N-TRICHLOROACETYL AND DICHLOROACETYL AMINO-ACIDS AND COMPOUNDS OF AMINO-ACIDS WITH HALOGENO ACETIC-ACIDS - CL-35 NUCLEAR-QUADRUPOLE RESONANCE SPECTROSCOPY - CRYSTAL-STRUCTURE OF N-TRICHLOROACETYL-GLYCINE, N-TRICHLOROACETYL-L-ALANINE, AND N-TRICHLOROACETYL-L-ALANINE

The crystal structures of N-trichloroacetyl-glycine (N-TCA-G), N-trich loroacetyl-DL-alanine (N-TCA-DL-A), and N-trichloroacetyl-L-alanine (N -TCA-L-A) were determined. In addition, the Cl-35 NQR spectra of these N-trichloroacetyl amino acids, of N-trichloroacetyl-L-valine (N-TCA-L -V), and of N-dichloroacetyl-glycine and -L-alanine were measured, mos tly as a function of temperature. Compounds of glycine and L-alanine w ith chlorodifluoroacetic acid, of glycine and L-leucine with monochlor oacetic acid, of glycine and L-leucine with dichloroacetic acid, and o f glycine and L-leucine with trichloroacetic acid were also studied us ing Cl-35 NQR. The structures (in picometres and degrees) were found t o be as follows. N-TCA-G: Pna2(1), Z = 8, a = 1641, b = 1002, c = 1018 . N-TCA-DL-A: C2/c, Z = 8, a = 3280, b = 556, c = 1031, beta = 96.68. N-TCA-L-A: P1, Z = 2, a = 967, b = 949, c = 619, alpha = 74.97, beta = 74.20, gamma = 61.20. The Cl-35 NQR frequencies (upsilon) were observ ed in the range 35-41 MHz, and decrease with increasing temperature. S ome of the resonances bleach out at a temperature (T-b) far below the melting temperature; this provides information about the crystal struc tures at 77 K. No phase transitions were observed by differential ther mal analysis between 77 and 295 K. The crystal structures are discusse d in connection with the NQR results, and conclusions are drawn about the structures of the compounds for which only Cl-35 NQR data are avai lable.