Lab 3 (Carbon NMR)

How many unique C NMR signals does this compound produce?

8 Signals

1. Terminal alkene carbon

2. Alkene carbon

3. Aryl carbon attached to alkene substituent

4. Equivalent carbons next to that

5. Aryl carbon attached to isopropyl group

6. Equivalent carbons next to isopropyl group

7. Methine carbon on isopropyl group

8. 2 methyl carbons from isopropyl group

How many C13 NMR signals would this compound produce, give approximate chemical shift

4 Unique Signals

1. 2 Methyl Carbons (8-35)

2. 2 Methylene Carbons (15-5)

3. Aryl carbon attached to substituents (110-170)

4. 2 equivalent aryl carbons next to substituent (110-170)

How would you distinguish between these 2 compounds using proton NMR?

The first structure would have a larger coupling constant than the second one since the protons are farther apart

How would you distinguish these compounds based on C13 NMR. Give the most characteristic difference in their spectra

Main difference is the carboxylic acid and aldehyde group

1. Carboxylic acid has a chemical shift of 175-185

2. Aldehyde has a chemical shift of 190-200

What is the C13 chemical shift for an amide?

165- 175ppm

What is the C13 chemical shift for an ester?

165-175 ppm

What is the C13 chemical shift for a carboxylic acid?

175-185 ppm

What is the C13 chemical shift for an aldehyde?

190-200 ppm

What is the C13 chemical shift for a ketone?

205-220 ppm (weak signal bc there is no protons)

A C13 NMR Spectra has the following signals:  10.3, 20.7, 21.9, 65.9, 170.2 ppm. Which compound does this spectrum belong to? Justify your choice showing that the spectrum is consistent with the structure.

Structure A

1. 5 unique signals

2. 170 ppm signal from ester

3. 65.9 ppm signal from C-O carbon

4. 20.7/ 21.9 signals from either methylene or methyl carbon next to carbonyl

5. 10.3 signal from methyl carbon farthest from any oxygens

What should be the multiplicity of the proton at the arrow?

Doublet of triplets, this is because there are 2 different sets of nonequivalent neighboring protons

How many signals should be present in the 13C NMR of the following compounds?

7 unique signals

1. 1 signal for 2 methyl carbons

2. 1 Signal for aryl carbon attached to Nitrogen

3. Equivalent carbons next to that carbon

4. 1 for aryl carbon attached to carbonyl group

5. Equivalent aryl carbons next to that carbon

6. Carbonyl carbon

7. Methyl carbon next to carbonyl

Which of the carbons in the following compound should appear at the value of highest chemical shift?

D, typically carbonyl carbons have high chemical shifts (ketones are the highest)

What should be an approximate chemical shift of the carbon pointed by arrow ?

~170 ppm (remember amide carbonyl is 165-175 ppm)