solid-state NMR section 1

What is the transition energy of an isolated nucleus?

Y x h x Bo

Y = gyromagnetic ratio of the nucleus

H = the Planck constant

Bo = applied magnetic field strength

What is the transition energy of an isolated nucleus expressed as the Larmor frequency?

V = (y/2pi) Bo

Y = gyromagnetic ratio for nucleus

Bo = applied magnetic field strength

How does shielding affect the transition energy?

Multiply the equation for transition energy by (1 - sigma) where sigma is the shielding of the nucleus by electrons

What is the J coupling?

Another word for it is indirect dipole-dipole interaction

It is the interaction between the magnetic dipole moments of two nuclei

transmitted by their mutual interaction with the magnetic dipole moments of the electrons in the molecule

What is the direct dipole-dipole interaction?

The through space interaction between the magnetic dipole moments of two nuclei

This is averages to zero in liquid state nmr but plays a bigger role in solid state nmr

What are the relaxation times?

T1 = spin-lattice relaxation time (longitudinal)

T2 = spin-spin relaxation time (transverse)

How does rapid molecular tumbling affect liquid state NMR?

Only the isotropic chemical shift and isotropic j coupling are seen in the spectrum and the lines are very narrow

What are the four anisotropic nmr interactions?

Shielding (chemical shift)

Indirect dipole-dipole interaction (J-coupling)

Direct dipole-dipole interaction

Quadrupole interaction

How do the spectra of single crystals and powder samples differ?

Single crystal - the nmr depends on the orientation of the crystal relative to the applied magnetic field so gives defined peaks

Powder - many crystals with random orientations. Spectra is the sum of each of the orientations relative to the applied magnetic field. The spectrum is therefore broad with perpendicular and parallel components

How do the relaxation times affect solid state nmr?

For liquid state NMR, T1 and T2 are about the same, in solid state NMR T2 < < T1

T2 is much shorter for solids so the lines are broader

T1 is much longer for solids so a longer time is needed to measure the spectrum

Minimum T1 occurs when the rate of motion is the same as the Larmor frequency

Why is solid state nmr used?

Gives info on the local structure of the nucleus under study

Study crystalline and amorphous solids

Insight into the molecular motion in solids at various time scales

Info on disorder in solids