Question

Compound A with molecular formula C₆H₁₀ has two peaks in its ¹H NMR spectrum, both of which are singlets (with ratio 9 : 1). Compound Areacts

with an acidic aqueous solution containing mercuric sulfate to form compound B,which gives a positive iodoform test (Problem 58) and has an ¹H NMR

spectrum that shows two singlets (with ratio 3 : 1). Identify A and B.

Short answer

NMR stands for Nuclear Magnetic Resonance Spectroscopy. This is the technique used for determining the structure of organic compounds.

The number of signals present in NMR reflects the number of magnetically different protons. Thus, the number of signal reflects the number of chemically different protons or sets of protons. For example, methanol has two different set of protons (methyl and hydroxyl).

The relative intensities of the signal reflect the relative number of protons of different kind present in the molecule.For example,${\mathbf{CH}}_3{\mathbf{CH}}_2\mathbf{OH}$has three types of protons and three NMR signals. So, relative intensities are 3:2:1

Step-by-step solution

Number of signals and their relative intensities 

NMR stands for Nuclear Magnetic Resonance Spectroscopy. This is the technique used for determining the structure of organic compounds.

The number of signals present in NMR reflects the number of magnetically different protons. Thus, the number of signal reflects the number of chemically different protons or sets of protons. For example, methanol has two different set of protons (methyl and hydroxyl).

The relative intensities of the signal reflect the relative number of protons of different kind present in the molecule.For example,${\mathbf{CH}}_3{\mathbf{CH}}_2\mathbf{OH}$has three types of protons and three NMR signals. So, relative intensities are 3:2:1

Identifying A and B

It is given that compound B shows positive iodoform test. It indicates that Compound B is a methyl ketone. The two singlet with ratio 3:1 indicates the presence of three methyl groups and only one hydrogen in the compound; or if the methyl group represents one, then other nine are hydrogens. The former does not agree with the molecular formula. Thus, the compound must have three identical methyl groups that are attached to a carbon that is not attached to hydrogen.

3,3-dimethylbut-1yne shows two singlets with ratio 9:1. When water is added, it will form 3,3-dimethylbutan-2-one with two singlets with a ratio of 3:1.

2 signal 2 signal

Compound A Compound B