Question

Question: For each compound give the number of \({}^{\bf{1}}{\bf{H}}\)NMR signals, and then determine how many peaks are present for each NMR signal.

a.

b.

c.

d.

Short answer

a. 2 NMR signals, splitting into quartet and triplet.

b. 4 NMR signals, splitting into two singlets and two triplets.

c. 2 NMR signals, splitting into triplet and quartet.

d. 3 NMR signals, splitting into a triplet, doublet, and singlet.

Step-by-step solution

NMR Spectroscopy

The study of physical, biological, and chemical properties of matter is done using NMR phenomena. The structure and molecular identity can be determined by using NMR spectroscopy.

Medical practitioners use multidimensional NMR imaging techniques and MRI for diagnostic purposes.

Determination of splitting pattern in a molecule

• First, determine the number of different types of protons.
• Nonequivalent protons on the adjacent carbon or the same carbon can split each other.
• Finally, apply the \(\left( {{\rm{n + 1}}} \right)\)rule.

Determination of NMR signals and number of peaks

Representation of protons in a

Since two different kinds of protons are present, the number of NMR signals is 2.

\({{\rm{H}}_{\rm{a}}}\) forms a quartet, as the neighboring C atom has 3 protons. \({{\rm{H}}_{\rm{b}}}\)has a triplet peak as the neighboring c atom has 2 hydrogen atoms in it.

Representation of protons in b

Since four different kinds of protons are present, the number of NMR signals is 4.

\({{\rm{H}}_{\rm{a}}}\) and \({{\rm{H}}_{\rm{d}}}\), both form a singlet, as the neighboring C atom has no proton in it. \({{\rm{H}}_{\rm{b}}}\)and \({{\rm{H}}_{\rm{c}}}\)have a triplet peak as the neighboring c atom has 2 hydrogen atoms in it.

Representation of protons in c

Since two different kinds of protons are present, the number of NMR signals is 2.

\({{\rm{H}}_{\rm{a}}}\) forms a doublet, as the neighboring C atom has a single proton in it. And \({{\rm{H}}_{\rm{b}}}\)has a quartet peak as the neighboring c atom has 3 hydrogen atoms in it.

Representation of protons in d

Since three different kinds of protons are present, the number of NMR signals is 3.

\({{\rm{H}}_{\rm{a}}}\) forms a triplet peak, as the neighboring C atom has two protons. \({{\rm{H}}_{\rm{b}}}\)forms a doublet peak as the neighboring c atom has a single hydrogen atom in it. \({{\rm{H}}_{\rm{c}}}\) forms a singlet, as the neighboring C atom has no proton in it.