Jolanta Holband

Variable-temperature crystal structure studies of m-­nitroaniline

The crystal structure of m-nitroaniline has been examined at several temperatures over the 90–350 K range. Thermal evolution of the lattice parameters reveals a weak anomaly at 110 K and an important one at 300 K. The thermal expansion coefficients have been calculated at several temperatures and the principal axes cross-sections of the tensor were drawn. The lattice contraction along the b axis direction has been observed. The rigid-body analysis including an attached rigid group has provided the values of the translation and libration tensors at temperatures studied. The results indicate that m-nitroaniline undergoes a glass transition around 130 K arising from freezing molecular librations and translations. From above 340 K the growing plasticity of the m-nitroaniline crystal results in the loss of X-ray diffraction reflections. This is probably a second-order phase transition. It is coupled with a considerable increase in the nitro group torsion amplitude, but the NH⋯O hydrogen bonds are preserved. Analysis of the temperature evolution of short intermolecular distances enabled us to consider the occurrence of reorienting aggregates of hydrogen-bonded molecules in the high-temperature plastic phase.

Stereochemistry of terpene derivatives. Part 2: Synthesis of new chiral amino acids with potential neuroactivity

Abstract The syntheses and stereochemistry of two new amino acids obtained from the monoterpene ketones (−)- cis -caran- trans -4-one and (−)-menthone via appropriate lactams are presented. The configuration of all stereogenic centers is confirmed by X-ray crystallography.

Reactions of N‐phthalylamino acid chlorides with trialkyl phosphites

Reaction of commercially available trialkyl phosphites with N-phthalylamino acids gave mixtures of seven products, whereas the same reaction carried out with pure triethyl phosphite yielded only the desired 2-(N-phthalytamino)-1-oxoalkanephosphonates. These compounds underwent rearrangement to the same types of products that were obtained with the commercial phosphites. This latter series of reactions was promoted by the presence of dialkyl phosphites.

Conformational polymorphism of diethyl 1-(phthalylglycyloxy)-2-phthalylaminoethenephosphonate

In course of the synthesis of phosphonic derivatives of bestatine, several products have been obtained. One of them turned out to occur in two polymorphic forms. Two crystal structures correspond to two molecular conformations. The crystal structures are as follows: (1a) C24H21N2O9P, P2(1)/n, a = 8.023(2) Angstrom, b = 12.092(2) Angstrom, c = 24.103(5) Angstrom, beta = 92.39(3)degrees, Z = 4, (1b) C24H21N2O9P, P2(1)/c, a = 8.322(1) Angstrom, b = 16.378(2) Angstrom, c = 18.442(2) Angstrom, beta = 101.13(1)degrees, Z = 4. The main conformational difference consists in the mutual orientation of two phthalyl rings. The conformation and packing of sterically overcrowded and conformationally flexible molecules seem to be stabilized by very weak C-H...O hydrogen bonds. The extremely large thermal vibration amplitudes of the phosphonic groups atoms indicate the occurrence of disorder, probably of dynamical character. This disorder becomes frozen below room temperature. The differential scanning calorimetry (DSC) revealed the occurrence of phase transitions below room temperature in both crystals

Variable Temperature Crystal Structure Studies of m-Nitroaniline

The crystal structure of m-nitroaniline has been examined at several temperatures over the 90-350 K range. Thermal evolution of the lattice parameters reveals a weak anomaly at 110 K and an important one at 300 K. The thermal expansion coefficients have been calculated at several temperatures and the principal axes cross-sections of the tensor were drawn. The lattice contraction along the b axis direction has been observed. The rigid-body analysis including an attached rigid group has provided the values of the translation and libration tensors at temperatures studied. The results indicate that m-nitroaniline undergoes a glass transition around 130 K arising from freezing molecular librations and translations. From above 340 K the growing plasticity of the m-nitroaniline crystal results in the loss of X-ray diffraction reflections. This is probably a second-order phase transition. It is coupled with a considerable increase in the nitro group torsion amplitude, but the NH.O hydrogen bonds are preserved. Analysis of the temperature evolution of short intermolecular distances enabled us to consider the occurrence of reorienting aggregates of hydrogen-bonded molecules in the high-temperature plastic phase.