Question

2. Below are the aromatic regions for the proton NMR spectra for four isomers of dimethoxybenzaldehyde. These isomers are: 2,4-dimethoxybenzaldehyde, 2,5-dimethoxybenzaldehyde, 2,6-dimethoxybenzaldehyde, and 3,4 dimethoxybenzaldehyde. Draw the structure responsible for each spectrum in the box to the right of the spectra. To help in solving this problem, remember that aldehyde groups are electron withdrawing through resonance. Therefore, nearby protons would be deshielded. On the other hand, methoxy groups are electron donating through resonance. Therefore, nearby protons would be shielded. (10 pts

Answer 1

10.48 7.85 6.80 3,90 3.84 6.74 2,4-dimethoxybenzaldehyde PPM 7.13 7.13 3.93 3.77 7.35 10.19 2,5-dimethoxybenzaldehyde 10 PPM 3.90 10.36 6.94 3.90 7.67 6.94 2,6-dimethoxybenzaldehyde 10 PPM

7.17 7.56 3.83 3.85 7.35 9.61 3,4-dimethoxybenzaldehyde 10 8 6 PPM

b 7 7 a 7 7

a) 2,4-dimethoxybenzaldehyde

b) 2,5-dimethoxybenzaldehyde

c) 2,6-dimethoxybenzaldehyde

d) 3,4-dimethoxybenzaldehyde