know if its right.
The answer is b
The correct answer to why we only see four peaks in the 1H NMR of heptanedioic acid is option b. Heptanedioic acid is a symmetrical molecule.
To understand this, we need to analyze the structure of heptanedioic acid. Heptanedioic acid has five CH2 groups and two OH groups.
In the 1H NMR spectrum, each different hydrogen environment in a molecule will produce a peak. The number of peaks corresponds to the number of unique hydrogen environments in the molecule.
In heptanedioic acid, since it is a symmetrical molecule, the five CH2 groups are equivalent and have the same hydrogen environment. Hence, they will produce a single peak in the 1H NMR spectrum.
Additionally, the two OH groups in heptanedioic acid are also equivalent, producing another single peak in the spectrum.
Therefore, we see a total of four peaks: one for the CH2 groups (which will appear as a multiplet due to the neighboring protons) and one for the OH groups (which will appear as a singlet due to there being no neighboring protons).