NMR Spectroscopic Analysis of Strychnine. 1. Assemble and attach your spectra of strychnine neatly as follows:

Transcription

1 ame: MR Spectroscopic Analysis of Strychnine 1. Assemble and attach your spectra of strychnine neatly as follows: a. 1 MR spectrum, expansions, and printed listings of peaks and intensities. Letter the resonances a-v starting on the left (upfield) region of the spectrum and expansions. b. 13 C MR spectrum and expansions. umber the resonances 1-21 starting on the left (upfield) region of the spectrum and expansions. c. 13 C MR DEPT90 and DEPT135 spectra. d. Gradient-enhanced MQC spectrum with 1 and 13 C MR spectra along the axes and expansions so as to be useful in working with the data. Mark the number associated with each letter along the 1 axis of the MQC spectrum and expansions. e. Gradient-enhanced CSY spectrum with 1 MR spectrum along the axes and expansions so as to be useful in working with the data. Transfer the numbers and letters from the MQC spectrum to the axes of CSY spectrum and expansions. Label the crosspeaks in the CSY spectrum and expansions with the numbers and letters. f. Gradient-enhanced MBC spectrum with 1 and 13 C MR spectra along the axes and expansions so as to be useful in working with the data. Transcribe the letters and numbers to the 1 axis. Transcribe the numbers (1-21) to the 13 C axis. g. Gradient E spectra. Label each spectrum to indicate which peak was irradiated (letter and number) and which peaks are enhanced and their approximate enhancements. h. Gradient-enhanced ESY spectrum and expansions. Transcribe the letters and numbers to the axes. i. Gradient-enhanced TCSY spectra and expansions. Transcribe the letters and numbers to the axes. 2. Attach a printout of the molecular model of strychnine that you generated. Try to orient it in a fashion similar to the Chemdraw and model structures shown below. If there are any errors in your connectivity or stereochemistry, please fix them in your model. β α α β α β β α α β α β

2 3. Write the letter of the resonance next to the appropriate proton in the molecule. β α β α α β β α β α β α 4. Write the number of the resonance next to the appropriate carbon in the molecule. β α β α α β β α β α β α

3 5. Tabluate the shifts of the 1 resonances (a-q) in order of descending chemical shift. Provide an appropriate name for each multiplet (e.g., s, d, t, q, quintet, sextet, septet, octet, dd, ddd, dt, td, dddd, tt, qd, dq, etc.) and list its coupling constants in appropriate order; also list its integral [e.g., a: 3.30 (t, J = 7.3 z, 3 )]. If a resonance is not described by a well-defined multiplet, name it as m and give its range [e.g., c: (m, 2 )]. a b c d e f g h i j k l m n o p q r s t u v 6. Write each geminal ( 2 J ) or vicinal ( 3 J ) coupling constant on the red line the corresponding arrow. If any of the coupling constants are very small (e.g., < 1 z) and don't result in splitting, write SM. If the coupling constant is not small but cannot be determined, write D. α β α β α β α β α β α β

4 7. Draw arrows to indicate any additional long-range couplings that you detect either through splitting or in the CSY spectrum. If the coupling constants are very small (e.g., < 1 z) and don't result in splitting, write SM. If the coupling constant is not small but cannot be determined, write D. β α β α β α β α β α β α 8. Which of the coupling constants that you were able to measure would be useful in determining the stereochemistry of strychnine? Draw arrows to indicate the vicinal ( 3 J ) coupling constants that you were able to determine that would be useful in establishing the stereochemistry of strychnine. In PyML, measure the dihedral angle associated with that coupling constant, and write the dihedral angle over the arrow.

5 9. Draw arrows to indicate Es observed between protons on non-adjacent carbons. If the Es are weak or ambiguous indicate this by writing the letter W or A over the arrow. 10. Measure the distances associated with these Es in PyML. Mark the distances associated with these ES and all distances of 3.0 Å or less between protons on non-adjacent carbons. Remember that Es scale as r -6. A 3.0 Å E is about 33% of a 2.5 Å E, and a 3.5 Å E is about 13%.

6 11. Imagine that you had to solve the structure of strychnine from scratch. Draw the structures of all fragments that you can identify from MQC, CSY, and coupling constants or coupling patterns (the "pieces" that we ultimately need to assemble through MBC, judicious consideration of chemical shifts, etc.). 12. Continuing to imagine that you had to solve the structure of strychnine from scratch. Examine the MBC spectrum and identify all of the crosspeaks that would be useful to you in assembling the fragments. Draw arrows to indicate the MBC couplings that you would use to assemble the fragments. β α β α β α β α β α β α