From the 1H spectrum we know that we have three aromatic hydrogens (integrals and chemical shift values). The 1H chemical shift close to 10 ppm is characteristic of an aldehyde or carboxylic acid ( 13C can be used to determine which of these two organic groups is present in the molecule, alternatively you can quickly assess it by looking at the lack or presence of carbon satellites in the proton spectrum). In the vanillin example, from 1H integrals you get the information about the presence of a CH 3 and its chemical shift (3.8 ppm) suggests that it is bonded to an electronegative atom. While NOESY experiments are not as common for structural assignment as 1H and COSY might be, they are useful to confirm structural assignments and access spatial information. The NOESY spectrum of small molecules in low viscosity solutions are in a regime where the NOE correlations are positive (orange) 2, so it appears with an opposite phase from the diagonal (blue), as can be seen in Figure 1. Vanillin has an aromatic ring with three substituents and using NOESY spectroscopy it is possible to assign the aromatic substitution in the ring. In the case where NOE is experimentally observed, information related to relative stereochemical, and molecule assignment is obtained.įor ease of illustration of NOESY assignment, in this blog we will discuss the interactions in the small and rigid molecule vanillin. 1 The Nuclear Overhauser Effect (NOE) arises from dipole-dipole interactions due to proximity between active nuclei, giving information about the spatial environment when active spins are close in space (< 5 Å). The NOESY ( Nuclear Overhauser Enhancement Spectroscop Y) spectrum allows users to trace out the spatial relationships in the molecule. In this blog we will discuss the NOESY experiment. NOESY and ROESY are examples of experiments that become more important as we start investigating larger molecular scaffolds. As molecules get more complex, as do the suite of experiments that can be used to understand their molecular and conformational structure. Given the superior resolution of our 100 MHz instrument, we can perform structure elucidation on increasingly large molecules.
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