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Chapter 14: Q73P (page 527)

The 1 H NMR spectrum of N,N-dimethylformamide shows three singlets at 2.9, 3.0, and 8.0 ppm. Explain why the two\(C{H_3}\)groups are not equivalent to each other, thus giving rise to two NMR signals.

Short Answer

Expert verified

The number of signals in a PMR spectrum is equal to the number of kinds of protons present in the molecule.The splitting of the NMR signal is caused by spin-spin coupling.

Step by step solution

01

Step 1: \(^{\bf{1}}{\bf{H}}\) NMR

The number of signals in a PMR spectrum is equal to the number of kinds of protons present in the molecule.The splitting of the NMR signal is caused by spin-spin coupling.

02

Non-equivalent proton in NMR

The structure for N,N-dimethylformamide places the two\(C{H_3}\)groups in different environments and different chemical shifts. One\(C{H_3}\)group is cis to the O atom, and one is cis to the H atom.

This gives rise to two different absorptions for the\(C{H_3}\)groups.

It should be noted that spin-spin splitting is observed only between non-equivalent neighboring protons.

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Most popular questions from this chapter

Draw the four constitutional isomers having molecular formula \({{\bf{C}}_{\bf{4}}}{{\bf{H}}_{\bf{9}}}{\bf{Br}}\) and indicate how many different kinds of carbon atoms each has.

Draw a splitting diagram for Hb in trans-1,3-dichloropropene, given that Jab = 13.1 Hz and Jbc = 7.2 Hz.

How many 1H NMR signals does each compound show?

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Question: Identify the structures of isomers A and B (molecular formula C9H10O ).

Compound A: IR peak at 1742 cm-1 ; 1 H NMR data (ppm) at 2.15 (singlet, 3 H), 3.70 (singlet, 2 H), and 7.20 cm-1(broad singlet, 5 H). Compound B: IR peak at 1688 ; 1 H NMR data (ppm) at 1.22 (triplet, 3 H), 2.98 (quartet, 2 H), and 7.28–7.95 (multiplet, 5 H).

How many peaks are observed in the 1HNMR signal for each proton shown in red in palau'amine, the complex chapter-opening molecule?
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