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Structure–melting relations in isomeric dibromobenzenes
Author(s) -
Dziubek Kamil F.,
Katrusiak Andrzej
Publication year - 2014
Publication title -
acta crystallographica section b
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.604
H-Index - 33
ISSN - 2052-5206
DOI - 10.1107/s2052520614011445
Subject(s) - monoclinic crystal system , orthorhombic crystal system , melting point , chemistry , crystallography , halogen , molecular symmetry , isochoric process , crystal structure , halide , molecule , inorganic chemistry , organic chemistry , thermodynamics , physics , alkyl
1,4‐Dibromobenzene melts at a considerably higher temperature than the 1,2‐ and 1,3‐isomers. This melting‐point difference is consistent with the molecular symmetry, as described by Carnelley's rule, and with the frequency of Br...Br halogen bonds. The lowest melting point of 1,3‐dibromobenzene correlates with its two symmetry‐independent molecules, indicating their inability to pack closely. Single crystals of 1,2‐ and 1,3‐dibromobenzene have been grown under isochoric conditions in a diamond–anvil cell and at isobaric conditions in a glass capillary. Their structures have been determined in situ by X‐ray diffraction. At 295 K 1,2‐dibromobenzene crystallizes at 0.2 GPa as orthorhombic, space group Pbca , Z ′ = 1, and 1,3‐dibromobenzene at 0.3 GPa as orthorhombic, space group P 2 1 2 1 2 1 , Z ′ = 2. The same crystal phases are formed at ambient pressure by freezing these liquids below 256.15 and 248.45 K, respectively. The third isomer, 1,4‐dibromobenzene, is a solid at room temperature and crystallizes as monoclinic, space group P 2 1 / a . Striking relations between the structures and melting points of the corresponding dibromobenzene and dichlorobenzene isomers have been discussed.