Differential thermal analysis and nuclear quadrupole resonance study on polymorphic 1,4-dichlorobutane

Abstract

Differential thermal analysis (DTA), and the 35Cl nuclear quadrupole resonance (NQR) frequency (v Q ) and line width (Δv Q ) were measured as a function of the temperature in solid 1,4-Dichlorobutane (DCB). Two crystalline modifications forms I and II, stables above and below T c = 210 K respectively were found according to the thermal history of the sample. A comparative analysis of the NQR frequency in both phases suggests that the crystal structure in form II is closer-packed than in form I. The NQR line width shows the existence of a thermal activated process with an activation energy E a ≃ 20 kJ mol−1, probably related with reorientations of the CH2Cl end groups. Some orientational disorder is expected in the low temperature modification since the line width is twice as much as that in the high temperature phase.