The development of synthetic routes for functional chemicals has been heavily depending on experience and intuition of synthetic organic chemists. In case that target molecules have complex structures, there are many possible synthetic routes, and it is often difficult to determine which one should be adopted. In order to decrease synthesis routes for experiments, we introduced “in silico screening” which requires to search TSs for synthesis routes, we have proposed a method to locate the new TS structure of a target reaction by using TS structures in TSDB. However, this method seldom gives the most stable TS structure within possible conformers. That is, the stability of transition states (TS), reactants and products is highly dependent on initial structures used for optimization. Therefore, this method is likely to give inadequate data to compare calculated and measured values of other synthetic reactions. For these purposes, we have to find reaction mechanisms with the most stable TS and molecules involved in the reactions. In this paper, we proposed a method to search the most stable reaction pathway and applied it to the Pinner Pyrimidine reaction of ethyl 3-oxobutanoate and 3-ethoxypropanimidamide.

Solvatochromism of 4-(diethylamino)-4’-nitroazobenzene was observed by visible absorption spectroscopy, and mechanism of the shift of absorption maxima was explained on the basis of semi-empirical molecular orbital calculation results. The wavelength of the absorption maximum measured for methanol solution was longer than that measured for cyclohexane solution; solvatochromic color change was observed. Dipole moments of the ground state and excited state of the azo compound calculated by the CNDO/S method indicated that the excited state was more polar than the ground state. This polarization at the excited state corresponds to so-called charge transfer excitation, and the polarization results in lowering of excitation energy in polar solvent. Similar tendency was also confirmed by the density functional theory calculations. The experiment and molecular orbital calculation carried out in this work were suitable for promoting the understanding of the solvatochromic shift mechanism of absorption wavelength.

The extreme gradient boosting regression (XGBR) method was applied to 245 phenol derivatives in order to establish a regression model to predict their toxicity to Tetrahymena pyriformis. The modeling was done by using the set of “electronic-structure informatics” (ESI) descriptors recently suggested by the present authors. It is shown that the XGBR method is successful in predicting the toxicity of phenols in each class of five modes of action (MOA). A feature importance analysis showed that the different ESI descriptors were found to be important depending on the MOA. Through comparisons with the optimized descriptor set previously suggested by M. T. D. Cronin et al. (Chemosphere., 49, 1201-1221, (2002)), it is shown that the ESI descriptor set, which has been applied to different types of target variables, is of similar quality in regression modeling.