The temperature variation of the nuclear quadrupole resonance frequency in the two compounds 3,4-dichloro nitrobenzene and 4-chloro 2 nitrophenol were analyzed in the light of the Kushida and Brown models. The internal torsional frequencies at each temperature was calculated using Bayer's model with Tatsuzaki correction under a two-mode approximation to obtain the temperature variation of the torsional frequencies in both compounds. The torsional frequencies are seen to lie between 25 cm^{-1} and 85 cm^{-1} in the first compound and between 30 cm^{-1} and 42 cm^{-1} in the case of the second compound. The temperature dependence of the torsional frequencies is linear above 150 K in the first compound and is linear throughout the range 77 K to 350 K in the second. The smaller temperature dependence in the second compound may be the effect of hydrogen bonding in this compound.
The temperature variation of the nuclear quadrupole resonance frequencies in 3,4-dichloro-aniline and 2,6-dichloro-aniline were fitted to three different models available in literature, namely the Kushida model, the Brown model, and a fourth order polynomial. Brown's model with T_0=205 K gave the best fit in the case of both compounds indicating that the temperature dependence of the torsional frequencies cannot be neglected in these compounds. The internal torsional frequencies were evaluated from the nuclear quadrupole resonance data by using a two-mode approximation in a temperature range of 77-300 K for the above two compounds. The torsional frequencies lie in a range of 30-60 cm^{-1} in both compounds and agree closely with the Raman lines obtained in 2,6-dichloro-aniline. The lower frequency mode around 37 cm^{-1} may be associated with the motion around an axis perpendicular to the benzene ring which is present in both compounds.
The temperature dependent ^{35}Cl NQR data of 2,5-dichloro aniline was analysed using a two-mode approximation to yield the internal torsional frequencies in this compound. The torsional frequencies lie in the range 28-70 cm^{-1} and their temperature dependence is non-linear. The two modes obtained lie close to each other and the lower frequency mode obtained around 30 cm^{-1} agrees closely with the results obtained in similar compounds 2,6-dichloro aniline and 3,4-dichloro aniline. This mode can be identified with motion around an axis perpendicular to the ring.
Various metal salts (Na, K, Rb, and NH_4) of monochloro acetic acid were prepared and the ^{35}Cl nuclear quadrupole resonance frequencies were measured at room temperature. A comparative study of nuclear quadrupole resonance frequencies of monochloro acetic acid and its metal salts is carried out. The frequency shifts obtained in the respective metal chloroacetates are used to estimate the changes in the ionicity of C-Cl bond. Further, the changes in the ionicity of C-Cl bond were used to estimate the percentage of intra-molecular charge transfer between respective cation-anion of the metal salts of chloro acetic acid. The nuclear quadrupole resonance frequency is found to decrease with increasing ionicity of the alkali metal ion.
Molecular dynamics (torsional frequencies) in several chlorine compounds were evaluated on the basis of X-ray thermal parameter data and nuclear quadrupole resonance data using Bayer's and Brown's approximation. It was found that the values obtained in both cases are in good agreement. The above approach is a good illustration of the supplementary nature of the data from X-ray studies in relation to nuclear quadrupole resonance studies of compounds in solid state.
Two-dimensional exchange ^{35}Cl nuclear quadrupole resonance spectroscopy for studies of the CCl_3-group reorientation processes in hexachloroethane and chloral hydrate has been applied. Experimental results were interpreted on the basis of the 2D exchange nuclear quadrupole resonance theory, which takes into account the off-resonance irradiation. It has been demonstrated that 2D nuclear quadrupole resonance exchange spectroscopy is appropriate for quantitative studies of exchange processes in molecular crystals containing quadrupolar nuclei. The method is of particular value for the detection of exchange networks in systems with many sites. Thus, detailed information on the exchange pathways within a network of structural isomers can be deduced and a proper assignment of the nuclear quadrupole resonance lines can be made. Temperature dependence of the exchange rate was studied. The mixing dynamics by exchange and the expected cross-peak intensities have been derived.
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