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Introduction

Note-06/30/13-This page isunder construction and is not eligible for bonus points.

Spectroscopy and spectrometry are powerful tools in an organic chemist's toolbox. The compounds that today's organic chemists investigate generally have large, complex structures. Delineation of those structures requires piecing together molecular fragments that are revealed by NMR, IR and MS data. The solutions to the following puzzles require the integration of information obtained from 13C-NMR, 1H-NMR, IR, and MS data. Correlation charts for each technique are available in the chapters dealing with C-NMR, H-NMR, IR and MS.

Puzzle 1

Elemental analysis of an unknown compound reveals that it contains 72.06% C and 12.10% H. The mass spectrum, 13C-NMR, 1H-NMR, IR, and spectra are shown in Figures 1-4, respectively.

Figure 1

Mass Spectrum of an Unknown Compound


Exercise 1 What is the m/z value of the molecular ion for this compound?

Exercise 2 What is the maximum number of carbon atoms possible in this structure?

Exercise 3 What molecular fragment does the parent peak at m/z = 15 suggest? Hint-Think α-cleavage.

Exercise 4 What molecular fragment does the parent peak at m/z = 43 suggest? Hint-Think α-cleavage.

Exercise 5 The peak at m/z = 58 results from the loss of a fragment that has an m/z value of

Exercise 6 Draw the structure that is consistent with your answer to Exercise 5. Hint-Think McLafferty rearrangement.


Figure 2

13C-NMR Spectrum of an Unknown Compound

Exercise 7 How many unique carbon atoms are there in this compound?

Exercise 8 The peak at 209 ppm suggests the presence of a group in this compound. (The IR data will confirm this.)


Figure 3

1H-NMR Spectrum of an Unknown Compound


Exercise 9 The peak at 0.88 ppm integrates for  H.

This suggests two  groups.

The signal from 2.04-2.17 ppm integrates for H.

This is consistent with a group

and a group.

The peak at 2.29 ppm integrates for H.

This is consistent with a group.

The splitting pattern indicates that this group is bonded to a group.

The peak at 0.88 ppm is a .

This means that there is hydrogen atom on the adjacent carbon.

Taken together, these two pieces of the puzzle indicate that the compound contains the molecular fragment .


Figure 4

IR Spectrum of an Unknown Compound


Exercise 10 The strong peak at 1720 cm-1 suggests that the compound contains a .

Exercise 11 Draw a structure that is consistent with the information from all of these spectra.


Puzzle 2

Elemental analysis of an unknown compound reveals that it contains 82.41% C and 6.92% H. The mass spectrum, 13C-NMR, 1H-NMR, IR, and spectra are shown in Figures 5-8, respectively.

Figure 5

Mass Spectrum of an Unknown Compound

Exercise 12 What is the m/z value of the molecular ion for this compound?

Exercise 13 Draw the structure of the ion that is suggested by the peak at m/z = 91.

Figure 6

13C-NMR Spectrum of an Unknown Compound

Exercise 14 How many unique carbon atoms are there in this compound?

Exercise 15 How many aromatic carbons are there in this compound?

Exercise 16 What functional group has a carbon that resonates at roughly 120 ppm?

Figure 7

1H-NMR Spectrum of an Unknown Compound

Exercise 17 The peak at 2.62 ppm integrates for  H.

Exercise 18 The peak at 2.96 ppm integrates for  H.

Exercise 19 The peaks at 2.62 and 2.96 are both  .

Exercise 20 This spin-spin splitting pattern indicates that this compound contains the molecular fragment  .

Exercise 21 The peaks in the range 7.2-7.4 integrate for H.

Exercise 22 How many substituents are attached to the aromatic ring? .

Exercise 23 Integration of all the peaks in the spectrum indicates that the compound contains H atoms.

Figure 8

IR Spectrum of an Unknown Compound

Exercise 24 Does the IR spectrum indicate the presence of a carbonyl group?

Exercise 25 What functional group(s) is(are) consistent with the strong peak at 2247 cm-1?

Exercise 26 Draw the structure of a compound that is consistent with all the spectral data.

Puzzle 3

Try this one on your own. Elemental analysis of an unknown compound reveals that it contains 47.19% C and 3.96% H. The mass spectrum, 13C-NMR, 1H-NMR, IR, and spectra are shown in Figures 9-12, respectively.

Figure 9

Mass Spectrum of an Unknown Compound

Figure 10

13C-NMR Spectrum of an Unknown Compound

Figure 11

1H-NMR Spectrum of an Unknown Compound

Figure 12

IR Spectrum of an Unknown Compound

Exercise 27 Draw the structure of a compound that is consistent with all the spectral data.