Hydroboration of allyldimethylamine, diallylmethylamine, triallylamine, and diallylmethylphosphane with dimeric 9-BBN yielded the corresponding singly, doubly, and triply Lewis-acid-functionalized intramolecular Lewis pairs. For the singly Lewis-acid-functionalized derivative Me2N­(CH2)3-9-BBN no evidence for the existence of an equilibrium involving an open-chain form was found in solution. For the doubly and triply Lewis-acid-functionalized compounds Me3–x E­[(CH2)3-9-BBN] x [E = N (x = 2, 3), P (x = 2)] a dynamic exchange of the free Lewis-acid functions with an intramolecular Lewis acid base complex was observed and investigated by variable-temperature NMR spectroscopy. The free energies of activation of the exchange processes were determined by the coalescence method and found to be lower for the Lewis-base component nitrogen than for phosphorus. To further understand the exchange process of the Lewis acids at the central Lewis base, transition states for two different exchange mechanisms were considered and searched for.

Recent studies have shown that glyoxal may remain in the particle phase of aqueous aerosol particles upon drying despite the high vapor pressure of pure glyoxal, due to the formation of oligomeric glyoxal water adducts with low vapor pressure. Little is known about the phase state of such particles, even though some studies suggested a semisolid or glassy state for dried aqueous glyoxal solutions. In this study, we performed glass transition temperature (T g) measurements on various aqueous glyoxal systems. We show experimentally that very slow and also fast drying of aqueous glyoxal solutions can indeed lead to the formation of highly viscous semisolid and glassy states, both in bulk as well as in aerosolized samples. T g changes with the solute concentration before drying, with drying rate and in the presence of additional solutes such as ammonium sulfate or ammonium bisulfate, even when they are present only in catalytic amounts. Temperature-dependent measurements show that the equilibration between various glyoxal species upon water addition, mimicking atmospheric water uptake upon rising humidity, can range from hours to days. We use the measured glass transition temperatures to infer dependencies of the aqueous phase equilibria between monomer, dimer, and trimer glyoxal species and their water adducts and support these by infrared spectroscopy. Our results imply that aqueous glyoxal aerosols may form highly viscous states at atmospherically relevant conditions.

Knowledge of the glass transition temperature of molecular compounds that occur in atmospheric aerosol particles is important for estimating their viscosity, as it directly influences the kinetics of chemical reactions and particle phase state. While there is a great diversity of organic compounds present in aerosol particles, for only a minor fraction of them experimental glass transition temperatures are known. Therefore, we have developed a machine learning model designed to predict the glass transition temperature of organic molecular compounds based on molecule-derived input variables. The extremely randomized trees (extra trees) procedure was chosen for this purpose. Two approaches using different sets of input variables were followed. The first one uses the number of selected functional groups present in the compound, while the second one generates descriptors from a SMILES (Simplified Molecular Input Line Entry System) string. Organic compounds containing carbon, hydrogen, oxygen, nitrogen, and halogen atoms are included. For improved results, both approaches can be combined with the melting temperature of the compound as an additional input variable. The results show that the predictions of both approaches show a similar mean absolute error of about 12–13 K, with the SMILES-based predictions performing slightly better. In general, the model shows good predictive power considering the diversity of the experimental input data. Furthermore, we also show that its performance exceeds that of previous parameterizations developed for this purpose and also performs better than existing machine learning models. In order to provide user-friendly versions of the model for applications, we have developed a web site where the model can be run by interested scientists via a web-based interface without prior technical knowledge. We also provide Python code of the model. Additionally, all experimental input data are provided in form of the Bielefeld Molecular Organic Glasses (BIMOG) database. We believe that this model is a powerful tool for many applications in atmospheric aerosol science and material science.

<p>Knowledge of the glass transition temperature of molecular compounds in atmospheric aerosol particles is important for estimating their viscosity, which directly influences chemical reaction kinetics and phase state. While there is a great diversity of organic compounds present in aerosol particles, experimental glass transition temperatures are known of only a minor fraction of them. Therefore, we have developed a machine learning model in Python designed to predict the glass transition temperature of organic molecular compounds based on molecule-derived input variables. The extremely randomized trees (extra trees) procedure was chosen for this objective. Two approaches using different sets of input variables were followed. The first one uses the number of predefined functional groups present in the compound, while the second one generates descriptors from a SMILES (Simplified Molecular Input Line Entry System) string. For improved results both approaches can be combined with the melting temperature of the compound as an additional input variable, if known. The results show that the SMILES-based predictions had a slightly lower mean absolute error (MAE), but both approaches had a similar MAE of about 12-13 K. Furthermore, we also show that its performance exceeds that of previous parametrizations developed of this purpose and performs better than existing machine learning models. We believe that this model is a powerful tool for many applications in atmospheric aerosol science and material science.</p>

Several 1,8,10-functionalised anthracene derivatives and a couple of 1,8,9-functionalised anthracene analogous, bearing alkynyl substituents at positions 1 and 8 were synthesised and their photochemistry investigated in UV irradiation experiments. Almost all compounds could be converted into their 9,10:10′,9′-head-to-tail photodimers completely excluding the formation of the corresponding head-to-head isomers. Working under non-inert conditions led to formation of endoperoxides in some cases. Furthermore, a non-classical [4π+2π] photodimer was obtained from 1,8,10-tris[(trimethylsilyl)ethynyl]anthracene with one of the alkynyl substituents involved in the photoreaction. The 1H and 13C NMR spectra of all classical and non-classical photodimers were compared with those of the endoperoxides identifying characteristic shifts for the atoms at positions 9 and 10. Moreover, solid-state structures were determined for one or more of each representative.