COMPUTATIONAL NICS AND 13C NMR ChARACTERIZATION OF SUBSTITUTION PATTERNS OF C60-nNn FULLERENES (n = 1–12)

Abstract

DFT calculations are applied to evaluate the effects of atomic arrangements of dopant atoms on electronic features of the most stable structures of C 60−n N n(n = 1–12) fullerenes. Our study reveals that 13 C isotropic chemical shifts (δiso) of the nuclei at C–N pentagon–hexagon (ph) junctions appear at downfield values while there are no tangible values of δiso for the nuclei at C–N hexagon–hexagon (hh) junctions; the carbon sites attached to the first neighbors of nitrogen at hh junctions (the second neighboring effect) yield upfield values of δiso. Moreover, compensation between diatropic and paratropic ring currents leads to slightly less negative NICS value in C59N heterofullerene (-3.6) compared to the parent fullerene C60 (-4.25). However, with incorporating more nitrogen atoms into the cage the aromaticity first increases, up to the 66π-system C54N6 and C53N7 , yielding the most negative NICS values of -26.3 and -26.8, respectively, and then decreases so that NICS finally reaches the value of -6.6 ppm for C48N12 heterofullerene. On the basis of distinct value predicted for each heterofullerene, one expects that NICS values may also be useful for identification of the molecules through their endohedral 3 He NMR chemical shifts.