Transcript Using NMR Spectra to Identify Unknowns

Using NMR Spectra to Identify
Unknowns
Identifying Unknowns
• The Markovnicov product is the expected
product
• Predict a proton NMR for the product:
What Product Was Formed?
• Proton NMR not consistent
• Further analysis indicates C5H9ClO formed
• What is the structure?
Step 1: Make data table
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 = -CH2B = -CH2C = -CH2D = -CH3
Step 3: Link pieces together
• Use Splitting
• Use shift
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)
• Piece A must be connected to –Cl because of shift
• Piece A must be connected to methylene because
of n=2
Step 4: Test proposed structure
• Does proposed structure match data?
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
Problem 2: C10H12O2
Problem 3: C10H14O ether
• What should you do with 7ppm and 7.3ppm?
• Signal at 1.9ppm: hard to tell how many peaks
Problem 4: C7H12Cl2
Problem 5: C10H14