35Cl nuclear quadrupole resonance in 3,4-dichloroaniline

JOtJRNAL

OF MAGNETIC

RESONANCE

53, 103-104 (1983)

NOTES ‘% l Nuclear Quadrupole Resonance in 3,4-Dichloromilitw HIROKAZU NAKAYAMA, NOBUO NAKAMURA, AND HIDEAKI CHIHARA Department

of Chemistry, Faculty of Science. Osaka lJnrver.Gty. Tqyonaka, 560. Japan Received August 3 I, 1982

Conflicting results have been reported about the 35Clnuclear quadrupole resonance (NQR) frequenciesof 3,4-dichloroaniline. Bray and Barnes (I) reported two resonance lines corresponding to the number of chemically inequivalent chlorines in the m o lecule. Nagarajan and Murty (2) reported only one line at room temperature, the other resonance line obviously m issing. In 1970, Kantimati (3), on the other hand, observed four frequencies at 90 K and two frequencies at room temperature. Exa m ination of the resonance frequencies as a function of temperature led him to conclude that there must be a second-order phase transition between 143 and 160 K. To resolve such discrepancies and to study the nature of the phase transition in the 3,4-dichloroaniline crystal, if there is any, we carried out differential thermal analysis and measured the 35Cl NQR frequencies as a function of temperature on this material. Measurements were m a d e under various experimental conditions. The commercial material was used with or without purification by vacuum sublimation. Each specimen was m e lted in a glassa m p u le and fused and subjected to three di@erent cooling procedures. In the first procedure, the liquid was quenched by immersion into liquid nitrogen; in the second procedure, the solid at room temperature was TABLE ‘*Cl

NQR

FREQUENCIES

1

OF X,4-DICHLOROANILINE

AT SELECTED

TEMPERATURES

v/MHz -___ TIK

This work

77

35.87 I 35.672

90

35.844 35.656

150

35.657 35.534

200

35.474 35.406

300

35.110 35.064

Kantimati

Bray and Barnes

Nagarajan and Murty

35.872 35.673 35.840 35.770 35.650 35.590

35.100 35.050 \

(room temp.) 35.11

303.5 103

0022-2364f83

$3.00

Copyright 0 1983 by Academic Prw. Inc. All rights of reprDduct~on in any form reseMd

104

NOTES

FIG. 1. Temperature

dependence

of ‘5C1 NQR frequencies.

quenched by immersion into liquid nitrogen; and in the last, the solid at room temperature was cooled at a rate of 1 K min -I. Irrespective of the specimen and the cooling procedure, the “Cl NQR frequency was the same within the experimental error when measured by use of a Dean type super-regenerative spectrometer. Two resonance lines were found at 35.871 and 35.672 MHz at 77 K. The resonance frequencies we obtained agree with those reported by Bray and Barnes (I) at 77 K and also with those by Kantimati (3) at room temperature as seen from Table 1. At 90 K our two frequencies agree with the two of the four frequencies found by Kantimati. The temperature dependence of the resonance frequencies for the purified sample is shown in Fig. 1. One can see in this figure that each line shows no sign of phase transitions between 77 K and room temperature. The two lines in the present specimens show almost the same temperature dependence as two of the lines Kantimati (3) measured. Hence the two extra lines due to Kantimati must have been spurious ones. The differential thermal analysis on the purified specimen did not show any evidence of even a very small thermal anomaly between 100 K and the melting point, 345 K. Therefore, we conclude that 3,4-dichloroaniline does not undergo any phase transitions between 77 K and its melting point, contrary to what Kantimati predicted. The fact that there are two 35C1resonance lines throughout this temperature range means that all the molecules are crystallographically equivalent. REFERENCES 1. P. J. BRAY AND R. G. BARNES, J. Chem. Phys. 27, 55 1 (1957). 2. V. NAGARAJAN AND C. R. K. MURT~, Curr. Sci. 31,279 (1962). 3. B. KANTIMATI, Indian J. Pure Appl. Phys. 8, 255 (1970).