Investigation of the C-Cl Bonds in Trichloroacrylic Acid, Cl 2 C = CClCOOH, by Single Crystal Zeeman Split NQR

The 35 Cl NQR spectrum of trichloroacrylic acid, Cl 2 C = CClCOOH, was studied by single crystal Zeeman NQR spectroscopy at 303 K (high temperature phase I) and at 275 K (low temperature phase II). At 303 K for the = CCl 2 group chlorines it was found eQΦ zz h -1 ( 35 Cl (2) ) = 76.179 MHz, η ( 35 Cl) = 0.1597; eQΦ zz h -1 ( 35 Cl (3) )= 74.693 MHz, η( 35 Cl) = 0.1868 and for the = CClC - group chlorine eQΦ zz h -1 ( 35 Cl (1) ) = 75.145 MHz, η ( 35 Cl) = 0.1568. The difference in the electric field gradients at the stereochemically inequivalent chlorines Cl (2) and Cl (3) is rather large. The asymmetry parameter η ( 35 Cl (1) ) shows an unusual temperature dependence which probably originates from the change of the hydrogen dynamics and position within the dimeric H-bonded unit (Cl 2 C = CClCOOH) 2 during the phase transition