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https://hdl.handle.net/10316/10718
Título: | The low temperature crystalline and glassy states of methyl -hydroxy-isobutyrate | Autor: | Jarmelo, Susana Maria, Teresa M. R. Leitão, Maria Luísa P. Fausto, Rui |
Data: | 15-Jan-2001 | Editora: | Royal Society of Chemistry | Citação: | Physical Chemistry Chemical Physics. 3 (2001) 387-392 | Resumo: | The low temperature crystalline and glassy phases of methyl -hydroxy-isobutyrate (MHib) were identified and characterized structurally by differential scanning calorimetry, IR and Raman spectroscopy and molecular modeling. Within the temperature range 13–171 K, MHib exists as a glassy state, where individual molecules may assume the two conformational states previously observed for this compound isolated in an argon matrix and in the liquid phase [S. Jarmelo and R. Fausto, J. Mol. Struct., 1999, 509, 193]. At ca. 171 K, devitrification occurs and a crystalline phase may then be formed [T(onset)213 K], the enthalpy of crystallization being ca. 5 kJ mol–1. The crystalline phase was found to exhibit conformational selectivity—in this phase all individual molecules assume a conformation analogous to the most stable conformer found for the isolated molecule and in the liquid (the Syn-syn s-cis conformer, where the H–O–C–C, O–C–CO and OC–O–C dihedrals are ca. 0°). Molecular modeling and Raman data are consistent with a structural unit within the crystal where two MHib molecules form a centrosymmetrical hydrogen bonded dimer. The observed temperature of fusion [Tf(peak)] for the crystal is 240 K. | URI: | https://hdl.handle.net/10316/10718 | ISSN: | 1463-9076 | DOI: | 10.1039/b007722o | Direitos: | openAccess |
Aparece nas coleções: | FCTUC Química - Artigos em Revistas Internacionais |
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The low temperature crystalline.pdf | 175.24 kB | Adobe PDF | Ver/Abrir |
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