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63

  Substance Equivalent protons Relative intensities
A) HCC-CH3 a) HC 1
b) -CH3 3
B) Substance B a) CH3-CH< 3
b) >CH- 1
c) -CH2- 2
d) -CH3 3
C) H2C=C=CHBr a)H2C= 2
b) =CHBr 1
D) (CH3)2CHOCH(CH3)2 a) 2 * (CH3)2C< 6 (12)
b) 2 * >CH-O 1 (2)
E) Substance E a) 3 * -CH3 3 (9)
b) 3 * Phenyl-H 1 (3)
Did you get everything right? Great!
If you made mistakes in identifying groups of equivalent protons, you might want to re-read the unit on page 8.

Now apply what you have learned about the shape of 1H-NMR spectra to solve the next problem:

Two molecules of ketene CH2=C=O react spontaneously to form the dimeric diketene C4H4O2.
There are two signals in the 1H-NMR spectrum 2 of diketene. The ratio of their relative intensities is 1:1.
Considering this, which of the following four structures is the correct one for the diketene? Once you have come up with a good reason for your choice, click on the image of the correct isomer to see whether you were right!

A)

Isomer A

B)

Isomer B

C)

Isomer C

D)

Isomer D

Would you like to get a hint?