Cocrystallized 1,2-dibromo-4,5-dimethyl-3-nitrobenzene and 1,2-dibromo-4,5,6-trimethyl-3-nitrobenzene

1,2-Dibromo-3-chloropropane.

4,5-Dibromo-1,2-dimethyl-1H-imidazol-3-ium bromide

In the title salt, C(5)H(7)Br(2)N(2) (+)·Br(-), the cation and anion are connected by an N-H⋯Br hydrogen bond. In the crystal, there are inter-calated layers parallel to (10-2) in which bromide ions are located between the cations. Weak inter-molecular C-H⋯Br hydrogen bonds are also observed.

2,3-Dibromo-3-phenyl­propionic acid

In the crystal of the title compound, C(9)H(8)Br(2)O(2), inversion dimers linked by two O-H⋯O hydrogen bonds occur. All of the carbon and oxygen atoms are disordered over two sets of sites in a 2:1 ratio.

The Strongly Regular (45, 12, 3, 3) Graphs

Using two backtrack algorithms based on different techniques, designed and implemented independently, we were able to determine up to isomorphism all strongly regular graphs with parameters v = 45, k = 12, λ = μ = 3. It turns out that there are 78 such graphs, having automorphism groups with sizes ranging from 1 to 51840.

2,7-Dibromo-9,9-dimethyl-9H-fluorene

The title mol-ecule, C(15)H(15)Br(2), has crystallographic m2m site symmetry. As a result, all atoms, except for those of the methyl groups, are exactly coplanar. In the crystal structure, there are weak π-π inter-actions with a centroid-centroid distance of 3.8409 (15) Å between symmetry-related mol-ecules, which stack along the c axis.