L'échelle p<i>K</i><sub>HB</sub> de basicité de liaison hydrogène des amines tertiaires aliphatiques
Bibliographic record
Abstract
The hydrogen bond acceptor strength of 40 tertiary amines has been measured by Fourier transform infrared (FTIR) spectrometry from their 1:1 complexation constant towards 4-fluorophenol in CCl 4 at 25°C (the pK HB scale). Also measured was the frequency shift, Δν(OH), of the ν(OH) band of methanol hydrogen-bonded to these amines. The comparison of the thermodynamic hydrogen bond basicity scale, pK HB , with the spectroscopic one, Δν(OH), and with the Brønsted pK a scale, points to the great sensitivity of pK HB to steric effects. The pK HB scale of tertiary amines extends from 2.71 for quinuclidine to 0.34 for N,N-diisopropyl-3-pentylamine. The main factors governing this important variation (17 kJ·mol 1 on the Gibbs energy scale) are the electron-withdrawing inductive effect and various kinds of steric effects (e.g., opening of the CNC angles and hindrance to OH fixation on the nitrogen lone pair). Infrared (IR) spectra show the attachment of 4-fluorophenol to the nitrile nitrogen of Me 2 NCH 2 C[Formula: see text]N and Me 2 NCH 2 CH 2 C[Formula: see text]N, to the oxygen of N-methylmorpholine, and to the π electrons of (HC[Formula: see text]CCH 2 ) 3 N and (PhCH 2 ) 3 N, in addition to the attachment to the amino nitrogen. In (PhCH 2 ) 3 N, the electron-withdrawing effect of the three benzyl substituents and, mainly, the very important congestion of the nitrogen lone pair reduce the nitrogen hydrogen-bond basicity almost to nothing, so that tribenzylamine, a nitrogen Brønsted base, turns to a π base in hydrogen bonding. From this example, the large differences between the pK HB and pK a scales of organic bases are emphasized.Key words: basicity, hydrogen bonding, tertiary amines, pK HB scale.
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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 | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 0.001 |
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".