Video Experimental Relacionado
Updated: Jul 15, 2026
09:45
Modification and Functionalization of the Guanidine Group by Tailor-made Precursors
Published on: April 27, 2017
Basicidad de un carbeno estable, el 1,3-di-tert-butilimidazol-2-ilideno, en THF
Yeong-Joon Kim1, Andrew Streitwieser
1Department of Chemistry, University of California, Berkeley, California 94720-1460, USA.
Journal of the American Chemical Society
|May 16, 2002
Resumen
La basicidad del 1,3-di-tert-butilimidazol-2-ilideno se cuantificó utilizando indicadores de hidrocarburos en THF. Este carbeno N-heterocíclico es significativamente más básico en DMSO debido a los posibles efectos de enlace de hidrógeno.
Área de la Ciencia:
- Química orgánica es la química orgánica.
- Química Física es la química física.
Sus antecedentes:
- Los carbenos N-heterocíclicos (NHC) son ligandos importantes en la química organometálica y en la organocatálisis.
- La medición precisa de la basicidad NHC es crucial para predecir su reactividad y estabilidad.
Objetivo del estudio:
- Para determinar la basicidad del 1,3-di-tert-butilimidazol-2-ilideno (1) en el tetrahidrofurano (THF).
- Para investigar el comportamiento de los pares de iones y los iones libres en solución.
- Para explorar la influencia del disolvente en la basicidad del NHC.
Principales métodos:
- Mediciones de basicidad utilizando tres indicadores de hidrocarburos en THF.
- Determinación de la constante de equilibrio para pares de iones y iones libres.
- Análisis espectroscópico en THF y sulfóxido de dimetilo (DMSO).
- Modelado computacional Ab initio. modelado computacional desde el principio.
Principales resultados:
- La basicidad del 1,3-di-tert-butilimidazol-2-ilideno se midió con éxito en THF.
- Se observaron tanto pares de iones como iones libres, con sus respectivas constantes de equilibrio determinadas.
- La homoconjugación no se detectó ni en THF ni en DMSO.
- El carbeno exhibió una basicidad significativamente mayor en DMSO en comparación con el THF, atribuida al enlace de hidrógeno.
Conclusiones:
- El 1,3-di-tert-butilimidazol-2-ilideno demuestra una basicidad sintonizable influenciada por los efectos del disolvente.
- El enlace de hidrógeno juega un papel crítico en la mejora de la basicidad de los NHC protonados en disolventes protóticos polares como el DMSO.
- Los resultados computacionales apoyan los hallazgos experimentales con respecto a la basicidad y las interacciones del disolvente.
Videos de Conceptos Relacionados
01:16Structure of Conjugated Dienes
Introduction
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...
01:24π Molecular Orbitals of 1,3-Butadiene
Conjugated dienes have lower heats of hydrogenation than cumulated and isolated dienes, making them more stable. The enhanced stabilization of conjugated systems can be understood from their π molecular orbitals.
The simplest conjugated diene is 1,3-butadiene: a four-carbon system where each carbon is sp2-hybridized and has an unhybridized p orbital that contains an unpaired electron. According to molecular orbital theory, atomic orbitals combine to form molecular orbitals such that the number...
The simplest conjugated diene is 1,3-butadiene: a four-carbon system where each carbon is sp2-hybridized and has an unhybridized p orbital that contains an unpaired electron. According to molecular orbital theory, atomic orbitals combine to form molecular orbitals such that the number...
01:17Electrophilic 1,2- and 1,4-Addition of HX to 1,3-Butadiene
The electrophilic addition of hydrogen halides such as HBr to alkenes and nonconjugated dienes gives a single product as per Markovnikov’s rule.
01:23Electrophilic Addition of HX to 1,3-Butadiene: Thermodynamic vs Kinetic Control
The addition of a hydrogen halide to 1,3-butadiene gives a mixture of 1,2- and 1,4-adducts. Since more substituted alkenes are more stable, the 1,4-adduct is expected to be the major product. However, the product distribution is strongly influenced by temperature; low temperature favors the 1,2-adduct, whereas the 1,4-adduct is predominant at high temperature.
01:28Stability of Conjugated Dienes
Introduction
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.
A comparison of the enthalpies of hydrogenation of dienes reveals that conjugated dienes release less heat on hydrogenation, rendering them more stable than their nonconjugated analogs.
01:14Electrophilic 1,2- and 1,4-Addition of X2 to 1,3-Butadiene
Electrophilic addition of halogens to alkenes proceeds via a cyclic halonium ion to form a 1,2-dihalide or a vicinal dihalide.