Search results
Results from the WOW.Com Content Network
In solid-state NMR spectroscopy, magic-angle spinning (MAS) is a technique routinely used to produce better resolution NMR spectra. MAS NMR consists in spinning the sample (usually at a frequency of 1 to 130 kHz ) at the magic angle θ m (ca. 54.74°, where cos 2 θ m =1/3) with respect to the direction of the magnetic field .
Nuclear magnetic resonance (NMR) spectroscopy uses the intrinsic magnetic moment that arises from the spin angular momentum of a spin-active nucleus. [1] If the element of interest has a nuclear spin that is not 0, [1] the nucleus may exist in different spin angular momentum states, where the energy of these states can be affected by an external magnetic field.
A better alternative to the use of potentially hazardous oxidizers is an NMR tube cleaner (right). It is an apparatus which uses a vacuum to flush solvent and/or a detergent solution through the entire length of the NMR tube. In this apparatus, the NMR tube 1 (with the cap 3 fixed to the base of the NMR tube), is placed upside down on the ...
The spin interaction that is usually employed for structural analyses via solid state NMR spectroscopy is the magnetic dipolar interaction. [8] Additional knowledge about other interactions within the studied system like the chemical shift or the electric quadrupole interaction can be helpful as well, and in some cases solely the chemical shift has been employed as e.g. for zeolites. [9]
Throughout this section, the reduced Planck constant = for convenience.. The product operator formalism is usually applied to sets of spin-1/2 particles, since the fact that the individual operators satisfy = =, where is the identity operator, makes the commutation relations of product operators particularly simple.
On a properly acquired NMR spectrum this is seen as a narrow Lorentzian line (at 4.8 ppm, 20 C). Bulk water molecules are also relatively far from magnetic field perturbing macromolecules, such that free water protons experience a more homogeneous magnetic field, which results in slower transverse magnetization dephasing and a longer T 2 * .
The spin population effect increases the signal by a factor of K = ratio of gyromagnetic ratios γ I /γ S of the nuclei, where γ I and γ S are the gyromagnetic ratio of the proton (the I spins) and the low-sensitivity nuclei (the S spins) respectively. Nuclei with higher magnetogyric ratio generally relax more quickly.
The latter is the important term which is responsible for transferring magnetization from one spin to the other and gives rise to the nuclear Overhauser effect. In an NOE experiment, the magnetization on one of the spins, say spin 2, is reversed by applying a selective pulse sequence. At short times then, the resulting magnetization on spin 1 ...