Is shielding more of a product of electronegativity than electron donating groups? When it comes to determining the acidity of compounds, its seems like whether or not an atom is electron donating is more important than whether it is electronegative or not.
Shielding NMR
- Thread starter kfcman289
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The phenomena of shielding is due to the electron cloud. It's best to view this as a spectrum from least shielded (most deshielded) to most shielded (least deshielded) aka the chemical shift on an NMR graph. Without really diving into the details, NMR acts on atoms that have an uneven amount of protons or neutrons. When the nuclei is surrounded by a large electron cloud, it shields the nucleus from the magnetic field acting on it. However, electronegativity pulls electron density towards a particular atom and so, relative to the molecule, you have an area that's relatively deshielded now (or partial positive), causing it have a higher chemical shift. Pi electrons also play a role in deshielding as well and the reason for it is a bit more complicated.
You could also relate the chemical shift (those more deshielded) to acidity, but that's simply because of the increasing dipole that is attained due to electronegativity (or hybridization in some cases). In otherwords, the electropositive atom becomes 'hungry' for a lone pair and so essentially, it's more willing to donate the proton attached directly to it, in order to 'feed itself.' That's my weird way of thinking about it.
