NMRanalyst Sample Application: Menthol

Menthol
NMRanalyst Sample Application
Structure Elucidation Without 1D Carbon Spectrum

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Sample Description:

Molecular Formula: C₁₀H₂₀O
Molecular Weight: 156.265

InChI=

1/C10H20O/c1-7(2)9-5-4-8(3)6-10(9)11/h7-11H,4-6H2,1-3H3

IUPAC Name:

2-Isopropyl-5-methylcyclohexanol

CAS Number: 89-78-1
PubChem: 1254
NMRShiftDB: 10008950
Spectrometer: Varian INOVA 500 MHz
Solvent: CDCl₃
Sample Concentration: 2 mg
Applications: Topical analgesic and antipruritic

Provided by:

Dr. Dimitris Argyropoulos, Varian Deutschland GmbH

*.fid/text file specifies: Menthol... 2 mg in CDCl3
*.fid	np	nt	sw	rfp-rfl	ni	sw1	rfp1-rfl1	time

PROTON	8722	4	2302.29	-66.76				17 s
gDQF-COSY	1024	2	2302.82	-67.03	256	2302.29	-66.76	31 m
gHMBC	1024	8	2302.82	-67.03	256	12567.82	0	59 m
gHSQC	920	2	2302.82	-67.03	256	12566.76	0.53	25 m

1D Proton Spectrum:

Top 10 FindIt Molecular Structures Consistent With Molecular Formula and Proton Resonances:

The correct structure is at position 9.


 Best 10 structures in decreasing rating (structure ID shown in parentheses):
    1: 0.955969 (  549904)    2: 0.955904 (  220207)    3: 0.955255 (  231928)
    4: 0.955094 (  147021)    5: 0.954520 ( 1797950)    6: 0.954341 (   62350)
    7: 0.954320 (    7391)    8: 0.954012 (  118129)    9: 0.953956 (    1254)
   10: 0.953956 (  228304)

2D Multiplicity-Edited HSQC Spectrum:

Determined HSQC Correlations:

Top 10 FindIt Molecular Structures Consistent With Proton and Protonated Carbon (HSQC) Resonances:

The correct structure is at position 4.


 Best 10 structures in decreasing rating (structure ID shown in parentheses):
    1: 0.822712 (  380276)    2: 0.819432 (  601420)    3: 0.818544 (  520673)
    4: 0.815891 (    1254)    5: 0.815068 (  200106)    6: 0.812643 (  244711)
    7: 0.810998 (  583664)    8: 0.808390 (  547186)    9: 0.807453 (  618850)
   10: 0.807423 (  119043)

2D DQF-COSY Spectrum:

AssembleIt HSQC & DQF-COSY Derived Carbon-Carbon Correlations:

AssembleIt HSQC & DQF-COSY Derived Correlations

2D HMBC Spectrum:

AssembleIt HSQC, HMBC & DQF-COSY Derived Correlations:

AssembleIt Derived Structure With NMRgraph Added Likely Oxygen Atoms:

only one possible structure

Comments:

For the complete structure elucidation, all menthol carbons are well separated (by at least one ppm). So this structure elucidation does not require a separate 1D carbon spectrum. In general, the HSQC and HMBC spectra should be acquired separating carbons by a fifth of the acquired F1 spectral resolution. Our brucine and strychnine (1mg) demo datasets would need a higher resolution than their acquired 256 HSQC increments. Hence, these two datasets require a separate 1D carbon spectrum. Even then, their HSQC correlation assignments remain unreliable. For menthol, the acquired 256 HSQC increments are actually more than what is needed.

The menthol carbon resonance list can be determined as described for 2-ethyl-1-indanone. After determining the HSQC correlations using the generic carbon list, display the HSQC spectrum with determined correlation areas. Some correlations lie at the F1 spectral edge or along ridges of strong proton resonances. Inspect the integrals.plot plot. Set the Integral threshold for the analysis to 30, an integral threshold clearly outside the noise correlation distribution.

In the final HMBC AssembleIt run, set "Unobserved Bonds" to 1 and "Long-Range HMBC Correlations" to 1. Only one possible structure results, and it is the correct menthol structure.

As a FindIt application, the correct structure is identified from molecular formula, proton, and carbon information.

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