NMR spectrum alevel aqa chem

how do you solve this question on page 9? https://www.physicsandmathstutor.com/pdf-pages/?pdf=https%3A%2F%2Fpmt.physicsandmathstutor.com%2Fdownload%2FChemistry%2FA-level%2FTopic-Qs%2FAQA%2FOrganic-II%2F3.15-NMR-Spectroscopy%2FSet-I%2FNMR%20Spectroscopy%20QP.pdf
MS: spectrum 1 is S and the 2nd one is R
i get why the last spectrum is Q but i don't understand how to differentiate between S and R can somebody help

Reply 1

TypicalNerd

Original post by ricecakes1

I’d start by counting the number of carbon environments in each isomer:

P: 6
Q: 5
R: 4
S: 4

S is an ester, so according to the data booklet, it should have a signal between δ = 50 ppm and δ = 90 ppm.

https://filestore.aqa.org.uk/resources/chemistry/AQA-7405-SDB.PDF

If you look carefully at the first two 13C NMR spectra and the signals nearest δ = 50 ppm, you’ll spot the signal nearest 50 ppm is just over it and so is in the range of δ = 50 ppm to 90 ppm, indicating there is an ester and so it must correspond to S (since there are just 4 signals so it cannot be P or Q). This is not true of the signal nearest δ = 50 ppm in the second spectrum, but since there are 4 signals it must correspond to R.

Reply 2

ricecakes1

Original post by TypicalNerd

I’d start by counting the number of carbon environments in each isomer:
P: 6
Q: 5
R: 4
S: 4
S is an ester, so according to the data booklet, it should have a signal between δ = 50 ppm and δ = 90 ppm.
https://filestore.aqa.org.uk/resources/chemistry/AQA-7405-SDB.PDF
If you look carefully at the first two 13C NMR spectra and the signals nearest δ = 50 ppm, you’ll spot the signal nearest 50 ppm is just over it and so is in the range of δ = 50 ppm to 90 ppm, indicating there is an ester and so it must correspond to S (since there are just 4 signals so it cannot be P or Q). This is not true of the signal nearest δ = 50 ppm in the second spectrum, but since there are 4 signals it must correspond to R.