BR CBT 6 BS 103

[lexw]

The H NMR peak at 7.37 ppm in Figure 1 can BEST be described as a:
a. doublet of doublets with a peak area ratio that is equal to 1 : 2 : 2 : 1
b. doublet of doublets with a peak area ratio that is equal to 1 : 1 : 1 : 1
c. quartet with a peak area ratio of 1 : 3 : 3 : 1
d. quartet with a peak area ratio of 1 : 2 : 2 : 1


Answer A is the best answer. The peak is not a quartet, because the baseline drops to zero in the middle, and the symmetry is not even throughout (i.e., the peaks are not evenly spaced). This eliminates choices C and D. The ratio of the peaks is not 1 : 1 : 1 : 1, so choice B can be eliminated. Perhaps it is not a perfect 1 : 2 : 2 : 1 ratio, but choice A is the best answer. The best answer is A

I'm a little confused as to why its not considered a quartet.

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[ipmed]

Looks like a quartet to me, Doublet-Doublet should have 4 of the same amplitude signals ?

 

[dyspareunia]

Compare a quartet to a doublet of doublets.

 

[lexw]

thanks for the pictures, yeah reading through TBR it showed us that a doublet of doublets indicated a benzene ring. so we're all in agreement this should be a quartet?

 

[charistivity]

bump

Can someone please explain why this is not a 1:1:1:1? The benzene is para-substituted so there are only 4 Ph-H bonds and the integration of 4H supports that. I'm really worried about this. Thanks in advance!

 

[Hadi7183]

Because the diagram clearly shows two central peaks that are twice as high as two lateral peaks. Remember what you see in the 1:2:2:1 ratio is the relative ratio and not the absolute ratio. A 1:2:2:1 ratio still supports the 4H integration - 2/3:4/3:4/3:2/3, which add up to 4H.

 

[charistivity]

That makes sense Hadi!! Thank you so much!