Influence of stereoelectronic interactions on the 13C NMR chemical shift in iodine-containing molecules

Author(s)

Viesser, Renan V. ; Tormena, Claudio F.

• Document type: Journal article
• Source: JOURNAL OF MAGNETIC RESONANCE OPEN; v. 12-13, p. 9-pg., 2022-12-01.

Abstract

Methyl substitution in ortho position causes a deshielding of 6-7 ppm on the 13C NMR chemical shift of the own methyl group and the carbon nucleus bonded to iodine atom (ipso) in iodobenzene-like molecules. In contrast, the carbon ipso is 3-4 ppm shielded when methyl is in para. To understand how the position of methyl substitution perturbs nuclear magnetic responses in iodobenzene and diacetoxyiodobenzene derivatives, shielding mechanisms are theoretically investigated via density functional theory calculations. We show the relative ortho position between iodine and methyl allows through-space and through-bond interactions to take place, generating additional paramagnetic currents and affecting the spin-orbit coupling propagation. Relevant paramagnetic couplings that explain the para methyl substitution behavior are also presented. Shielding mechanisms discussed here for monomethylated compounds can be summed to predict the 13C NMR chemical shift in multi methyl substituted iodine-containing compounds. (AU)

• FAPESP's process: 20/10246-0 - Nuclear magnetic resonance spectroscopy: from pulse sequences to structural assignments
• Grantee: Claudio Francisco Tormena
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 17/20890-1 - Evaluation of shielding and transmission mechanisms of 1H, 13C and 19F NMR
• Grantee: Renan Vidal Viesser
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• FAPESP's process: 15/08541-6 - Nuclear magnetic resonance spectroscopy: beyond molecular structure assignment
• Grantee: Claudio Francisco Tormena
• Support Opportunities: Research Projects - Thematic Grants