Chapter 14: Q21P (page 527)
Question: How many signals are present in the \({}^{\bf{1}}{\bf{H}}\)NMR spectrum for each molecule? What splitting is observed in each signal?
Short Answer
Step by step solution
Step 1: \({}^{\bf{1}}{\bf{H}}\) NMRSpectroscopy
The number of signals in a proton NMR (\({}^{\bf{1}}{\bf{H}}\)NMR) spectroscopy depends on the number of protons and their chemical environment.
Chemically equivalent protons resonate at the same frequency and exhibit a single signal.
The hydrogen atoms attached to heteroatoms give only a single signal.
Splitting of signals in \({}^{\bf{1}}{\bf{H}}\) NMR spectroscopy
The splitting of the \({}^1H\)NMR signal of a particular proton/hydrogen depends on the number of hydrogens present on the adjacent carbon atoms.
The splitting and multiplicity of a hydrogen atom are predicted using the n+1 rule, where n represents the number of hydrogens present on the carbon atoms adjacent to the hydrogen atom under consideration.
Signals in \({}^{\bf{1}}{\bf{H}}\) NMR spectrum of the given compounds
a. Since the compound consists of three chemically distinct groups, it exhibits three signals.
Non-equivalent protons in compound a
The a, b, and c hydrogen atoms exhibit a singlet each, as, in the case of a and b, there are no hydrogen atoms on the carbon adjacent to it. In c, the hydrogen is attached to a heteroatom.
b. The given compound exhibits four NMR signals.
Non-equivalent protons in compound b
The multiplicity of a is \(2 + 1\; = 3\) (triplet).
The multiplicity of b is \(5 + 1\; = 6\) (multiplet)
The multiplicity of c is \(2 + 1\; = 3\) (triplet).
The multiplicity of d is a singlet.
c. The given compound exhibits three NMR signals.
Non-equivalent protons in compound c
The multiplicity of a is \(1 + 1\; = 2\) (doublet).
The multiplicity of b is \(6 + 1\; = 7\) (multiplet)
The multiplicity of c is a singlet.
Over 30 million students worldwide already upgrade their learning with Vaia!
