Synergy between Experimental and Theoretical Results of Some Reactions of Annelated 1,3-Azaphospholes

Abstract

Computational calculations have been used successfully to explain the reactivity of the >C=P- functionality in pyrido-annelated 1,3-azaphospholes. Theoretical investigation at the Density Functional Theory (DFT) level shows that the lone pair of the bridgehead nitrogen atoms is involved in extended conjugation, due to which electron density increases considerably in the five-membered azaphosphole ring. The electron density in the azaphosphole is further enhanced by the presence of an ester group at the 3-position making the >C=P- functionality electron-rich. Thus, 1,3-azaphospholo[5,1-a]pyridine, i.e., 2-phosphaindolizine having ester group at the 3-position only does not undergo Diels-Alder (DA) reaction with an electron rich diene, such as 2,3-dimethyl-1,3-butadiene (DMB). However, an ester group at 1-position acts as electron-sink, due to which transfer of the electron density to the >C=P- moiety is checked and DA reaction occurs across the >C=P- functionality. The coordination of the Lewis acid to the carbonyl group at the 3-position raises the activation barrier, while it is lowered remarkably when it is coordinated to the P atom. Furthermore, the attack of 1,3-butadiene on the Si face of the P-coordinated (o-menthoxy)aluminum dichloride complex is a lower activation energy path. Fukui functions could be used to explain relative reactivities of indolizine and 2-phosphaindolizine towards electrophilic substitution reactions.

Transparent nanopaper from nanofibrillated bamboo pulp

“…There are two chlorine atoms linked to the benzene ring of the 3,4-dichlorophenyl isocyanate modified cellulose, and the ester groups are connected to the benzene ring by the nitrogen. The Density Functional Theory level suggests that the lone pair of the nitrogen atoms could take part in extended conjugation; thus, the electron density increases distinctly, and the electron density could be further enhanced if there is an ester group (Bansal et al 2018). All these factors may contribute to the low transmittance over the wavelength range of 200 to 300 nm of the nanopapers made by the modified cellulose.…”