On the Order‐Disorder Phase Transition of Anilinium Halides. VI. Phase Transition in 4‐RC6H4NHX⊖, and C6H5NR'HX⊖, X = Br,I. A 79,81 Br and 127I NQR Study

1984

Self Cite

By 79,81 Brand "' I NQR the hydrobromides of glycine, I-alanine, I-leucine, 1-proline, semicarbazide and the hydroiodides of I-leucine and semicarbazide were studied in the temperature range 77 5 T/K < decomposition point. Furthermore the compound diglycine sodium iodide monohydrate was investigated. A phase transition is observed for I-leucine hydrobromide at 331.5 K, which is reversible and of small transition enthalpy, as shown by DTA. -79*8i Br NQR frequencies are strongly influenced by hydrogen bonds N+ -H . . . Br-and 0 -H . . . Br-. The "Br frequencies can be grouped into two bands, one at 15 < v/MHz < 19, the other at 24 < v/MHz < 26. The high frequency group of compounds is characterized by N + -H . . . Br-and 0-H . . . Br-hydrogen bonds, whereas the bond scheme of the low frequency compounds is determined by bonds N+ -H . . . Br-only. This grouping of the amino acid hydrobromides according to frequency band and hydrogen bond scheme can be applied to the hydroiodides and to diglycine sodium iodide monohydrate, too.

Hydrogen Bonds in Hydrohalides of Amino Acids. A ^79,81Br and ¹²⁷I NQR Study

Fleck

1984

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On the Order‐Disorder Phase Transition of Anilinium Halides. ¹²⁷I‐NQR Investigation of the Anilinium Iodides C₆H₅NHI^⊖, C₆H₅NDI^⊖, C₆D₅NHI^⊖, and C₆D₅NDI^⊖. Dilatometric Studies on Anilinium Bromide and Anilinium Iodide Single Crystals

Feeder

1986

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127I‐NQR measurements in the range 77 ≤ T/K ≤ 520 are reported for anilinium iodides C6H5NH⊕3I⊖, C6H5ND⊕3I⊖, C6D5NH⊕3I⊖, and C6D5ND⊕3I⊖. The compound undergoes a ferroelastic phase transition at 240.3 K (C6H5NH⊕3I⊖). The transition temperature changes to 233.6 K (C6H5ND⊕3I⊖) and to 233.4 K (C6D5ND⊕3I⊖) by deuteration. The NQR parameters are thereby influenced too. At 293 K the −NH⊕3 group deuteration influences e2ϕzzQh−1 and η much stronger than the ring deuteration, whereas at 77 K these effects are of comparable magnitude.—The thermal expansion coefficients were measured for C6H5NH⊕3X⊕, X = Br, I, from 120 K to 300 K. by dilatometry and by X‐ray diffraction. In C6H5NH⊕3Br⊖ the three linear expansion coefficients are increasing over the whole temperature range studied, whereas in C6H5NH⊕3I⊖ α[010] increases and both, α[100] and α[001], decrease with increasing temperature. On hand of the known crystal structures the ferroelastic phase transition in the anilinium halides is discussed. The basic mechanism of the transition is the same for C6H5NH⊕3I⊖ and C6H5NH⊕3Br⊖. Freezing in of the −NH⊕3 group hindered rotation is the main process governing the phase transitions, but motions of the phenyl ring are of influence, too.

^79,81Br and ¹²⁷I NQR studies of hydrobromides and hydriodides of amino acids and dipeptides

Kehrer

Fleck

1987

Self Cite

By 79,81Br and 127I NQR the hydrobromides of 1‐asparagine, 1‐asparatic acid, glycyl‐1‐alanine, and glycylglycine and the hydriodides of 1‐asparagine, 1‐glutamic acid, and glycylglycine were studied in the temperature range of 77 ≤ T/K ≤ 420 (or decomposition point). — A reversible phase transition is observed for glycyl‐1‐alanine hydrobromide at 203 ± 1 K. 79,81Br NQR frequencies are strongly influenced by N⊕—H…Br⊖ and O—H…Br⊖ hydrogen bonds. The 79Br frequencies can be grouped into two bands, one at 12.4 < v/MHz < 18.5, the other at 24.8 < v/MHz < 26.4. The compounds of the high frequency group are characterized by N⊕—H…Br⊖ and O—H…Br⊖ hydrogen bonds, whereas the bond scheme of the low frequency compounds is determined by N⊕—H…Br⊖ bonds only. This grouping of amino acid and dipeptide hydrobromides according to frequency band and hydrogen bond scheme can be applied to the hydriodides, too. The ones with a O—H…I⊖ hydrogen bond have nuclear quadrupole coupling constants of N⊕ > 120 MHz, the other compounds with N⊕—H…I⊖ hydrogen bonds only show nuclear quadrupole coupling constants of 70 < e2QzzQh−1/MHz < 120.