Los enolos de lactona son estables en la fase gaseosa pero muy inestables en solución
Frantisek Turecek1, Shetty Vivekananda, Martin Sadílek
1Department of Chemistry, Bagley Hall, Box 351700, University of Washington, Seattle, Washington 98195-1700, USA. turecek@chem.washington.edu
Journal of the American Chemical Society
|October 31, 2002
Resumen
Se generaron y caracterizaron los primeros enolos estables de lactona, revelando una estabilidad única en la fase gaseosa y una acidez significativa en la solución. Estos hallazgos explican por qué los enolos de lactona rara vez se detectan en estudios de líquidos.
Área de la Ciencia:
- Química Física es la química física.
- Química orgánica es la química orgánica.
- Química computacional es la química computacional.
Sus antecedentes:
- Los enolos de la lactona, los tautómeros enol de las lactonas, han sido históricamente evasivos y difíciles de detectar.
- Comprender sus propiedades es crucial para comprender la química y la reactividad de la lactona.
Objetivo del estudio:
- Generar y caracterizar el primer enol representativo de lactona, el 2-hidroxioxol-2-eno (C(5)-1).
- Investigar por computación las propiedades ácido-base de los enolos gaseosos y acuosos de la lactona (C(4)-1 a C(6)-1).
- Para dilucidar los factores que contribuyen a la naturaleza esquiva de los enolos de lactona en solución.
Principales métodos:
- Generación y caracterización de la fase gaseosa mediante la espectrometría de masas de neutralización-reionización.
- Ab initio cálculos químicos cuánticos (QCISD(T)/6-311+G(3df,2p)) para las propiedades termodinámicas.
- Cálculo de las propiedades ácido-base tanto en fase gaseosa como en solución acuosa.
Principales resultados:
- El 2-hidroxioxol-2-eno (C(5)-1) se generó con éxito y se demostró que es estable en la fase gaseosa.
- Los enolos de lactona exhiben altas afinidades de protones en la fase gaseosa (933-944 kJ mol-1) y acidez (1401-1458 kJ mol-1).
- En solución acuosa, los enolos de lactona son significativamente más ácidos (15-20 órdenes de magnitud) que sus lactonas progenitoras, con valores de pK (a) que van desde 5.6 hasta 14.5.5.
Conclusiones:
- Los enolos lactónicos son especies estables en la fase gaseosa.
- Su alta acidez y basicidad en disolventes protóticos explican su naturaleza transitorio y la dificultad de detección en solución.
- El estudio proporciona información fundamental sobre la química de los enolos de lactona.
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