Question

1. How can the NMR spectrum be used to show that there is no starting material left in the products?

2. Can the NMR spectrum be used to determine the ratio of 2-hexanol to 1-hexanol?

3. What produces the peak around 3.65 ppm in the NMR?

Answer 1

1. NMR spectrum is often used to identify the reaction progress. Usually the NMR of initial starting compounds is taken and after the reaction work up, relatively purified product 's NMr is taken. The absencce of peaks corresponding to the reacting substances and new peaks characteristic of the product tells us the reaction is complete. On the other hand, if there are new peaks of the expectedd product along with the starting materials peaks, it shows the presence of unreacted starting material along with product.

2. Yes. In 2-hexanol CH3CH2CH2CH2CH(OH)CH3 , there are two methyl groups at the ends with different chemical environments. So we would see a triplet at around 1 ppm for the C-6 and a doublet slighltly more deshileded for the C-1.

In 1-hexanol , CH3CH2CH2CH2CH2CH2OH , there is only one methyls group which shows nearly at the same place as in 2-hexanol, but the other methyl doublet is misssing here.

3. Usually the signal at 3.65 ppm is due to methyl/ CH2 which is deshielded by adjacent electronegative atom like oxygen , as in case of methyl esters.