Understanding of the stability of acyclic nitronic acids in the light of molecular electron density theory

Abstract

In the present work, the electronic structure and stability of acyclic nitronic acids were studied. Depending on the different substituents, the analyzed compounds can be classified as pseudo(mono)radical or zwitterionic nitronic acids. ELF topological analysis of the electron density of nitronic acids containing in their structure EWG substituent (-NO₂ (1); –COOCH₃ (2); –NO₂, –CH₃ (5); –COOCH₃, –OCH₃ (6); –NO₂, –H (7); –COOH₃, –H (8)) permits establishing a pseudo(mono)radical electronic structure with a pseudoradical centers at the C1 carbon atom. In turn, ELF analysis of the compounds 3, 4, 9 and 10 containing substituent belonging to the EGD group (-CH₃ (3); –OCH₃ (4); –CH₃, –H (9); –COH₃, –H (10)) and based on the presence of C1–N2 double bond and absence of pseudoradical centre allows for the classification of these compounds as a zwitterionic nitronic acids. Nitronic acids containing EDG substituents in their structure are the most stable among the analyzed nitronic acids. In turn, nitronic acids containing EWG groups are characterized by higher reactivity in chemical reactions compared to other analyzed nitronic acids.