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A Computational (DFT, MP2) and GIAO NMR Study of Substituent Effects in Benzenediazonium Mono‐ and Dications
Author(s) -
Borosky Gabriela L.,
Okazaki Takao,
Laali Kenneth K.
Publication year - 2011
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.201001655
Subject(s) - chemistry , protonation , dication , chemical shift , isodesmic reaction , substituent , computational chemistry , solvent effects , carbon 13 nmr , moiety , solvent , density functional theory , stereochemistry , molecule , ion , organic chemistry
15 N and 13 C NMR chemical shifts were computed by GIAO‐DFT and GIAO‐MP2 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 werealso considered for comparison. The GIAO‐DFT derived 15 N chemical shifts correlate more closely with the experimental values as compared to GIAO‐MP2. Energyminimizations 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 + > HNO 2 + was derived from isodesmic proton transfer reactions. The N β ‐protonated dications were less stable than the corresponding p ‐R + dications. Among the regioisomeric N β ‐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 15 N NMR chemical shifts in PhN 2 + X – were also assessed.