A computational (DFT, MP2) and GIAO NMR study of substituent effects in benzenediazonium mono- and dications

BOROSKY, GABRIELA L.; OKAZAKI, TAKAO; LAALI, KENNETH K.

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY

WILEY-V C H VERLAG GMBH

Año: 2011 vol. 2011 p. 1771 - 1775

1434-193X

15N and 13C NMR chemical shifts were computed by GIAO-DFT and GIAO-MP2 and for a series of p-substituted benzenediazonium mono- and dications in order to probe the electronic effects of the substituents on the diazonium moiety. Optimized geometries and N/N vibrational frequencies were also considered for comparison. The GIAO-DFT derived 15N chemical shifts correlate more closely with the experimental values as compared to GIAO-MP2. Energy minimizations at the B3LYP/6-311+G(2d,p), M062X-6-311+G(2d,p), MP2/6-311+G(2d,p), G2(MP2), and CBS-Q levels were carried out. Relative dication stability order HCO+ > HOMe+ > HN(Me)2+ > HOH+ > HCN+ > HNO2+ was derived from isodesmic proton transfer reactions. The Nb-protonated dications were less stable than the corresponding p-R+ dications. Among the regioisomeric Nb-protonated dications (with R = -F, -Cl, and ?CN), those with the R group in the para position were preferred. For the regioisomeric, ring protonated benzenium-diazonium dications, the meta protonated dications were more favored (by DFT and MP2). Influence of the counterion and solvent on the computed 15N-NMR chemical shifts in PhN2+ X- were also assessed.