Coupling constant nuclear quadrupole

The nuclear quadrupole coupling constants (NQCC), e Q (Chapter 2, Section 2.4) monitors the electric field gradient (efg) at the nuclear site, the largest component being given 

NQCCs and NMR shifts together find applications to questions of a and n bonding and of additivity of substituent effects, as in NMR/NQR comparisons of T-donor vs. 7t-acceptor properties made in Co and in resonance. A 

The electronic g tensor of ESR spectroscopy has a similar form to that of the shielding tensor [equation (6) or (13)]. The orbital contribution is given by 

Two of the three constants eqQaa, eqQbb id eqC c were determined from microwave optical double resonance (MODR) spectra of NH2 [1 to 4], microwave absorption spectra of ND2 [5], and by ab initio (UHF) calculations [6]. The third constant follows from eqQaa+ eqQbb + QQcc = 0 [3]- The nuclear quadrupole coupling constants listed in the following table are given in terms of the principle axis system (b C2, c 1 molecular plane). 

Microwave spectroscopy of rotational transitions in PHgD gave an upper limit of 20 kHz to the components epaaQ + eqbbQ QaaQ + eciccQ b, c=principal inertial axes) [10]. 

Experimental results are not available. Ab initio calculations at the SCF level, using a basis set of double-zeta quality augmented by bond functions, yielded the component q (maximum absolute value of all tensor elements) of the electric field gradients and the asymmetry parameters r at the and H nuclei [1]  

The same calculations carried out for ammonia gave coupling constants in good agreement with experimental values [1]. 

Previous theoretical studies at the ab initio SCF level were reported in [2 to 4]. References  

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T. P. Das and E. L. Hahn, Nuclear Quadrupole Resonance Spectroscopy, Academic Press, New York, 1958, 223 pp E. A. C. Lucken, Nuclear Quadrupole Coupling Constants, Academic Press, London, 1969, 360 pp. 

Schwerdtfeger, P., Pernpointner, M. and Nazarewicz, W. (2004) Calculation of Nuclear Quadrupole Coupling Constants, in Calculation ofNMR and EPR Parameters Theory and Applications, (eds M. Kaupp M. Biihl and V.G. Malkin), Wiley-VCH Verlag GmbH, Weinheim, pp. 279-291. 

Table 10 BH HLYP/aug-cc-pVTZ calculated nuclear quadrupole coupling constants /(N) and /(Hal) [MHz] of the complexes XY- -NH3 a ...

Other key properties of these complexes relevant for comparison with experiment are the nuclear quadrupole coupling constants. Theoretical NQCC values, as calculated via electric field gradients, are discussed exhaustively in several recent theoretical investigations [26,28,30,33,34] and in experimental work [4-11]. BH HLYP/aug-cc-pVTZ calculated NQCCs [30,34], as evaluated for XY- -NH3 complexes, are listed in Table 10. 

In Sect. 2, it was indicated that changes AXap(X) and A/ / (Y) in halogen nuclear quadrupole coupling constants xap X) and Xafs(Y) of a dihalogen... 

We assume that, on formation of B- XY, a fraction 5j (i = intermolecular) of an electronic charge is transferred from the electron donor atom of Z of the Lewis base B to the npz orbital of X and that similarly a fraction 5p (p = polarisation) of an electronic charge is transferred from npz of X to n pz of Y, where z is the XY internuclear axis and n and n are the valence-shell principal quantum numbers of X and Y. Within the approximations of the Townes-Dailey model [187], the nuclear quadrupole coupling constants at X and Y in the hypothetical equilibrium state of B- -XY can be shown [178] to be given by ... 

Fig. 20 Variation of the fraction <5 of an electronic charge transferred from B to XY on formation of B- XY with the ionisation energy 7b of B for the series XY = 02, BrO and IO. See text for the method of determination of Si from observed XY nuclear quadrupole coupling constants. The solid curves are the functions <5 = A exp(- al ) that best fit the points for each series B- XY. Data for B- -B are nearly coincident with those of B- BrO and have been excluded for the sake of clarity...

Because the atoms occupy highly symmetric lattice positions, anisotropic parameters such as chemical shift anisotropy (CSA) or nuclear quadrupole coupling constants (NQCC) are either zero or fairly small. 

Preliminary Cu-ENDOR results on Cu(salen) show that the nuclear quadrupole coupling constant of the copper ions lies in the range between those for square planar 04 and S202 coordinated copper complexes177. ... 

Relations Between Nuclear Quadrupole Coupling Constants in Different Expressions of 9 q (Sect. 5.2))... 

Lucken, E. A. C. Nuclear Quadrupole Coupling Constants, New York Academic Press (1969)... 

Values were also reported for the rotational constants, centrifugal distortion constants, and the chlorine nuclear quadrupole coupling constants of the three isotopic species F C1 02, F CF 02, and i F CF 0 0. The molecular dipole moment was found to be 1.722 0.03 D. 

The nuclear quadrupole coupling constant, e Qq, of a singly-bonded chlorine atom, R—Cl, is related to the halogen atom valence p and p orbital populations, a and a , by the equation (7,2)... 

Fig. 5. Sigma orbital populations of the halogen atoms in Group IV tetrahalides obtained from the halogen nuclear quadrupole coupling constants by use of Equation (1) with an = 2.0...

The unpaired electron in these two molecules is now in exactly the right orbital for the present purposes, since d —Px bonding is usually invoked in order to stabilise such antibonding or non-bonding orbitals. As we have seen both the nuclear quadrupole coupling constant and the anisotropic electron-nuclear hyperfine coupling constant are dominated... 

Table 13. Nuclear quadrupole coupling constants and p-orbital populations for the ICr anion and related compounds...

S. Prasad, H.-T. Kwak, T. Clark and P. J. Grandinetti, A simple technique for determining nuclear quadrupole coupling constants with RAPT solid-state NMR spectroscopy. /. Am. Chem. Soc., 2002,18,4964-4965. 

The calculated nuclear quadrupole coupling constants (NQCCs) of in artemisinin 9a and some of its derivatives and the effects of charge density due to the nature of ligands on the NQCC of were described. All calculations were performed at the HF/3-21G level <2005MI366>. 

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