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# Integration

See how the area under each proton NMR signal can tell us the number of protons in a certain chemical environment. Created by Jay.

## Want to join the conversation?

• How are the 5 protons in the benzene ring in the same environment?
• They aren't, but there is so little difference between them that they appear to be in the same environment.
• how do you integrate when you're just given the lines and not the numbers on the bottom?
• This method doesn't really work for the MCAT exam where calculators are not allowed. It's much easier if you find the total area of all the signals and divide it by the total number of signals (eg. 116.4/10 =11.64). Then divided the area of each signal by 11.64....it's easier and the value is much closer to the actual value (eg. 57.9/11.64 = 60/12 = 5)
• do you mean 'divide by the total number of *protons' ?
(1 vote)
• Why is it that we multiply all the ratios by 2?, is it always 2?
• No, it can be a range of numbers, 1 and 2 will be the most common though. First, you divide all of the integration values by the lowest value; if you get integers, multiply all of them by 1 (aka do nothing); if you get a half number (like 2.5 in the video), multiply by two; if you get x.333, multiply by 3; x.25 by 4; etc.
Once you have these numbers, add them all together. They should add up to the number of hydrogens on your molecule (if your molecule is symmetrical, you might need to multiply by 2 again).
(side note, these will all be rounded values, sometimes heavily rounded)
• What if youre only given the skeletal structure?
• How are there only 3 signals, I thought that the two hydrogen atoms attached to the benzene ring would each have a separate signal due to the fact that one hydrogen atom is closer to an oxygen atom than the other?
• There will be 2-3 different signals in the aromatic region but unless you're given a zoomed in spectrum you will not be able to see these.
Often the aromatic signal is just a mess, rely on the integrations to tell you how many protons there are.
• In our class, we were told that the area under the peaks are exactly proportional to the number of protons, is that wrong?
• No that's right. They're proportional but they won't always be exactly equal to the number of protons.
Sometimes you'll need to adjust the numbers like in this video so that they equal the number of protons in the molecule.
• Since you know that you have ten protons, isn't it easier to add up the area under all the curves, divide by ten, and then use that as the number for a single proton? Then you don't have to guess at the scaling factor. Just divide the area under a single curve by the area for a single proton.