No abstract

The hydrochloride and hydrobromide of l-tryptophan crystallize in the monoclinic space group P21. The cell dimensions of the hydrochloride are: a=7.45, b=5.30, c=14.67 Å, β=98.80°, and those of the hydrobromide are: a=7.64, b=5.41, c=14.58 Å, β=100.47°. There are two molecules in the unit cell. The two compounds are isomorphous. The crystal structure of the hydrobromide was first determined by the heavy atom method with two-dimensional data, and then that of the hydrochloride was refined by three-dimensional least-squares procedure. The molecular and crystal structure is mainly discussed for the hydrochloride here. The average of six C–C bond lengths in the benzene ring is 1.396 Å, that of C–N bond lengths in the indole ring is 1.384 Å. In the carboxyl group, one C–O bond length, 1.147 Å and two O–C–C angles, 106.8° and 125.7° are significantly different from those reported for amino and carboxyl acids so far investigated. The molecule consists of two planes of the carboxyl group and of the indole ring, the planes making an angle of 70.6° with each other. As to the conformation about the C(α)–C(β) bond, C(γ) lies at the gauche position with both of the carboxyl and the amino groups. The molecules are arranged in double layers parallel to the ab plane; the polar layer is held together by a network of the three N–H··· Cl− hydrogen bonds, 3.17, 3.19 and 3.24 Å and one O–H···C1−, 3.04 Å, and in the non-polar layer, the indole rings are packed mainly by van der Waals forces, the shortest C···C and C···N contacts being 3.74 and 3.42 Å respectively.

Tropolone, C7H602, crystallizes in space group P21/e, with a= 7.135, b---12.178, c= 7.122 A, fl= 99.63 ° and Z= 4. The crystal structure was solved by the symbolic addition procedure and refined by the leastsquares method to give the final R value of 0.054 for the 853 observed reflexions. The molecule is essentially planar and exhibits a slight degree of bond alternation in the seven-membered ring. The hydroxyl group makes a bifurcated hydrogen bond with carbonyl oxygen atoms, of which one branch is intramolecular and the other intermolecular. The latter intermolecular branches form a hydrogenbonded dimer. These characteristic hydrogen bonds seem to play a role in increasing the contribution from the dipolar ionic forms to the ground state of the tropolone molecule.

No abstract

No abstract