© 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!