[GoGoGadget]

A couple of weeks ago in my O Chem lab, we had to synthesize Chalcone and then for the second part of it, we had to hydrogenate it and need to determine the product that was produced. We submitted IR and NMR samples for both products and recieved mass spectrums of both as well. There were four potential places on the Chalcone where hydrogenation could have taken place, one at the alkene, one where the ketone is at, one where Cl is at, and one where the methoxy substituent is. From looking at the mass spectrums from both, I believe that the Cl atom was lost and a H atom was replaced in the second reaction. The molecular mass for Chalcone is around 274 and from looking at the mass spectrum for the second product, the molecular peak was around 238, subtracting the mass of Cl. I had a hard time trying to identify the peaks from the NMR spectra and was wondering if somebody could look at what I had so far and how else to determining the remaining peaks. Also for the Chalcone NMR, my prof had said to look for potential peaks in its ketol intermediate but after drawing it out and looking up where peaks are normally found for it, I could only find one corresponding peak for it. The ketol intermediate is what I have drawn out beneath the Chalcone structure in the first NMR spectrum. aOtherwise, I believe I figured out everything for both IR peaks and if somebody could confirm that I have correctly identified the peaks for those spectrums too, I'd appreciate it!

Edit: The top NMR and IR spectrums are those of Chalcone and the bottom NMR and IR spectrums are those of my hydrogenated product.

[Dan]

The molecular mass for Chalcone is around 274 and from looking at the mass spectrum for the second product, the molecular peak was around 238, subtracting the mass of Cl. 

274-238 = 36

Replacing ³⁵Cl with H would be a mass change of 34

An interesting discrepancy of 2 wouldn't you say....

In your second spectrum, we can instantly see 7 aliphatic and 7 aromatic H.

[GoGoGadget]

It is an interesting discrepancy...I just wasn't sure what else to take into account for it. The IR did not indicate the formation of an OH as a peak was not shown for it and it looked the alkene group outside of the aromatic structures was still present so was not sure what else to look at.

[Dan]

You've already said it:

There were four potential places on the Chalcone where hydrogenation could have taken place, one at the alkene, one where the ketone is at, one where Cl is at, and one where the methoxy substituent is.

You are not limited to just one option...

Hydrogenation is addition of hydrogen (H₂). What is the molecular weight of hydrogen?

By the way, cleavage of a bond with hydrogen, for example:

Ph-Cl + H₂ ---> Ph-H + H-Cl

is a hydrogenolysis, not a hydrogenation.

alkene group outside of the aromatic structures was still present

Aromatic/alkene region is typically 7-8 ppm. The peaks around 3 are most definitely aliphatic.

[GoGoGadget]

OH! Ok thanks a ton! That helps a lot! That would mean the double bond that formed was hydrogenated then. And thanks for clarifying on what happened with the Cl, that makes sense! I'll go back and look at my NMR spectrums then, thanks again!

[GoGoGadget]

I guess for right now, are my peaks labled correctly for the NMR spectrum of Chalcone? And I could not for the life of me figure out the other peaks that were present.

[Dan]

I think the peaks you have assigned are probably correct, but you have only identified 3 out of 6 signals. The structure drawn on the spectrum labelled "chalcone 1" is not correct though - the OMe should be at the para position.

[GoGoGadget]

Thanks for looking at what I have so far! Would the rest of the peaks correspond to the ketol intermediate of the chalcone? My professor had given my class some characteristic peaks with chemical shifts to look at but my data did not seem to correspond to hers. One peak from the ketol was to look for a doublet at around 3.3 but I ended up with a singlet at 3.8.

[Dan]

No, it looks like the clean chalcone product. You will see 7 signals for it (I said 6 before, but I forgot the methyl group).

[GoGoGadget]

Thanks for looking it over! I went back and reanalyzed it and think I was wrong about some of the peaks before and redid it.

Also on the IR, I saw the the carbonyl group shifted to a higher energy level from the Chalcone product to that of the hydrogenated product. Would this happen due to resonance from the double bond on chalcone to forming an anionic charge onto the O atom? I'm not for sure on how to accurately explain that.

Otherwise do my NMR's look correct?

[GoGoGadget]

If anyone could look this over, it'd be really appreciated. I wanted to see if I was on the right track with my spectrums.

[GoGoGadget]

I talked with my TA in lab the other day and he only mentioned he typically figures out the peaks of NMR spectra by measuring the integration values of each peak and then going from there to match the peaks up to the hydrogen groups. If I'm not correct, would someone be able to explain how to determine peaks from their integration values? 

[discodermolide]

I talked with my TA in lab the other day and he only mentioned he typically figures out the peaks of NMR spectra by measuring the integration values of each peak and then going from there to match the peaks up to the hydrogen groups. If I'm not correct, would someone be able to explain how to determine peaks from their integration values? 

The integration area provides you with the number of protons corresponding to each signal.

[Violagirl]

The peaks for your IR looked correct. I do believe that the higher energy shifts of the carbonyl are from resonance.

[GoGoGadget]

Thanks guys! Going back to integration, if the the peaks are measured, can it be determined to figure out what peaks belong to what hydrogens if overlapping is going on? I know if you know what your peak is and determine the integration measurement, you can determine the area for one hydrogen by dividing the integration value by the number of hydrogens that you know are present. But for the  NMR for chalcone. there were 6 sets of doublets with overlap and wasn't sure how to assign the peaks according to their integration values from that.