NMRanalyst Sample Application: Verbenol

Verbenol
NMRanalyst Sample Application
Structure Elucidation Without 1D Carbon Spectrum

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Sample Description:

Molecular Formula: C₁₀H₁₆O
Molecular Weight: 152.233

InChI=

1/C10H16O/c1-6-4-9(11)8-5-7(6)10(8,2)3/h4,7-9,11H,5H2,1-3H3

IUPAC Name:

4,6,6-Trimethylbicyclo[3.1.1]hept-3-en-2-ol

CAS Number: 18881-04-4
PubChem: 61126
NMRShiftDB: 10021322
Spectrometer: Varian INOVA 500 MHz
Solvent: CDCl₃
Sample Concentration: 8 mg

Provided by:

Dr. Charles L. Mayne, University of Utah

*.fid	np	nt	sw	rfp-rfl	ni	sw1	rfp1-rfl1	time

proton	160000	16	10000	-2503.71				2 m 43 s
hmbc	8192	8	4366.10	-414.46	1024	25000	-4314.10	31 h 57 m
hmqc	2048	8	4366.10	-413.81	512	25000	-1830.56	18 h 36 m

1D Proton Spectrum (TMS Resonances Subtracted):

2D HMQC Spectrum:

Determined HMQC Correlations:

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

The correct structure is at position 1.


 Best 10 structures in decreasing rating (structure ID shown in parentheses):
    1: 0.892462 (   61126)    2: 0.792875 (  421322)    3: 0.786969 (  118088)
    4: 0.782868 (  433073)    5: 0.782421 (  556905)    6: 0.776775 (  247518)
    7: 0.775072 (  282018)    8: 0.774000 (   72421)    9: 0.773790 (   91238)
   10: 0.773789 (  247514)

2D Phase Sensitive HMBC Spectrum:

AssembleIt HSQC (HMQC) & HMBC Derived Carbon-Carbon Correlations:

AssembleIt Derived Structure With NMRgraph Added Likely Oxygen Atoms:

Most likely structure (out of 4 possible ones) by agreement with carbon chemical shift prediction

Comments:

Verbenol is a monoterpenoid pheromone.

The verbenol datasets were our first application of using indirect detection spectra. We used to base structure elucidations on a 1D carbon and a 2D INADEQUATE spectrum. Indirect detection methods gain an order of magnitude in sensitivity. But we continued to use the 1D carbon spectrum which is the least sensitive spectrum by now. Eliminating it completes our goal of indirect detection. Several insights result:

It greatly simplifies the structure elucidation when all spectra are acquired with consistent referencing (not the case for this sample). The next best approach is to use the 1D carbon spectrum to adjust the carbon referencing of all spectra. Here it was necessary to use the exhaustive HSQC and HMBC F1 mapping results for referencing corrections. This is tedious and acquiring datasets with consistent referencing is preferable.

Strong ridges at the TMS (0 ppm) and the three methyl carbon frequencies show in the regular HMBC. Adjustment of the single "Ridge" parameter excludes ridge misinterpretations as shown. It would be preferable to acquire this spectrum with Pulse Field Gradient support to simplify the spectral analysis.

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