Using NMR Spectra to Identify Unknowns

Identifying Unknowns

• The Markovnicov product is the expected product

• Predict a proton NMR for the product:

O HCl

Cl

O

expected

012345PPM

1H

2H3H

3H

What Product Was Formed?

• Proton NMR not consistent• Further analysis indicates C5H9ClO formed• What is the structure?

01234PPM

2H 2H

2H

3H

Step 1: Make data table

01234PPM

2H 2H

2H

3H

Signal Shift (ppm) Integration Splitting

A 3.7 2 Triplet (n=2)

B 2.7 2 Triplet (n=2)

C 2.5 2 Quartet (n=3)

D 1.1 3 Triplet (n=2)

Step 2: Pieces

• Based on integration, MF• Degrees of unsaturation

for C5H9ClO = 1

Signal Shift (ppm)

Integration Splitting

A 3.7 2 Triplet (n=2)

B 2.7 2 Triplet (n=2)

C 2.5 2 Quartet (n=3)

D 1.1 3 Triplet (n=2)

A = -CH2-B = -CH2-C = -CH2-D = -CH3

C

O

Cl

Step 3: Link pieces together

• Use Splitting• Use shift

• Piece A must be connected to –Cl because of shift• Piece A must be connected to methylene because

of n=2

Signal Shift (ppm)

Integration Splitting

A 3.7 2 Triplet (n=2)

B 2.7 2 Triplet (n=2)

C 2.5 2 Quartet (n=3)

D 1.1 3 Triplet (n=2)

Step 4: Test proposed structure

• Does proposed structure match data?O

Cl

Signal Shift (ppm)

Integration Splitting

A 3.7 2 Triplet (n=2)

B 2.7 2 Triplet (n=2)

C 2.5 2 Quartet (n=3)

D 1.1 3 Triplet (n=2)

Problem 1: C5H10O2 ester

012345PPM

2H

3H

2H

3H

Problem 2: C10H12O2

024681012PPM

s, 3

m, 15

t, 6

t, 6

qn, 6

Problem 3: C10H14O ether

• What should you do with 7ppm and 7.3ppm?• Signal at 1.9ppm: hard to tell how many peaks

012345678PPM

2H

3H 2H

1H

6H

Problem 4: C7H12Cl2

0123456PPM

s, 1H

q, 2H

s, 3H

s, 3H

t, 3H

020406080100120140PPM

Problem 5: C10H14

012345678PPM

1H

1H

2H

4H

6H

020406080100120140PPM