Report No xxxx - Instytut Fizyki JÄ drowej PAN

35 Cl- NQR AND 1 H-NMR STUDY OF MOLECULAR DYNAMICS OF
p,p′-DDA INSECTICIDE
K. Makiej, A. Nowacka, J. Kasprzak, R. Utrecht, J. Wąsick, B. Nogaj
Department of Physics, Adam Mickiewicz University, Umultowska 85, 61-614 Poznań,
Poland
INTRODUCTION
The method of Nuclear Quadrupole Resonance (NQR) brings information not only on the
electronic structure of molecules, but also on the motions of the molecules or certain atomic groups.
This method along with the 1 H-NMR have been applied to study molecular dynamics of the insecticide
p,p`-DDA ( 1,1-bis(p-chlorophenyl) acetic acid) [1], belonging to DDT type compounds [2]. The
molecule of this compound takes the shape of a wedge with the base of phenyl rings with chlorine
atoms at the para positions and the COOH group at the top.
EXPERIMENTAL
The compound studied p,p`-DDA was purchased at Polish Chemical Reagents – Gliwice.
35 Cl-NQR measurements were performed on a lab-made pulse Fourier transform NQR spectrometer
operating in the frequency range 20-40 MHz. The 35 Cl-NQR frequencies (ν Q ) and nuclear quadrupole
spin-lattice relaxation times (T 1Q ) were determined in the temperature range 77K- 350.5K.
Measurements of 1 H-NMR spin-lattice relaxation times (T 1 ) were made in the range 100K - 299K on a
laboratory-made pulse spectrometer operating at 60 MHz.
RESULTS AND DISCUSSION
The NQR spectrum of p,p`-DDA shows two 35 Cl-NQR lines assigned to the two chlorine
atoms in the molecule. The frequencies of these lines decrease with increasing temperature, Fig.1.
35.0
34.8
ν Q
[MHz]
34.6
34.4
34.2
34.0
50 100 150 200 250 300 350 400
T [K]
Fig.1. Temperature dependence of 35 Cl-NQR frequency in p,p’-DDA.
The difference in the slope of the ν Q (T) dependencies obtained for the two lines suggests a
dynamical inequivalence of the two phenyl rings in the p,p′-DDA molecule. The values of the nuclear
quadrupole spin-lattice relaxation times (T 1Q ) increase with increasing temperature (Fig.2). From the
slopes of the T 1Q (T) dependencies the activation energies have been found as 3.5kJmol -1 and
3.9kJmol -1 . A similar dependence has been obtained for the nuclear magnetic spin-lattice relaxation
times (T 1 ). It should be noticed, that these values are very high and reach 214 s at room temperature
(Fig. 3). From the slope of the T 1 (T) the activation energy has been calculated as 4 kJmol -1 .
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