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littlebluebox.01

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« on: October 09, 2020, 02:50:32 PM »
Hi,
I’m a physics undergrad working with dynamic nuclear polarization of spin one targets ( in our labs case, deuterated propanediol). There is a particular mathematical technique to extract the polarization from the NMR signal which is invalid because deuterated propanediol has a quadrupole moment (between the O-D and C-D bonds). I have tried extensive googling to learn what a quadrupole moment is, but still don’t understand the concept. My background chem knowledge includes orgo 1-2, advanced organic, and physics wise I have a bit of electrodynamics. Is there any chance someone could explain what the quadrupole is and why the deuterated propanediol has one vs regular propanediol? Thanks!

Irlanur

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« Reply #1 on: November 06, 2020, 02:30:04 AM »
Maybe a bit late, but anyway.

You know electric charges, and you probably heard about dipoles. A quadrupole is just the next step. In general, you can expand charge densities into multipoles. but a quadrupole is nothing else than an arrangement of 4 charges, with no net charge and no net dipole.

It turns out that nuclei with a spin larger than 1/2 have a quadrupole moment. The energy of a charge is given by it's product with the potential. the energy of a dipole is given by its product with the electric field (the derivative of the potential), and a quadrupole's energy is given by it's product with the electric field gradient (derivative of the electric field).