Bujak Maciej, Podsiadło Marcin, Katrusiak Andrzej
Institute of Chemistry, University of Opole, Oleska 48, 45-052 Opole, Poland.
J Phys Chem B. 2008 Jan 31;112(4):1184-8. doi: 10.1021/jp075491p. Epub 2008 Jan 9.
Isochoric and isobaric freezing of 1,1-dichloroethane, CH3CHCl2, mp=176.19 K, yielded the orthorhombic structure, space group Pnma, with the fully ordered molecules, in the staggered conformation, located on mirror planes. The CH3CHCl2 ambient-pressure (0.1 MPa) structures were determined at 160 and 100 K, whereas the 295 K high-pressure structures were determined at 0.59 and 1.51 GPa. At 0.1 MPa, all intermolecular distances are considerably longer than the sums of the van der Waals radii, and only a pressure of about 1.5 GPa squeezed the Cl...Cl and Cl...H contacts to distances commensurate with these sums. The exceptionally large difference between the melting points of isomeric 1,1- and 1,2-dichloroethane can be rationalized in terms of their molecular-packing efficiency. It has been shown that the location of atoms in molecules affects their intermolecular interactions, and hence their van der Waals radii are the function of molecular structures.
1,1 - 二氯乙烷（CH3CHCl2，熔点 = 176.19 K）的等容和等压冷冻产生了正交结构，空间群为Pnma，分子完全有序，呈交错构象，位于镜面上。CH3CHCl2的常压（0.1 MPa）结构在160 K和100 K下测定，而295 K的高压结构在0.59 GPa和1.51 GPa下测定。在0.1 MPa时，所有分子间距离都比范德华半径之和长得多，只有约1.5 GPa的压力才能将Cl...Cl和Cl...H接触挤压到与这些半径之和相当的距离。同分异构体1,1 - 二氯乙烷和1,2 - 二氯乙烷熔点的异常大差异可以根据它们的分子堆积效率来解释。已经表明，分子中原子的位置会影响它们的分子间相互作用，因此它们的范德华半径是分子结构的函数。
