13 questions about NMR.

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NMR Tutorial

Adapted from work by Chris P. Schaller; copyright 2008, used by permission.

Explain why, in the following cases, the chemical shift is slightly different from the normal range described.

a) chlorofom (CHCl3): H on sp3 carbon; normally 0-5 but here at 7.27 ppm.

b) vinyl ether (CH2=CHOCH=CH2): H on sp2 carbon normally 5-7 but here at 4.5 ppm.

c) nitrobenzene (C6H5NO2): H on sp2, aromatic carbon normally 7-8 but here 8.5 ppm.

Suggest possible assignments for peaks found at the following positions in the 1H NMR spectrum.

a) 7.4 ppm b) 12.1 ppm

c) 3.6 ppm d) 10.1 ppm

e) 8.2 ppm f) 2.1 ppm

g) 5.8 ppm

Suggest the approximate chemical shift for the circled protons in the following partial structures.

a)

b)

c)

d)

e)

f)

g)

h)

The following are portions of 1H NMR spectra. Each shows the splitting pattern of the hydrogen atoms on a single carbon. The splitting is due to the neighboring hydrogens. Sketch the partial structure showing the arrangement of neighboring hydrogens for each case.

A quartet

A doublet of doublets

A triplet

A doublet of triplets

A heptet

A doublet of doublets of triplets

The following structures contain circled protons. Sketch the number of lines in the proper ratio for the portion of the 1H NMR due to these protons.

Assign the relative number of protons at each position based on the integral lines shown.

  • (Five different peaks)

Suggest partial structures for the following data, given in string form.

  • 8.05 ppm (doublet, 2H)
  • 3.25 ppm (septet, 1H)
  • 6.55 ppm (broad singlet, 1H)
  • 0.94 ppm (triplet, 3H)
  • 2.33 ppm (broad singlet, 2H)
  • 8.65 ppm (singlet, 1H)
  • 2.05 ppm (quartet, 2H)
  • 6.21 ppm (doublet of doublets, 1H)

Sketch the expected 1H spectrum for each of the following structures. (Just show 1 peak for the aromatic protons.)

Draw what the NMR spectrum of ethylbenzene, CH3CH2C6H5, would look like if it was contaminated with an equal amount of tert-butyl methyl ether, (CH3)3COCH3.

10. Draw structures for compounds that have the following 1H NMR spectra features.

a) C3H7Cl; one doublet and one septet

b) C4H8O2; one singlet, one triplet, one quartet

11. Without considering spin-spin splitting, how many 1H and 13C NMR peaks should the following compounds have?

12. What is the structure of C3H6O with the following spectroscopic data? IR: among many peaks, there is one strong peak at 1715 cm1. 1H NMR: only one singlet at 2.1 ppm.

13. What is the structure of C4H7O2Cl (IR: 1740 cm-1) with the following 1H NMR spectrum?