R. Latz

Acetic acid at 40K

The redetermination of the structure of acetic acid at 40 K provides higher precision of data, reflected in s.u.s which are about one third of those of Nahringbauer [Acta Chem. Scand. (1970), 24, 453–462].

Dipotassium l-Tartrate Semihydrate

The single crystal and powder X-ray diffraction analyses of the title compound, 2K + .C 4 H 4 O 6 2- .0.5H 2 O, are presented. The discussion contains comparisons with the structures of potassium hydrogen tartrate and calcium tartrate tetrahydrate. The title compound belongs to the class of tartrates that are generally ideal for X-ray structure investigations on single crystals within the framework of teaching seminars. The relevance of the powder X-ray diffraction method in the field of wine analysis, with a view to detecting unallowed blending of wines, is emphasized.

6,7-Dimethyltricyclo[3.2.2.0]non-6-ene at 120 K, a [3.2.2]propellane derivative

The title compound belongs to the group of [3.2.2]-propellanes. Bond angles inside the cyclobutane and cyclobutene units involving the carbon atoms C1 and C2 are: C2—C1—C6 89.81 (4), C1—C2—C5 89.93 (4), C2—C1—C4 86.07 (4) and C1—C2—C3 85.93 (4)°.

Redetermination of biphenylene at 130K

Biphenylene is one of the key compounds in the discussion of bond localization in aromatic systems, usually addressed as Mills-Nixon-Effect (Mills & Nixon, 1930; Maksic et al., 1999). A pronounced bond localization due to the Mills-Nixon-Effect in the direction of one of the Kekule forms is established. Compared to the previous structure determination by Fawcett and Trotter (1966) the significance of bond length alternation in respect to the s.u.s in the six membered rings has been dramatically increased.

(E)-3,4-Diisopropyl-2,5-dimethylhex-3-ene at 125K

The title compound, C16H32, belongs to the family of sterically crowded alkenes. The molecule has a normal C3—C4 double-bond length of 1.3686 (14) A. The torsion angles around this bond are in good agreement with the results of force-field calculations.

2,2,3,3-Tetrachloro-1,4-diphenylbicyclo[2.2.0]hexane, a Strained Bicyclic System

The title compound belongs to the family of bicyclo[2.2.0]hexanes. The bond lengths C1—C4 and C3—C4 of the two four-membered rings are significantly longer than the average bond length for such ring systems [1.554 (21) A] which is obviously a result of angular strain. Experimental bond lengths in A: C1—C4 1.607 (3), C3—C4 1.592 (3), C2—C3 1.588 (3), C1—C6 1.577 (3), C4—C5 1.543 (3), C1—C2 1.535 (3), C5—C6 1.535 (4).

cis-8-Methylbicyclo[4.2.0]octa-1,3,5-triene-7-carboxylic Acid at 293K

The molecules of the title compound are associated as dimers by hydrogen bonds H(1)—O(2)′. Additional characteristic atom distances of the dimer: O(1)—O(2)′ 2.650 (3) (intermolecular), H(1)—O(2)′ 1.74 (intermolecular), O(1)—H(1) 0.91, C(10)—O(2) 1.225 (4) and C(10)—O(1) 1.293 (3) A. The C(10)—O(2) bond distance is slightly longer than the standard distance range for such dimers of 1.205 to 1.215 A whereas the C(10)—O(1) bond distance is slightly shorter than the standard distance of 1.308 A.