Related Experiment Video
Updated: May 18, 2026
Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex
Published on: July 27, 2022
Stereodynamics in eight-coordination; a 2D NMR spectroscopic and computational study of the exchange process in
Graham E Ball1, Richard A Andersen
1School of Chemistry, University of New South Wales (UNSW), Sydney, New South Wales 2052, Australia. g.ball@unsw.edu.au
Abstract:
The (13)C{(1)H} NMR spectrum of eight-coordinate ThCl(4)(tmed)(2), where tmed = Me(2)NCH(2)CH(2)NMe(2), shows that two isomers are present at 219.8 K in a ratio of ≈8:1 and inversion of the five-membered Th-tmed ring is slow at this temperature in both isomers. The 2D (13)C{(1)H} exchange spectroscopy (EXSY) spectrum shows that each of the two inequivalent methyl groups of the major isomer does not exchange directly with each other but that they both exchange with both of the two inequivalent methyl groups found in the minor isomer. This implies that interconversion of the two enantiomers of the major isomer proceeds by a stepwise process that involves the minor isomer. The interconversion of the isomers involves a ring-inversion process that may proceed with or without Th-N bond breaking, and the NMR spectra cannot distinguish between these two processes nor can density functional theory (DFT) calculations (B3PW91 and M06 with consideration of dispersion effects and solvent) because these two possibilities proceed by way of transition states of similar energies in this case.
More Related Videos
Related Concept Videos
02:46Crystal Field Theory - Tetrahedral and Square Planar Complexes
Crystal field theory (CFT) is applicable to molecules in geometries other than octahedral. In octahedral complexes, the lobes of the dx2−y2 and dz2 orbitals point directly at the ligands. For tetrahedral complexes, the d orbitals remain in place, but with only four ligands located between the axes. None of the orbitals points directly at the tetrahedral ligands. However, the dx2−y2 and dz2 orbitals (along the Cartesian axes) overlap with the ligands less than the dxy,...
02:52Stereoisomerism
Isomers are different chemical species that have the same chemical formula.
Transition metal complexes often exist as geometric isomers, in which the same atoms are connected through the same types of bonds but with differences in their orientation in space. Coordination complexes with two different ligands in the cis and trans positions from a ligand of interest form isomers. For example, the octahedral [Co(NH3)4Cl2]+ ion has two isomers (Figure 1) In the cis...
02:58Crystal Field Theory - Octahedral Complexes
To explain the observed behavior of transition metal complexes (such as colors), a model involving electrostatic interactions between the electrons from the ligands and the electrons in the unhybridized d orbitals of the central metal atom has been developed. This electrostatic model is crystal field theory (CFT). It helps to understand, interpret, and predict the colors, magnetic behavior, and some structures of coordination compounds of transition metals.
CFT focuses on...
02:42Valence Bond Theory
02:33Stereoisomerism of Cyclic Compounds
01:17Thermal Electrocyclic Reactions: Stereochemistry
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.