The use of indirectly bonded <sup>13</sup>C‐<sup>1</sup>H (<scp>INCH</scp>) shift correlation spectra for ab initio structure elucidation of natural products and other complex organic compounds; A personal and historical perspective
Bibliographic record
Abstract
Abstract This article reviews the use of long‐range shift correlation spectra for structure elucidation of natural products and other complex organic compounds from the early 1980's to the present. Much of it is written from the personal viewpoint of someone who has been involved in this area of research since its earliest days. The first section covers the early use of long‐range correlation spectra in the 1980's. The second section covers the development of specialized pulse sequences for this type of acquisition. It begins with three 13C‐detected sequences, followed by heteronuclear multiple bond correlation (HMBC) and some modified versions of HMBC and, finally, longer range correlation sequences based on the heteronuclear single quantum multiple bond correlation sequence. The third section covers various sequences designed to distinguish between 2‐bond and longer range 13C‐1H correlations. Unfortunately, none of these can make this distinction for non‐protonated carbons. Only the 1,1‐ADEQUATE sequence can make this distinction but its very low sensitivity limits its usefulness. The next section focuses on ways of avoiding getting incorrect structures of organic compounds, an ongoing problem in natural product research. The last section includes likely short‐term developments and possible long‐term developments in NMR methodology that would be beneficial for small molecule structure elucidation.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.002 |
| Scholarly communication | 0.001 | 0.002 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.006 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".