In NMR Spectroscopy, why is lower shielding coupled with higher frequency? It's my understanding that less shielding would require lower energy electromagnetic waves to be absorbed by the protons and frequency is proportional to energy. So, shouldn't lower shielding be coupled with lower frequency in an NMR graph?
Don't know (or care) much about what you're talking about (NMR) and am taking the test in a few days. Did well on practice FLs. I somehow believe I will do fine without this information.
But to humor you, shielding is going to increase the energy of those electrons. Instead of being more tightly bound by the nucleus, they are now
pushed out toward the (let's call it) rim of the atom. Therefore, since the electrons are pushed more toward the periphery, they will be easier to remove. Hence, lower energy EM waves are needed to remove them.
You simply use the reverse logic for your question. Without shielding, electrons are more tightly bound to the nucleus. Now you need more energy to remove them. Hence, with
less shielding you need a
higher energy EM wave which corresponds with
higher frequency (as you noted with E=hf).
Have you taken all the chem prereqs? If so, this type of stuff you could sort of just reason out on the exam just based on what you know makes electrons higher/lower in energy. If not, I'm sure by the end of your studies here you should have a much better intuition about this kind of stuff.
