Quadrupolar resonance

Nuclear Quadrupolar Resonance. - A variety of dichlorophosphanes have n.q.r. 35C1 resonances whose average for each compound correlate linearly uith the total Taft constants.103 The spectra of a number of po1yf1uoroary1 hexachlorophosphazenes have been studied.104 A n.q.r. study of pentafluorophenyl-... 

Again, the value of X for MQMAS is given in (70), and X = — 1 for STMAS (as for the anisotropic dimension Q2). Using this convention, the apparent shifts of the quadrupolar resonances expressed in ppm are given by... 

Whilst diffraction techniques immediately spring to mind for solid samples, the quadrupolar nature of the heavier halogen nuclei means that a principle technique related to SS NMR spectroscopy is nuclear quadruple resonance spectroscopy.6 For systems with a quadrupole moment, an EFG generates two energy states in the absence of an applied magnetic field.3/7 It is appropriate to start by considering illustrative cases in which SS NMR spectroscopy provides information that the closely related nuclear quadrupolar resonance (NQR) technique does not. 

The nuclear quadrupolar resonances observed for transition metal halides which form molecular crystals are very similar to those observed for the transition metal complex ions, and can also be divided into the same two classes (Table 9). One class again having coupling constants of the order expected from electronegativity considerations, the other having anomalously low ones. 

In solid state. Nuclear Quadrupolar Resonance (NQR) [41] is the standard technique to measure quadrupolar coupling constants, while in gas phase Microwave (MW) spectroscopy [42] can be used for small molecules. The MW quantities, however, are obtained in the inertial frame of the molecule. In liquid state, there is no direct method to obtain QCCs. In some favorable cases, QCC can be obtained from simultaneous studies of non-deuterated compounds using NMR (Ti minima, partially oriented systems, etc). 

Starting from pentoses and hexoses having varied conformations, we can prepare two collections of pyranosyl chlorides, with axial or equatorial chlorine atoms, the analogues of 2.25 and 2.26, respectively. As with 2-chlorooxane, the axial orientation of the chlorine in 2.25 corresponds to the stable conformation of methyl chloromethyl ether. A comparison of the geometrical data in solid state, when available, shows that the axial carbon-chlorine bond is invariably longer than the same bond in an equatorial position. Finally, Fig. 2.6 shows that, according to quadrupolar resonance spectroscopy, these compounds are divided into two groups. 

For sugars substituted by oxygen at C-1, delocalization is more difficult to prove because the quadrupolar resonance spectrum cannot be observed. The atomic polarizability of oxygen, 0.802, places it between fluorine and chlorine, so it seems very unlikely that the anomeric effect would comes from a radically... 

Since the very beginning, nuclear magnetic resonance (NMR)1 and nuclear quadrupolar resonance (NQR) belong to the family of experimental techniques, along with neutron or X-ray diffraction, thermodynamical or spectroscopic techniques, which were used as tools of primary importance in the study of phase transformations. This is because NMR probes, through the coupling of a nuclei having a nuclear spin to its close environment, by different interactions, the chemical and structural nature of the phase under... 

Chemists can legitimately ask the question whether the / values of photo-electron signals really give information about the molecule or the solid itself. Many other experimental techniques perturb the electronic structure of the groundstate much less, such as Mossbauer spectrometry, nuclear magnetic or quadrupolar resonance, or to a certain extent vibrational spectra obtained by infra-red or Raman methods. Further on, the time-scale of the other techniques tends to be much longer (22) than 10 17 sec of the photo-electron spectra. 

The term non-linear resonance describes the resonant absorption of potential energy from higher-order trapping fields. Such absorption occurs when combinations of an ion s secular frequencies match harmonic sidebands of the RF drive frequency. Conditions for non-linear resonance exist in all QITs but the effect on ion motion is dependent upon the order, sign (+ or -) and strength of the superimposed non-linear fields. Due in large part to the work of Franzen and co-workers [87-92], the phenomenon of non-linear fields and their contribution to non-linear resonance effects in ion traps is now well understood. In addition to the quadrupolar resonance, there are a series of resonance conditions desaibed by Equations 9.11 and 9.12 where V is an integer 0 and n is the order of the multipole. The overall order of the resonance (AO is described by Equation 9.13. 

BCS Bardeen-Cooper-Schrieffer NQR Nuclear quadrupolar resonance... 

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