Nuclear Magnetic Resonance (NMR)

• Electron density about a proton nucleus affects it's chemical shift

O H Si H

downfield upfield

! e- density " e- density

deshielded shielded

General Ranges of Chemical Shifts in the 1H NMR

1H NMR Correlations

Type of Proton Formula Chemical Shift (!)

•Protons on Carbon

alkane

R-CH3

R2-CH2

R3-CH

0.7 - 1.3

1.2 - 1.6

1.4 - 1.8

allylic

R C C C H

1.6 - 2.2

carbonyl

R C C

O

H

2.0 - 2.7

benzylic

C HAr

2.2 - 3.0

alkyl halide

C HR

I

C HR

Br

C HR

Cl

2.0 - 4.0

2.5 - 4.0

3.0 - 4.0

alkynyl

R C C H

2.5 - 2.7

amine

C HR

NR2

2.2 - 2.9

ether

C HR

OR

3.3 - 4.0

1H NMR Correlations (cont.)

Type of Proton Formula Chemical Shift (!)

•Protons on Carbon (cont.)

alcohol

C HR

OH

3.3 - 4.0

ester

R C O

O

C H

3.7 - 4.1

vinylic

R C C H

5.0 - 6.5

aromatic

Ar H

6.5 - 8.0

aldehyde

R C H

O

9.7 - 10.0

•Protons on Heteroatoms

amines

R NH

1.0 - 5.0

alcohols

R OH

1.0 - 5.5

phenols

Ar OH

4.0 - 12.0

carboxylic acids

R C OH

O

10.5 - 12.0

Common Impurities

Impurity Structure Chemical Shift (!)

tetramethylsilane (CH3)4Si 0.0

water H2O 1.5

chloroform CHCl3 7.3

C CH3Cl-CH2

O

1H NMR Spectrum of Chloroacetone

1H NMR Spectrum of Bromoethane

CH3CH2Br

Can Use Pascal's Triangle to Predict Ratio of Intensities in Multiplets

1

1 1

11 2

1 3 3 1

14641

0

1

2

3

4

singlet (s)

doublet (d)

triplet (t)

quartet (q)

quintet/pentet

# adj protons multiplicity ratio of intensities

example: CH3CH2Bra b

predict: a = triplet (1 : 2 : 1)

b = quartet (1 : 3 : 3 : 1)

Com

mon

ly O

bser

ved

Patte

rns

in th

e Pr

oton

NM

R **

1. E

thyl

gro

up

2. Is

opro

pyl g

roup

3. p

ara

Subs

titut

ed A

rom

atic

CH3

CH2

Y

H YC

CH3

CH3 Y

X

HHH

H

** n

ote:

δ w

ill va

ry w

ith X

and

Y

1H NMR Spectra of n-Butylbenzene

13C NMR (CMR)

13C NMR Correlations

Type of Proton Formula Chemical Shift (!)

•Protons on Carbon

alkane R-CH3 0 - 35

R2-CH2 15 - 40

R3-CH 25 - 50

R4-C 30 - 40

alkyl halide

C IR

C BrR

C ClR

-15 - 25

20 - 40

25 - 50

amine

C NR2'R

35 - 50

alcohol or ether

C OHR

C OR'R

50 - 65

alkynyl

R C C R

65 - 90

vinylic

R C C R

100 - 150

nitrile

R C N

110 - 130

aromatic

C

110 - 175

13C NMR Correlations (cont.)

Type of Proton Formula Chemical Shift (!)

•Protons on Carbon (cont.)

amide

R C NR2'

O

160 - 180

carboxylic acid or ester

R C OH

O

R C OR'

O

160 - 190

aldehyde or ketone

R C H

O

R C R'

O

190 - 220

Common Impurities

Impurity Structure Chemical Shift (!)

tetramethylsilane (CH3)4Si 0.0

chloroform CHCl3 77 (triplet)

NMR Spectra of n-Butylbenzene

13C NMR, DEPT-90, and DEPT-135 Spectra of 6-methyl-5-hepten-2-ol

13C NMR spectrum: shows all carbon types

DEPT-90 spectrum: shows only signals for the CH carbons

(not commonly used)

DEPT-135 spectrum: shows positive signals for CH and CH3

carbons; shows negative signals for CH2 carbons

OH

ntotah

Text Box

C8H10O