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Ring strain causes planar chirality in tedarenes A and B, two cyclic diarylheptanoids isolated from the marine sponge Tedania ignis. In both molecules, the chiral plane is an olefinic system, which is very rare among natural products. In tedarene A (1), interconversion is too fast to allow isolation of the enantiomeric atropisomers but still slow enough to cause coalescence of some (1)H and (13)C NMR signals at room temperature. In tedarene B (2), which also shows stable central and axial chirality, the two planar diastereomers are in slow equilibrium. Tedarene B is the smallest natural product with central, axial, and planar chirality in the same simple molecule. The identification of planar chirality as the difference between its conformational isomers allowed the use of theoretical prediction of the CD spectrum to determine the absolute configuration of the stereogenic carbon C-9 as well as of the biphenyl chiral axis.

The amine carbamate related equilibrium (RNHCOO − + H 2 O ⇆ RNH 2 + HCO 3 − ) has been investigated with 13 C NMR (Nuclear Magnetic Resonance) spectroscopy for a series of linear primary alkanolamines, and the apparent carbamate decomposition equilibrium constants have been estimated. A quantitative NMR method for the calculation of the concentration of the species formed in solution has been provided, including the assessment of each of the fast exchanging proton species (whose nuclei resonate at the same chemical shifts in the NMR spectra). For this purpose, NMR-based calibration curves were utilized and an alternative method was applied for validation. The overall results showed that the amount of carbamate found at the equilibrium decreased as the length of the carbon chain increased, while the corresponding apparent carbamate decomposition equilibrium constants featured the same order of magnitude (10 −2).

The diamine 3-(Methylamino)propylamine (MAPA) and eight tertiary amines were studied as single and blended aqueous CO2 absorbents at different concentrations and ratios to investigate the reaction mechanisms. After absorption (40 °C) and desorption (80 °C) experiments, quantitative 13 C NMR experiments were performed on each liquid sample.After absorption, the following CO2-derived species were identified and quantified:(bi)carbonate in each amine system; primary and secondary MAPA carbamate, and MAPA dicarbamate in MAPA-systems; tertiary amine carbonate in tertiary amine-systems.Concerning desorption, the main CO2-species removed was (bi)carbonate, followed in the blends by MAPA dicarbamate.Since, after CO2 absorption, the concentration of MAPA dicarbamate was negligible in single MAPA and, in the blends, mainly increased at increasing pKa of the tertiary amines, it is concluded that the tertiary amines increase the availability of MAPA species to react further with CO2. MAPA and tertiary amines appear to influence each other also for the CO2 release.

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