ENRICH

Theoretical basis for calculating NMR properties

Magnetic shielding constants, referenced to TMS

Averaging for equivalency

Chemical shift averaging NOE averaging (r^-6 / r^-3)

Concept

What we see by NMR is a boltzmann average over NMR timescales:

Conceptual Workflow:

Specific Workflow: We generate lots of structures by random torsions then minimise them using MM as it’s fast in an attempt to find reasonable approximations of all the conformers of the molecule. We then put a subset of these MM minimised structures to get a better approximation of the energy from DFT (workflow below uses a ‘cheap’ and ‘expensive’ DFT) then calculate the NMR parameters (also by DFT)

What is MM? (Not explicity part of auto-ENRICH but the structures we use as start points for DFT optimisations are from MM):

What is DFT?:

Solvents in DFT, explicit then implicit. We always do implicit as explicit is too costly though we lose all localised effects such as hydrogen bonding. Also means that the chemical shifts of a proton that interacts with solvent is nonsense (You should do redundant conformer elimination on H’s on alcohols and amines, ask someone why if you don’t understand why)