5. Conclusions
This investigation represents the study of various non-competitive and competitive reactions utilizing QTAIM and stress tensor analyses. Examination of four reactions in order to distinguish and quantify the TSIC and TSOC paths were performed. In this framework, we have used four disparate cyclobutenes skeleton-based named 1-chlorocyclobut-1-ene, 3-chloro-4-methylcyclobut-1-ene, 3-methoxy-4-methylcyclobut-1-ene, 3-chloro-4-methoxycyclobut-1-ene that identified as Reactions (1-4) respectively. The results from the exploration of QTAIM and stress tensor scalar reveal that each reaction response differently by showing degeneracy or non-degeneracy of the plots. Generally, we conclude that the ξ(r b) and the ℙσ would be useful indicators to predict whether the reaction is competitive or non-competitive following the degeneracy of the results. Overwhelmingly, the determination of these four reactions display that Reaction 1 is a competitive reaction whilst in contrast Reaction 2 , Reaction 3 , and Reaction 4 are non-competitive reactions. Other stress tensor and QTAIM scalar for instance, the stress tensor eigenvalue λ, the bond-path length (BPL), and the total local energy densityH (rb ) also provided the same results in confirmation with metallicity ξ(r b) and stress tensor polarizability ℙσ. Furthermore, illustration of the metallicity ξ(r b) and stress tensor polarizability ℙσ demonstrate that the maximum values and the transition state points do not occur simultaneously in agreement with transition state theory and our previous investigations for other ring-opening (electrocyclic) reactions.
On the other side of this investigation, we used helicity length H with the purpose of predicting the TSIC or TSOC preferences based on data from experiments. Helicity length H plots for non-competitive reactions,Reactions (2-4) , could correctly predict the torquoselectivity preferences of either TSIC or TSOC. As a result, that the greater helicity lengths H for shared-shell ring-opening BCP s bond-paths could assist to significantly predict both TSIC or TSOC for these three reactions, Reactions (2-4) , exhibit that preference ofReaction 2 is TSOC, Reaction 3 is TSOC, andReaction 4 is TSIC. The advantage of using H is back to where it is constructed. To make it transparent,e2 corresponds to the easiest direction or even mention as the most preferred direction, therefore given that H is constructed from a vector representation of the ellipticity ε, longer values of H for the TSIC or TSOC would predict the path such as torquoselectivity. The other benefit of the variation of H relevant to the shared-shell ring-opening BCP s bond-paths is that instead of only tracking alternation at the BCP it could track slight changes along the length of the whole ring-opening bond-path(r ).