Example
A teaching walkthrough — three flavonoids, one formula
How Spectra ranks quercetin, luteolin and kaempferol from 1H and 13C in DMSO-d6, and where a chemist should look next.
We use this case to show the objects you will review in Spectra: a ranked shortlist, a match value, 13C RMSD, and the chemical reason two analogues stay on the desk.
The sample is an unknown in DMSO-d6, measured at 600 MHz, with both 1H and 13C. Status on the card is for review.
Analytical question
Which structures are consistent enough with this 1H and 13C to review, and which close analogue still needs another experiment?
Available data
- Nuclei: 1H and 13C
- Field: 600 MHz
- Solvent: DMSO-d6
- Status: for review
Quality checks
Before treating a similar real case as ready, check referencing to residual DMSO, whether the 13C looks complete, and whether the sample is a single compound.
Ranked candidates
| Rank | Candidate | Match | 13C RMSD |
|---|---|---|---|
| 1 | Quercetin | 0.94 | 1.8 ppm |
| 2 | Luteolin | 0.71 | 3.4 ppm |
| 3 | Kaempferol | 0.66 | 4.1 ppm |
These three closely related flavonoids (two flavonols and a flavone) share the formula C15H10O6. Luteolin is a flavone (no 3-OH). Quercetin and kaempferol are flavonols. The C-3 region is where 13C can separate them.
1 Quercetin Match 0.94 13C RMSD 1.8 ppm
Highest match and lowest 13C RMSD of the three. Open this candidate first and ask which carbons still carry residual. A 0.94 match is a reason to inspect, not to close the case.
2 Luteolin Match 0.71 13C RMSD 3.4 ppm
Same C15H10O6 formula, but luteolin is a flavone: no 3-OH. The C-3 shift is the discriminator against the two flavonols. A larger 13C RMSD is the signal to read that region, not to discard the chemistry.
3 Kaempferol Match 0.66 13C RMSD 4.1 ppm
A flavonol analogue still on the shortlist. This is the neighbourhood that eats expert time: same scaffold, different substitution, residuals that need a human.
Open each row in turn. A high match with a 1.8 ppm 13C RMSD is a reason to inspect quercetin, not a certificate.
Remaining uncertainty
Luteolin and kaempferol remain on the list. Analogues with the same formula are exactly the cases that consume senior time.
Next experiment
If this were a compound you needed to sign, a chemist would typically want a cleaner 13C, an authentic overlay, or a complementary 2D experiment the laboratory already validates.
The chemist decides
Possible outcomes: confirm quercetin against a standard, dereplicate as a known flavonoid, or keep the sample unknown if residuals or chromatography disagree.