The unexpected roles of sigma and pi orbitals in electron donor and acceptor group effects on the C-13 NMR chemical shifts in substituted benzenest

Author(s)

Viesser, Renan V. ; Ducati, Lucas C. ; Tormena, Claudio F. ; Autschbach, Jochen

• Document type: Journal article
• Source: CHEMICAL SCIENCE; v. 8, n. 9, p. 6570-6576, SEP 2017.
• Web of Science Citations: 13

Abstract

Effects of electron-donating (R = NH2) and electron-withdrawing (R = NO2) groups on C-13 NMR chemical shifts in R-substituted benzene are investigated by molecular orbital analyses. The C-13 shift substituent effect in ortho, meta, and para position is determined by the a bonding orbitals in the aryl ring. The pi orbitals do not explain the substituent effects in the NMR spectrum as conventionally suggested in textbooks. The familiar electron donating and withdrawing effects on the pi system by NH2 and NO2 substituents induce changes in the sigma orbital framework, and the C-13 chemical shifts follow the trends induced in the sigma orbitals. There is an implicit dependence of the a orbital NMR shift contributions on the pi framework, via unoccupied pi{*} orbitals, due to the fact that the nuclear shielding is a response property. (AU)

• FAPESP's process: 11/17357-3 - Relationship between molecular electronic structure, NMR parameters and conformational stability
• Grantee: Claudio Francisco Tormena
• Support Opportunities: Regular Research Grants
• FAPESP's process: 13/03477-2 - DOSY methods for analyses of the complex mixtures
• Grantee: Claudio Francisco Tormena
• Support Opportunities: Regular Research Grants
• FAPESP's process: 12/12414-1 - Relationship between molecular electronic structure and heavy atom effect on 13C NMR chemical shift
• Grantee: Renan Vidal Viesser
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 15/20106-3 - Effects of donating and withdrawing electrons groups on 13C NMR shielding tensor in halo-benzenes derivatives
• Grantee: Renan Vidal Viesser
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• FAPESP's process: 15/08541-6 - Nuclear magnetic resonance spectroscopy: beyond molecular structure assignment
• Grantee: Claudio Francisco Tormena
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 14/21930-9 - Study of the solvent effect on the spin spin coupling constant 1JPt-Tl in heavy metal complexes by ab initio molecular dynamics
• Grantee: Lucas Colucci Ducati
• Support Opportunities: Scholarships abroad - Research