No abstract

The potential energy surfaces for electrocyclic reactions of hexa-1,3,5-triene were calculated by ab initio molecular orbital methods. The transition states of two electrocyclic reaction pathways (conrotatory and disrotatory) for hexa-1,3,5-triene were obtained. Both transition states are a true transition state. The transition state of the disrotatory pathway is about 11 kcal/mol lower in energy than that of the conrotatory pathway. The reaction path through cis−trans isomerization from cZc-hexa-1,3,5-triene to cyclohexa-1,3-diene was proposed. The conrotatory and the disrotatory reaction pathways were also characterized by the CiLC-IRC method.

Paths of isomerizations of isocyanic acid HNCO into various chain isomers via ring intermediates have been investigated by ab initio MO calculations with the MRD-CI procedure employing the 6-31G** basis sets. Geometry optimizations were accomplished at the RHF, UHF, or CASSCF level of theory. It is found that the isomerization from HNCO to cyanic acid HOCN is energetically the most favorable and that it should proceed via successive 1,2-hydrogen migrations rather than by a single 1,3-hydrogen migration. The overall barrier height is calculated to be 423 kJ mol−1, which is ca. 60 kJ mol−1 higher than the critical energy for the main decomposition channel, HNCO→NH(3Σ)+CO. Implications of the results to the kinetics of the thermal decompostion of HNCO at high temperatures are discussed.

Structure-odour relationship analyses using hierarchical clustering were carried out on a diverse dataset of 47 molecules. These molecules were divided into seven odour categories: ambergris, bitter almond, camphoraceous, rose, jasmine, muguet, and musk. The alignment-independent descriptor EVA (EigenVAlue) was used as the molecular descriptor. The results were compared with those of another kind of descriptor, the UNITY 2D fingerprint. The dendrograms obtained with these descriptors were compared with the seven odour categories using the adjusted Rand index. The dendrograms produced by EVA consistently outperformed those from UNITY 2D in reproducing the experimental odour classifications of these 47 molecules.