I asked a question about E/Z ratio calculation, and was provided with this image

Question

I asked a question about E/Z ratio calculation, and was provided with this image. However, I don't understand how the E/Z ratio was calculated. Is this based on the NMR integration values? Also, how does 12.5:1 equal 93:7 ?

Characteristic peaks for your E and Z isomers perhaps the most useful data on the spectrum are the alkene peaks from your products. They are suay downfieid, between 5.5 and 7.5 ppm, just upfield of the aromatic region, but this may vary according to your compound. Assuming there are, two alkene protons on your molecule, each alkene isomer wi11 result. in a set of peaks. o The alkene protons of the E and z 1somers can be differentiated based on their oupling constants. You may recall learning that these are typically s11ght ly 1arger for the E isomer than the z. The E/Z ratio s based on the ratio from the integration of these two peaks. NormaHze the rat so that the sum of each adds up to 10O. (Note: the E isomer first regardless of which is the major product. Calculating the E/z ratio: aatasoaere netletontheheinmetsamernheretaresda geretsahattoomassrondomer rst, look in the alkene region (5.5-7. 5 ppm). There are doublets that correspond to the vinyl ppm there is a larger doublet. If the integration of the smaller doublet comes out to o.08 Crepresent ing a vinyl proton on the minor isomer) and the larger is 1.Oo (major isomer A 1ittle bit farther downfield there is another doublet that integrates to o.os representing the other vinyl proton on the minor isomer. you should expect to have another Targe doub let downjela to correspond to the other alkene proton, but this is in the aromatic regi1on, so for now don't 3 5 worry about it. Notice also that the coupling constant for the larger doublet is,greater than that of the small doublet. This means that' the major product (from the larger doublet) corresponds to the E isomer. Taking this information, the ratio of the integrals of the smaller doublet to the larger is 2.51,and this is the Ez ratio. Normalize this to 100 by doing it as a mole fraction thus 12-5:1 is the same as 93:7

Explanation / Answer

E, Z isomers can distunish By H NMR. E isomer coupling constant J= 11-15 Hz

Z isomers coupling constant J= 7-11 Hz

based on intregration ratio of NMR values of we should calculate E,Z ratio

12.5:1 not equal to 93:7

because 12.5: multiply with 7

then we can get

(12.5:1) x7=87.5:7

87.5:7 not equal to 93:7

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