Day 2 Information in 1D 1 H NMR Observable Feature in Spectra - - PowerPoint PPT Presentation

Day 2

Information in 1D 1H NMR Observable Feature in Spectra

• 1. number of peaks
• 2. chemical shift (ppm)
• 3. integration of peaks
• 4. splitting pattern

(singlet, doublet etc.)

• 5. coupling constants
• 6. peak shape (sharp or broad)
• 7. presence of other peaks

Structural or purity characteristics

• 1. number of different types of protons
• 2. chemical environment of proton
• 3. ratio of different types of protons
• 4. number of adjacent protons of

different types

• 5. relative orientation of adjacent protons
• 6. exchangeable protons
• 7. purity

• 4. Splitting Patterns

number of peaks = n + 1 n = number of adjacent (equivalent) nuclei

2.144 2.024 1 2 3 4 5

H H H H H

frequency

1 4 1 6 4

quintet

H H H H

frequency

quartet (q)

1 3 1 3

C C C NO2 H H H H H H H

Coupling (Splitting)

Pascal’s triangle

2 1 1 1 1 3 3 1 1 1

singlet doublet triplet quartet

Splitting by two different types of adjacent protons

doublet of doublet J1 J2

10 50 10 40 10 30 10 20 10 10

Splitting by two different types of adjacent protons

Splitting by two different types of adjacent protons

X Y X X X Y X X Y X Y X

Information in 1D 1H NMR Observable Feature in Spectra

• 1. number of peaks
• 2. chemical shift (ppm)
• 3. integration of peaks
• 4. splitting pattern

(singlet, doublet etc.)

• 5. coupling constants
• 6. peak shape (sharp or broad)
• 7. presence of other peaks

Structural or purity characteristics

• 1. number of different types of protons
• 2. chemical environment of proton
• 3. ratio of different types of protons
• 4. number of adjacent protons of

different types

• 5. relative orientation of adjacent protons
• 6. exchangeable protons
• 7. purity

• 5. Coupling constants

H H H H H H H

Jgeminal Jvicinal J1,3 J1,4

12 - 15 Hz 7 Hz 0 Hz 1 - 3 Hz

Heq Hax Hax Heq

axial to axial 8 - 10 Hz

• equat. to axial 2 - 3 Hz
• equat. to equat. 2 - 3 Hz

10 Hz 0 - 2 Hz 17 Hz

N

5 Hz 8 Hz

J1,2 7 - 9 Hz

C C H H H H

trans cis

cinal coupling partners,

Karplus Equation (viscinal coupling)

coupling constant is measure of dihedral angle

Karplus Equation (geminal coupling)

• coupling constant is measure of bond angle

0 - 2 Hz

H H

10 - 12 Hz 12 Hz

H H

Long-Range Coupling

!ccurs through multiple bonds or 345 conformation.

H H CH; ! H H H ! <r H H 4J = 1.5 Hz 4J = 2 Hz 4J = 3 Hz 4J = 7.4 Hz H H H Cl

Coupling (Splitting)

A Little Bit About J

• Coupling constant J is same in both directions for a coupled pair.

H H

Jba

H H

Jab

a a b b

=

!(Ha) !(Hb) same J

3.83 3.65 3.37 1.49 0.90

Cl O

2 4

1 2 3 4

• Coupled peaks are “tipped” toward each other

Magnetic Inequivalence and Splitting

Magnetic and chemical e.uivalence are different:

Cl Cl Ha Ha Hb Hb

Protons are chemically equivalent, so they don’t split one another. Molecule gives 2 H multiplets. But, the equivalent protons have different geometric relationships with other protons. So they are magnetically inequivalent, and split other protons

• differently. (Each signal is a dd.)

a a’ b b’ Ha Hb

Non-first order behavior

Putting it all together (Example 1)

12 Hz 18 Hz 18 Hz 12 Hz 7 Hz 7 Hz 7 Hz

Example 2

OH

1 2 3 4 5 6 7 8 9 10

1H 1H 1H 1H 1H 2H 3H 3H 3H 2H

Example 2 cont.

ppm 5.0 5.5 6.0

22.77 77.23 5.970 5.917 5.884 5.830 5.245 5.239 5.159 5.151 5.077 5.071 5.023 5.115 5.109 5.101 5.017

OH H H 1 2 3 4 5 6 7 8 9a 9b 10

200 MHz H NMR spectrum of linalool, 5-6 ppm region.

1

200 MHz H NMR spectrum of linalool, 5-6 ppm region.

1

Proton Coupled to: Coupling constant (J): 4 5 (x2) 1.4 Hz 8 9a 9b 10.6 Hz 17.2 Hz 9a 8 9b 10.6 Hz 1.4 Hz 9b 8 9a 17.2 Hz 1.4 Hz

Example 3