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 are not shown in the link below but would be an intense singlet at 9.4 ppm.
The answer is b
The reason why we only see four peaks in the 1H NMR spectrum of heptanedioic acid is because the molecule is symmetrical. The peaks we observe in the spectrum correspond to different types of hydrogen atoms in the molecule. Since heptanedioic acid is symmetrical, the five CH2 groups are equivalent to each other, resulting in only one peak for all the CH2 groups. Similarly, the two OH groups are also equivalent to each other, giving us another peak.
So, the correct answer is b. Heptanedioic acid is a symmetrical molecule.