h abstract selective 1 h, 1 h decoupling thematic use of ribavirin as an example to illustrate nmr...

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Abstract

Selective 1H,1H decoupling

Thematic use of ribavirin as an example to illustrate NMR principles and techniques

1. Williams, K. R.; King, R. W J. Chem. Educ. 1990, 67, A125-A137.

• UW Oshkosh Chemistry Department

• NSF-ILI Program (USE-9153034) for funds to purchase the JEOL GSX-270 NMR spectrometer

The molecule ribavirin serves as an excellent example for illustrating a variety of NMR principles and instrumental

techniques. Ribavirin was used in a thematic fashion as a recurring example throughout a semester-long interpretative

spectroscopy course. The goal was to provide a familiar molecular framework in which to introduce new concepts and techniques

of increasing complexity. Proton NMR spectra were acquired at 270 MHz (carbon at 67.5 MHz) in DMSO-d6

.

Unique protons & chemical shift

• Multiple functional groups with protons in diverse chemical environments

• Asymmetric structure with four contiguous stereogenic centers

• All protons are unique and give well-resolved 1H NMR signals

• All multiplets are first order, making splitting of analysis straightforward

• Interesting backstory (used clinically to treat serious viral infections)

• Commercially available (~$40/100 mg, TCI America, Aldrich, Acros, etc.)

d e f g h i j k l

Ribavirin serves as a good example to illustrate spin-spin splitting, including inverted splitting tree analysis.

Illustrating splitting and n+1 rule

D2O

+ D2O

a b c d e f g h i j k l H2O

HDO

Deuterium-proton exchange

Example: Irradiate proton g

Splitting in coupled protons k and l affected

g

k/l

ji

f

h

e

d

d e f g h i j k l

O

Hi Hh

HO OH

HdH

NO

N

NHa

CONH2Hg

O

H H

HO OH

HdH

NOH

N N

Ha

CONH21.4%

2.7%

9.2%

a b c d e f g h i j k l H2O

22 °C

40 °C

60 °C

70 °C

74 °C

80 °C

b/c

Coalescence Temperature = 74 °C

b c

AB

C D E F G H

160 140 120 100 80 60ppm

Proton decoupled13C NMR

DEPT 135

CH2CH CH

A/BC

CH3

CH

CH2

d e f gh i j k l

d

e

f

g

hi

j

kl

AB C D E F G H

kl

gf

ed

cb

a

ji

h

HETCOR example

Conformations and 1D NOE

Variable temperature NMR

13C NMR, DEPT

2D Homonuclear NMR1

2D Heteronuclear NMR

H2Oa b c d e f g h i j k l

H-Carbon

H-Oxygen

H-Nitrogen

*

*

*

*

1) Unique protons

2) Chemical shifts

3) Spin-spin splitting

4) H-D exchange

5) Selective decoupling

Hk ddd Hl dt

5.4 Hz

4.3 Hz

11.9 Hz

5.4 Hz

5.4 Hz

11.9 Hz

Ribavirin illustrates how asymmetry and restricted rotation can make protons inequivalent.

The aromatic ring and multiple heteroatoms also make ribavirin a good example for discussing deshielding effects and chemical shifts.

Rotation about ribavirin’s amide bond can be studied at experimentally accessible temperatures.

Ribavirin’s Properties Make it Useful in NMR Education

Brant L. Kedrowski and William F. Wacholtz, University of Wisconsin Oshkosh, Oshkosh, Wisconsin 54901

Summary

6) NOE & conformations

7) Variable temperature NMR

8) 13C NMR, DEPT

9) Homonuclear 2D NMR

10) Heteronuclear 2D NMRO

Hi Hh

HfO OHe

HdHj

NHgO N

NHa

O

N

Hb/c

Hb/c

Hk/lHk/l

doubletstriplet

quartets(approximate)

Ribavirin is useful in teaching the following NMR topics:Students can assign protons d-l definitively by selective decoupling.

Students can assign protons b, c, and e-g as OH or NH through exchange with D2O.

b/c

e/f/g

e/f/g

e/f/g

Conformations of ribavirin can be studied by NOE analysis. Homonuclear 2D techniques introduced with ribavirin.

COSY example

Heteronuclear 2D techniques introduced with ribavirin

Carbon NMR and DEPT techniques can be introduced with ribavirin

inequivalent methylene protons

inequivalent amide protons

Reference

Acknowledgements

O

Hi Hh

HfO OHe

HdHj

NHgO N

NHa

O

N

Hb/c

Hb/c

Hk/lHk/l

OH H

DO OD

HH

NDO N

NH

O

ND

D

HH

OH H

HO OH

HH

NHO N

NH

O

NH

H

HH

ppm

Ribavirin

The effect of temperature on chemical shifts of NH and OH protons is also clearly visible (only NH and OH signals shift upfield with increasing temps)