The 1H and 13C NMR peaks of guaifenesin are 1H NMR CDCl3 258

The ¹H and ¹³C NMR peaks of guaifenesin are: ¹H NMR (CDCl₃) 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); ¹³C NMR (CDCl₃) 56.1, 64.1, 70.4, 72.0, 112.1, 114.8, 121.4, 122.3, 148.2, 149.8. Using the labeled guaifenesin figures that follow, answer these questions:

a. 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?

b. Depending on the solvent used to take the ¹H NMR, you can sometimes observe coupling to the protons attached to heteroatoms such as oxygen and nitrogen. In the ¹H NMR of guaifenesin, what lettered hydrogen atoms correspond specifically to the ¹H triplet at 2.58 ppm and the ¹H doublet at 3.30 ppm?

sC numbering: H lettering: 3 A C 2 HO OH4 OH 10 8

Solution

a)

Due to presence of O atom near the carbon, the 2 carbons are too deshielded, 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 .