Question

13C NMR data provided. When possible, show partial 5. Determine the structure of NMR structures that correspond to individual NMR resonances co 3600 3400 3200 3000 2800 2600 2400 2200 2000 1800 1600 1400 1200 1000 800 31/ 5 AU 1.10 1.05 5.0 4.5 4.0 3.5 3.0 2.5 20 15 10 0 .5 0.0 normal decoupled 'SC DEPT-135: (+) indicates positive peak (-) indicates negative peak * indicates no peak DEPT-90 peaks indicated by Proposed Structure 12 200 180 160 140 120 100 80 60 40 20 0

Answer 1

A strong peak around 1715 cm^-1 indicates the presence of carbonyl group ie., C=O. If the peak is between 1740 - 1720 cm^-1 it could be an aldehyde and if the peak is between 1725 - 1705 cm^-1 it could be a ketone.

A strong peak around 3000 cm^-1 indicates the presence of C-H single bond.

In proton NMR there are 4 different peaks which means the compound contains 4 different hydrogen.

Triplet at 1.05 could be the peak of CH₃ attached to CH₂ ​​​​_. The number of peak in NMR is calculated using (n+1) rule where n is the number of neighbouring hydrogen atoms. Since there are 2 hydrogen in CH_2, the CH₃would give a triplet.

6 protons give a doublet at 1.10 which means these all 6 protons have the same environment. Therefore that group could be (CH₃)₂CH-

2 protons give a quartet at 2.5. This group could be CH₂ attached to CH₃ group. The peak for CH₂ is little bit download field which indicates that the CH₂ is attached to an electronegative group.

One proton gives a multiplet (which contain 7 peaks) suggests that the single proton is surrounded by 6 hydrogen atoms. It is also downfield because that group is attached to an electronegative group. It is because electronegative atom tend to decrease the electron density and thereby reduces the shielding effect. That is the protons are now desheilded and give a peak at downfield.

From C13 NMR we can calculate the number of different types of Carbon atoms. DEPT 90 gives positive peaks for CH. DEPT 135 give positive peaks for CH and CH₃ and a negative peak for CH_2. DEPT will not give any peak for Carbon which do not has hydrogen.

From these information we can conclude that the possible structure could be

CH₃-CH₂-CO-CH(CH₃)₂