Hans-Christoph Weiss

The Melting Point Alternation in the Short‐Chain n‐Alkanes: Single‐Crystal X‐Ray Analyses of Propane at 30 K and of n‐Butane to n‐Nonane at 90 K

A less dense packing is observed in the odd-numbered n-alkanes compared to the even-numbered members, which consequently lowers melting temperatures. The reason for this is that the even-numbered n-alkanes have optimal intermolecular interactions at both ends (see the picture on the left), while the odd-numbered ones possess these only at one end-at the other end the intermolecular distances are longer (right).

The melting point alternation in a,w-alkanediols and a,w-alkanediamines: interplay between hydrogen bonding and hydrophobic interactions.

The structural details of a,w-alkanediols and a,w-alkanediamines which are characterized by H bonding and hydrophobic interactions. These systems represent a balance between structural simplicity and interaction complexity, which makes the study of interference between interactions a feasible exercise. The anal. of the crystal structures of diols and diamines revealed the interplay between 2 important intermol. interactions that are possible in these amphiphilic compds., namely, H bonding and hydrophobic interactions. While H bonding and hydrophobic interactions operate in consonance in even members, and therefore culminate in dense packing, they run into geometrical conflicts in odd members, leading to looser packing. Accordingly, the odd members of the diol and diamine series have relatively lower densities and m.ps. than the even members.

A comparative study of the crystal structures of tetrahalogenated hydroquinones and γ-hydroquinone

gamma-Hydroquinone (1) and its tetrafluoro, tetrachloro and tetrabromo derivatives (2), (3) and (4) adopt crystal structures that have an almost invariant system of O-H.O hydrogen bonds. However, within this O-H.O framework, the four structures display variations that are characteristic of the C-H, C-F, C-Cl and C-Br groups. In the parent compound (1) aromatic rings are packed with a herringbone geometry, whilst in the halogenated derivatives (3) and (4), polarization-type halogen.halogen contacts are optimized. The fluoro derivative (2) is exceptional in that neither of the above possibilities is adopted, even though the O-H.O scaffolding does not per se prohibit either of them geometrically.

C–H···π interactions inethynylbenzenes: the crystal structures of ethynylbenzene and1,3,5-triethynylbenzene, and a redetermination of the structure of1,4-diethynylbenzene

The crystal structures of 1,4-diethynylbenzene 1 and 1,3,5-triethynylbenzene 2 show similar packing principles with CH···π (triple bond)-zigzag networks; surprisingly, the packing motif of ethynylbenzene 3 is quite different.

CH···π versus CH···Halogen interactions—the crystal structures of the 4-halogenoethynylbenzenes

The crystal structures of the 4-halogenoethynylbenzenes are quite similar and exhibit CH···π interactions, whereas the structure of 4-fluoroethynylbenzene has very interesting and rare intermolecular CH···F contacts.

1,2-Ethanediol (Ethylene Glycol) at 130K

A single crystal of the most commonly used antifreezing agent, ethylene glycol (m.p. 261.6 K), was grown in situ at 220 K with the help of a miniature zone melting procedure using an IR-laser beam. Crystallog. data and at. coordinates are given. The structure soln. and refinement followed std. procedures, in which all H atoms were treated without constraints. The mols. have a synclinal conformation (torsion angle O1-Cl-C2-O2 -64.4 Deg) and the packing consists of catamer-like, two-dimensional networks with H bridges parallel to the [100] plane, O...O distances 2.711(1) and 2.730(2) .ANG. and O-H...O angles 176(2), 171(2) Deg.

4-(Triphenylmethyl)phenol-triphenylphosphine oxide (1/1).

In the crystal structure of the title compd., C25H20O.C8H15OP, the components are linked through O-H...O and C-H...O H bonds. The Ph rings of OPPh3 are close packed, while those of 4-(triphenylmethyl)phenol are involved in sextuple embrace type of packing. Crystallog. data are given.