Bonding, Aromaticity and Isomerization of Furfuraldehyde through Off-Nucleus Isotropic Magnetic Shielding.

Off-nucleus isotropic magnetic shielding (σ iso (r)) and multi-points nucleus independent chemical shift (NICS(0-2 Å)) index were utilized to find the impacts of the isomerization of gas-phase furfuraldehyde (FD) on bonding and aromaticity of FD. Multidimensional (1D to 3D) grids of ghost atoms (bqs) were used as local magnetic probes to evaluate σ iso (r) through gauge-including atomic orbitals (GIAO) at density functional theory (DFT) and B3LYP functional/6-311+G(d,p) basis set level of theory. 1D σ iso (r) responses along each bond of FD were examined. Also, a σ iso (r) 2D-scan was performed to obtain σ iso (r) behavior at vertical heights of 0-1 Å above the FD plane in its cis, transition state (TS) and trans forms. New techniques for evaluating 2D σ iso (r) cross-sections are also included. Our findings showed that bonds in cyclic and acyclic parts of FD are dissimilar. Unlike the C-O bond of furanyl, the C=O bond of the formyl group is magnetically different. C-C and C-H bonds in furanyl are found similar to those in aromatic rings. A unique σ iso (r) trend was observed for the C 2 -C 6 bond during FD isomerization. Based on NICS(0-2 Å) values, the degree of aromaticity follows the order of cis FD<trans FD<furan<TS FD.