2D NMR on the Λ or Δ-Co(diNOsar)Br3 Products
To further characterize the Λ or Δ-Co(diNOsar)Br3 products
students perform HMQC (Heteronuclear Multiple Quantum
Coherence is a more sensitive NMR experiment which gives
the same information as HETCOR), COSY and NOESY 2D
NMR experiments. The NMR spectra are beautifully resolved,
unlike those of Co(en)3
3+, because the Λ-(or Δ-)Co-
(diNOsar)3+ complex is locked into a single conformation by
the newly added nitro-group-containing caps; Λ-δδδ-Co-
(diNOsar)3+ or Δ-λλλ-Co(diNOsar)3+. The COSY and
HMQC spectra of Λ-Co(diNOsar)3+ and Λ-d12-Co(diNOsar)-
Br3 are shown in Figure 2.
The identification of groups of chemically inequivalent
protons and carbon atoms observed in the 1
H NMR, 13C
NMR, HMQC, and COSY spectra of Λ-(or Δ-)Co(diNOsar)
is straightforward; however, mapping out those sets onto the
3D structure of the molecule and differentiating between the
cap and ethylene bridge protons is more challenging. For