The ^1 H and ^13C NMR peaks of guaifenesin are: ^1H NMR (CDCl_3) delta 2.58 (t 1

Question

The ^1 H and ^13C NMR peaks of guaifenesin are: ^1H NMR (CDCl_3) delta 2.58 (t 1H), 3.30 (d, 1H), 3.75 - 3.9 (m, 5H), 4.03 - 4.20 (m, 3H), 6.86 - 7.05 (m, 4H); ^13 C NMR (CDCl_3) delta 56.1, 64.1, 70.4, 72.0, 112.1, 114.8, 121.4, 122.3, 148.2, 149.8. Using the labeled guaifenesin figure that follows, answer these questions: In the ^13C NMR of guaifenesin, what peaks (in ppm) correspond to carbons 4 and 5? What numbered carbons correspond to the peaks between 112.1-122.3 ppm? In the ^1H NMR of guaifenesin, what lettered hydrogen atoms correspond specifically to the triplet at 2.58 ppm and the doublet at 3.30 ppm? Why don't the hydrogen atoms at location H in the figure show up as a singlet?

Explanation / Answer

a) since the 2 carbons are too deshielded due to presence of O atom near the carbon

so 4 should have 149.8 and 5 should have 148.2

( because the + I effect of the CH3 is less at carbon 4 than at carbon 5 due to presence of OH on next carbon to carbon4 )

112.1 = 9

114.8= 6

121.4=7

122.3=8

the reasons are similar to that of the above answer. these are so becase their environment.

b)

J corresponds to the 3.3 ppm doublet

I corresponds to the 2.8 ppm triplet

so as to explain this i would say J has 2 electronegative oxygen as next neighbour

while I has only only 1

c)

because of the different environment faced by the 3 hydrogens of the CH3

this might be due to the ring anisotripic effect and the O atom near envinonment .

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