Density functional theory (DFT) calculations on the structures and stabilities of [C<i><sub>n</sub></i>O<sub>2<i>n</i>+1</sub>]<sup>2–</sup> and [C<i><sub>n</sub></i>O<sub>2<i>n</i>+1</sub>]X<sub>2</sub> polycarbonates containing chainlike (CO<sub>2</sub>)<sub><i>n</i></sub> units (<i>n</i> = 2–6; X = H or Li)
Bibliographic record
Abstract
The structures and stabilities of chainlike (CO 2 ) n (n = 2–6) polycarbonates, where adjacent C atoms are linked by C–O–C bonds, were investigated at the density functional theory (DFT) level (B3PW91/6–311G(2d,p)), including dicarboxylic dianions, [C n O 2n+1 ] 2– , and the corresponding acids, [C n O 2n+1 ]H 2 , and Li salts, [C n O 2n+1 ]Li 2 . At equilibrium, the most stable systems have C s , C 2 , or C 2v symmetries. In the gas phase, these dianions are generally metastable with respect to spontaneous ejection of one electron, yet in the presence of counterions they become stabilized, for example, as [C n O 2n+1 ] 2– (Li + ) 2 ion pairs. [C n O 2n+1 ] 2– linkages are also stabilized as dicarboxylic acids, [C n O 2n+1 ]H 2 ; we find the latter to have equilibrium conformations of higher symmetry than previously reported in the literature. To the best of our knowledge, none of the [C n O 2n+1 ]X 2 (X = Li or H) compounds with n ≥ 2 have been reported in the experimental literature (albeit, the alkyl esters C 2 O 5 R 2 and C 3 O 7 R 2 are commercially available). All CO bonds in C 2 O 5 X 2 to C 6 O 13 X 2 have single- to double-bond character (≈140–118 pm), indicating that the [C n O 2n+1 ] moieties are held together by strong chemical forces (in contrast to the weakly bound complexes (CO 2 ) n and (CO 2 ) n – , n > 1). Vibrational frequencies were calculated to ensure all conformations were true minima. The IR and Raman intensities show that the high intensity C=O stretching modes (1750 ± 100 cm –1 ) will help in the spectral characterization of these compounds. Solvation calculations using the polarizable continuum model (PCM) find that C 2 O 5 2– can be formed via CO 3 2– + CO 2 as well as CO 3 – [Formula: see text], each reaction having ΔG 298 < 0 in practically all solvents. This result confirms the experimentally observed large solubility of CO 2 (g) in molten carbonates, CO 3 M 2 (M = Li, Na, or K). In contrast, starting with n = 2, the reactions [C n O 2n+1 ] 2– + CO 2 do not proceed spontaneously in any solvent (ΔG 298 > 0).
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How this classification was reachedexpand
Full frame distilled prediction
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 | 0.004 | 0.003 |
| Meta-epidemiology (narrow) | 0.005 | 0.004 |
| Meta-epidemiology (broad) | 0.004 | 0.002 |
| Bibliometrics | 0.002 | 0.003 |
| Science and technology studies | 0.004 | 0.005 |
| Scholarly communication | 0.001 | 0.002 |
| Open science | 0.003 | 0.001 |
| Research integrity | 0.004 | 0.008 |
| Insufficient payload (model declined to judge) | 0.000 | 0.000 |
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; both teacher heads agree on what is shown here.
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".