3
$\begingroup$

I count 7 equivalent absorptions total, but answer says 8. I don't see where this eighth absorption comes from?

Heres how I'm counting starting on right side of molecule:

1 is Carbox acid H

2 is the 1 H just left of the double bonded Oxygen

3 is the 3 H's of the methyl group next to the lone H

4 and 5 are the 2 sets of equivalent H's in the ring structure

6 is is the 2 H's to left of ring

7 is the 2 methlys on the isoproplyl (these are equivalent so same signal)

How do they get 8?

C13H12O2

Improve this question
$\endgroup$
6
  • 3
    $\begingroup$ 8 is the H on the central carbon of the isopropyl group $\endgroup$
    – ron
    Commented Mar 18, 2016 at 22:31
  • $\begingroup$ thanks for the reply ron. ..I actually already accounted for the H at that location. The isoproply has 2 absorptions: the 2 equivalent methls + the H you just mentioned. So it still sums to 7 $\endgroup$
    – trav95
    Commented Mar 18, 2016 at 22:35
  • 4
    $\begingroup$ No you didn't... $\endgroup$
    – Mithoron
    Commented Mar 18, 2016 at 22:37
  • 2
    $\begingroup$ oh wait.. ..you are 100% correct.. I totally looked over that.. Shouldve noticd the only 3 bonds there hence an H.. $\endgroup$
    – trav95
    Commented Mar 18, 2016 at 22:37
  • 2
    $\begingroup$ It's actually ibuprofen. And technically it's an isobutyl group not isopropyl. $\endgroup$
    – orthocresol
    Commented Mar 19, 2016 at 4:53

2 Answers 2

Reset to default
3
$\begingroup$

To answer this question properly one must understand that the field of the instrument is important. At 400 MHz, ibuprofen displays 7 distinct carbon-bound proton signals. Below is the spectrum from the SDBS website. Although the two methyls of the isobutyl chain are recorded [G] as a "singlet" at δ 0.889, they are diastereotopic and inherently different no matter how far they are removed from the asymmetry on the other side of the ring. If this spectrum were recorded on a 1,020 MHz 1H NMR, perhaps separation of the two methyl signals would occur. That the two methyls are different, imagine that one of them is a perdeutero methyl group. This compound is a diastereomer of the compound having the other methyl group as the perdeutero group. So there are actually 9 total distinct types of hydrogens (including the carboxyl hydrogen) that, given the right spectrometer, could appear in a spectrum of ibuprofen. It is a matter of resolution. [As a case in point, see the 1H NMR of cholesterol at the SDBS website and note that the two methyl groups at the end of the side chain have different chemical shifts even though the are separated from the nearest center of asymmetry by three methylene groups.]

Acknowledgment: http://sdbs.db.aist.go.jp/sdbs/cgi-bin/direct_frame_top.cgi

enter image description here

Improve this answer
$\endgroup$
-1
$\begingroup$

There are 8 non-equivalent protons as shown. Find 8 non-equivalent protons

Improve this answer
$\endgroup$
2
  • $\begingroup$ adianadiadi how did you number the protons? i mean what software? I was trying to do this in chemdoodle but no success. i was totally missing #6 proton for some reason, but ths is pretty clear now thanks $\endgroup$
    – trav95
    Commented Mar 19, 2016 at 16:07
  • $\begingroup$ Numbering done manually. $\endgroup$
    – adianadiadi
    Commented Mar 20, 2016 at 6:35

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.