© 2017 University of Mainz, Institute of Organic Chemistry, NMR facility

Problem of the Month 02/2017

1H-NMR

in CDCl3at 600 MHz

© 2017 University of Mainz, Institute of Organic Chemistry, NMR facility

Problem of the Month 02/2017

• This month’s problem is a mixture of two isomeric compounds with an elemental composition of

C7H14O2.

• It is always a good idea to determine the degree of unsaturation (double equivalents) first.

© 2017 University of Mainz, Institute of Organic Chemistry, NMR facility

Problem of the Month 02/2017

13C-NMR

with broadband

decoupling

at 150 MHz

© 2017 University of Mainz, Institute of Organic Chemistry, NMR facility

Problem of the Month 02/2017

Multiplicity-edited1H,13C-HSQC

© 2017 University of Mainz, Institute of Organic Chemistry, NMR facility

Problem of the Month 02/2017

• The edited HSQC shows 1H,13C coupling over one bond and also encodes CH3 and CH groups as

positive signals (red) and CH2 groups as negative signals (blue).

• The mixture consists of a major component and a minor component. Try using the 1H integrals to

determine which signals belong to which of the two components.

• Now use the HSQC to assign the carbon signals from the 13C spectrum to each component.

• Did you notice how the HSQC resolves the overlap of the multiplet at δH 0.91 ppm?

© 2017 University of Mainz, Institute of Organic Chemistry, NMR facility

Problem of the Month 02/2017

1H,13C-HMBC

© 2017 University of Mainz, Institute of Organic Chemistry, NMR facility

Problem of the Month 02/2017

• The HMBC shows 1H,13C coupling over two to four bonds.

• The signals δH 2.04/2.03 ppm are singlets in both compounds and must be connected to a

quaternary carbon due to the absence of 1H,1H coupling. Can you determine which?

• Do you know which structural fragment you have with the singlet and the quaternary carbon? If not,

search for the 13C shifts of the fragment on nmrshiftdb.org to get an idea.

© 2017 University of Mainz, Institute of Organic Chemistry, NMR facility

Problem of the Month 02/2017

1H,1H-COSY

© 2017 University of Mainz, Institute of Organic Chemistry, NMR facility

Problem of the Month 02/2017

• Now use the COSY spectrum to connect the aliphatic portion of the two molecules.

• Can you find out how they are connected to the fragment you identified before?

• Can you explain why the CH2 groups give completely different signals in the two molecules?

© 2017 University of Mainz, Institute of Organic Chemistry, NMR facility

Problem of the Month 02/2017

Still no idea?

• Hint: Use the HSQC to deduce the coupling patterns of the overlapping methyl signals at δH 0.91.

• If you cannot find a solution, try to search for the minor component by its 13C shifts on

nmrshiftdb.org - the major component is not yet in the database but should be easy to identify once

you know the minor compound!