Introduction to NMR Spectroscopy and Imaging
Assignments for Chapter 05 Basic 2D Homonuclear Spectrscopy
(COSY)
0. Which are correct among the following statements?
(a) A COSY spectrum can be phased so that both cross peaks and diagonal peaks are
purely absorptive.
(b) The cross peaks of a COSY spectrum can be phased to pure absorptive.
(c) The intensity of a cross peak of a COSY spectrum is decided by chemical shift
difference of the two spins that create the cross peak.
(d) The intensity of a cross peak of a COSY spectrum grows with evolution time.
(e) The typical proton-proton J coupling constant a COSY spectrum can detect is
about 10 Hz.
(f) The intensity of a cross peak in a COSY spectrum depends on the strength of the J
coupling constant between the two spins that create that cross peak.
(g) The projection of a COSY spectrum of a sample is identical with its 1D spectrum.
(h) A COSY spectrum is symmetrical with respect to the diagonal line.
1. Describe the major purposes of two-dimensional spectroscopy.
2. A two-dimensional spectrum has the size of 256 × 512 (F1 × F2). For each t1
increment, it takes 20 minutes to record a spectrum of acceptable S/N. How much
is the total acquisition time needed?
3. Examine the following portion of a 2D COSY spectrum:
F2
F1
What type of spin system does this sub-spectrum most probably correspond to?
4. (1) What is the most unwelcome property of a COSY spectrum? (2) In the
following COSY spectrum, indicate which peak is caused by the coherence
transfer from spin A to spin B.
5. Draw the schematic 1H COSY spectra of pure ethanol and ethanol in an acidic
solvent.
6. What are the major disadvantages of COSY? How can they be mended?
7. There COSY spectra of the following compounds:
Glutamic acid(HOOC(NH2)CHCH2CH2COOH), propyl-butyrate
(CH3CH2CH2COOCH2CH2CH3), 2-Bromobutane (CH3CH2CHBrCH3),
2-butanone (CH2CH2(CO)CH3) are given below. Find the correct COSY
spectrum of each compound.
8. Explain why there is no cross peak between sites 1 and 2 in ortho-carborane.
9. The Karplus equation for determining the dihedral angle between two adjacent
residues in a protein is given by
Assuming that the
3
3
J H N H   6.98cos2 (  60 ) 1.38cos(  60 ) 1.72 ).
J H N H  coupling constant of a residue in a protein measures about
10 Hz, what is likely the value of torsion angle  ? Does HNCαH form cis or trans
geometry?