Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: toadesque on May 16, 2010, 05:20:10 PM
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So I have the NMR (I think H-NMR??) of my unknown. Looks like this:
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So how do I read this to explain how I know that my compound is 1-pentyne?
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Peak Data
Hz ppm Int.
202.50 2.262 78
201.69 2.253 99
200.13 2.235 105
198.94 2.222 125
195.75 2.186 180
194.81 2.176 270
192.88 2.154 181
192.19 2.146 375
188.94 2.110 132
187.94 2.099 145
186.00 2.077 208
185.56 2.072 230
175.69 1.962 378
173.19 1.934 443
170.44 1.904 246
157.31 1.757 45
156.81 1.751 42
151.56 1.693 33
150.75 1.684 75
149.38 1.668 139
148.56 1.659 42
145.00 1.620 38
143.31 1.601 127
142.63 1.593 236
141.56 1.581 158
137.00 1.530 75
136.38 1.523 120
135.81 1.517 166
134.75 1.505 211
129.63 1.448 66
128.38 1.434 158
122.19 1.365 43
121.50 1.357 49
96.81 1.081 264
95.88 1.071 443
95.19 1.063 285
89.25 0.997 1000
88.44 0.988 432
82.63 0.923 161
81.56 0.911 261
80.25 0.897 128
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Man I hate when I forget stuff I knew well at one time.
The number of peaks represents the number of unique hydrogens attached to adjacent carbons.
Look at that HUGE single peak at 1, that means that there is a carbon with only ONE hydrogen attached to it, which then means that in order to make up the other 3 bonds, there HAS to be a tripple bond. The reason there has to be a tripple bond and not 3 single carbon-carbon bonds is because the single peak is so massive. If the single peak were smaller, you would know there would be more hydrogens on adjacent carbons.
So look at 1 ppm, single MASSIVE peak, but also two smaller peaks, meaning another carbon with 2 unique hydrogens. So our peaks at 1 ppm is the spectrum for the carbon in between the ones labeled A and B.
Now we have a boatload of stuff happening at 1.5 ppm and 2 ppm.
Looking at 1.5 ppm, there is what looks like a multiplet, which I would attriubute to the carbon labbeled "C" because there are 5 adjacent hydrogens.
The peaks going on at around 2ppm look like either a doublet or triplet, a doublet would nicely explain the "D" carbon, as its adjacent to 2 hydrogens.
Frankly, I'm at a bit of a loss for peaks for every single carbon. On our practice NMR sheets we are given the molecular formula, but not the structure. So I don't see how its possible to look at the spectrum and say, oh, there are 5 carbons. We also usually get nicely circled groups of peaks which say, "doublet, triplet, quadruplet, etc
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So In short, the number of peaks localized at one section means, if you take one carbon, and count the hydrogens off of adjacent carbons, they add up to the number of peaks. I can't tell how many peaks are in those spectrum groups though, because sometimes they look like doublets or triplets or multiplets.
I suggest googling, "How to read an H-NMR" or also youtubing how to
http://academics.keene.edu/rblatchly/OrgoCommon/hand/Spectroscopy/nmr/ReadNMR.pdf
http://www.wfu.edu/~ylwong/chem/nmr/h1/
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Thanks for the detailed response.
Actually we weren't given the structure or the molecular formula. We were simply given the NMR spectra and we have to analyze it to figure out what the unknown compound was. The problem is that I did all the NMR stuff in Organic I and I'm at the end of Organic II now so I completely forgot how to do this, and I was never any good at it anyway.
But yeah thanks for helping out!