1H and 13C NMR spectra of allyl isothiocyanate (AITC) were measured, and the exchange dynamics were studied to explain the near-silence of the ITC carbon in 13C NMR spectra. The dihedral angles α = ∠(C1-C2-C3-N4) and β = ∠(C2-C3-N4-C5) describe the conformational dynamics (conformation change), and the bond angles γ = ∠(C3-N4-C5) and ε = ∠(N4-C5-S6) dominate the molecular dynamics (conformer flexibility). The conformation space of AITC contains three minima, Cs-M1 and enantiomers M2 and M2′; the exchange between conformers is very fast, and conformational effects on 13C chemical shifts are small (νM1 - νM2 < 3 ppm). Isotropic chemical shifts, ICS(γ), were determined for sp, spx, and sp2 N-hybridization, and the γ dependencies of δ(N4) and δ(C5) are very large (10-33 ppm). Atom-centered density matrix propagation trajectories show that every conformer can access a large region of the potential energy surface AITC(γ,ε,...) with 120° < γ < 180° and 155° < ε < 180°. Because the extreme broadening of the 13C NMR signal of the ITC carbon is caused by the structural flexibility of every conformer of AITC, the analysis provides a general explanation for the near-silence of the ITC carbon in 13C NMR spectra of organic isothiocyanates.
- Carbon,
- Chemical shift,
- Dihedral angle,
- Molecular dynamics,
- Nuclear magnetic resonance spectroscopy,
- Potential energy,
- Quantum chemistry,
- Allyl isothiocyanate,
- Conformation change,
- Conformational dynamics,
- Conformational effect,
- Exchange dynamics,
- Isothiocyanates,
- Isotropic chemical shifts,
- Structural flexibilities,
- Conformations,
- allyl isothiocyanate,
- carbon,
- allyl compound,
- isothiocyanic acid,
- isothiocyanic acid derivative,
- atom,
- carbon nuclear magnetic resonance,
- chemical bond,
- chemical structure,
- conformational transition,
- density,
- chemistry,
- conformation,
- nuclear magnetic resonance spectroscopy,
- quantum theory,
- Allyl Compounds,
- Carbon,
- Carbon Isotopes,
- Isothiocyanates,
- Magnetic Resonance Spectroscopy,
- Models,
- Molecular,
- Molecular Conformation,
- Quantum Theory
Available at: http://works.bepress.com/rainer-glaser/84/