Crystal structures and phase transitions of 3-chloro-2,2-bis(chloromethyl)propionic acid-1 and 1,3-dichloro-2,2-dimethylpropane

The crystal structure of 3-chloro-2,2-bis(chloromethyl)propionic acid-1 was determined from single crystal data. The compound crystallizes in the acen tric monoclinic space group P2(1). Lattice constants at T = 304 K are alpha = 6.961(1) Angstrom, b = 9.979(2) Angstrom, c = 12.0569(3) Angstrom, beta = 94.01(2)degrees. Structure refinement on 1736 independent reflections yie lded R = 0.041. Two molecules are interconnected by hydrogen bridges to for m dimers. Thermal analysis and temperature dependent X-ray and IR-measureme nts gave no indication of a phase transition in the range 150 K < T < 384 K . An order-disorder phase transition was detected for 1,3-dichloro-2,2-dime thylpropane at TI-->II = 194.3 K, with a plastic cubic phase in the range 1 94.3 K < T < 259.1 K. The lattice constant in space group Fm (3) over bar m is a = 9.24 Angstrom at 220 K with a thermal expansion coefficient alpha(( 200 K)) = 2.6769 x 10(-4) K-1. The entropy at the melting point T, = 259.1 K and at the solid-solid phase transition TI-->II = 194.3 K is rather low g iving strong evidence of a plastic phase. Powder X-ray diffraction pattern in the ordered phase at T = 160 K gave indication of monoclinic symmetry wi th a = 12.27 Angstrom, b = 10.86 Angstrom, c = 10.68 Angstrom, beta = 111.8 degrees. Temperature dependent infrared measurements revealed the conforma tion of the molecule.