Kinetics and Thermodynamics of the Monomer−Dimer Equilibria of Dialkoxydibutylstannanes
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Bibliographic record
Abstract
Enthalpies and entropies of dimerization have been determined as functions of concentration for dibutyltin dipropoxide, dibutyltin dibutoxide, and dibutyltin diisopropoxide in toluene- d 8 and cyclohexane- d 12 solutions from the variation in 119 Sn NMR chemical shifts with temperature. The values of Δ H and Δ S obtained in toluene- d 8 for dibutyltin dibutoxide were −69.5 ± 3.0 kJ mol −1 and −197 ± 10 J mol −1 K −1, respectively, and for dibutyltin diisopropoxide −67.1 ± 1.4 kJ mol −1 and −244 ± 9 J mol −1 K −1, respectively. Enthalpies and entropies of activation for this process for dibutyltin diisopropoxide have been derived by simulation of the temperature-dependent broadening of the 119 Sn NMR spectra. The free energy of activation for dimerization was 33 kJ mol −1 . The same thermodynamic parameters for a greater range of dibutyltin dialkoxides were derived theoretically by using MP2 single-point calculations on B3LYP-optimized geometries using the LANL2DZdp basis set with diffuse and polarization functions and its effective core potential for tin and 6-311G(2d,p)//6-31G(d,p) for other atoms. Quite good agreement with the experimental results was achieved with this level of theory. The present study confirms that steric effects dictate the degree of dimerization for dibutyltin dialkoxides, with monomers becoming favored at room temperature when the alkoxide groups are changed from primary to secondary.
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Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| 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) | 0.002 | 0.000 |
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Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
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