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ortho–para-Directing Activators: –CH3, –OH, –⁠NH2, –OCH301:11

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All ortho–para directors, excluding halogens, are activating groups. These groups donate electrons to the ring, making the ring carbons electron-rich. Consequently, the reactivity of the aromatic ring towards electrophilic substitution increases. For instance, the nitration of anisole is about 10,000 times faster than the nitration of benzene. The electron-donating effect of the methoxy group in anisole activates the ortho and para positions on the ring and stabilizes the corresponding...
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When disubstituted benzenes undergo electrophilic substitution, the product distribution depends on the directing effect of both substituents. When the directing effects of both substituents reinforce each other, a single product is obtained. For example, bromination of p-nitrotoluene occurs ortho to the methyl group and meta to the nitro group, which is the same position, resulting in a single product. However, if the directing effects of the two groups oppose each other, the...
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Directing Effect of Substituents: meta-Directing Groups01:09

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Substituents on the benzene ring that direct an incoming electrophile to undergo substitution at the meta position are called meta directors. All meta directors either have a positive charge on the atom directly bonded to the ring or a partial positive charge. These groups function by withdrawing electrons from the ring through inductive and resonance effects. Consider the carbocation intermediates formed upon the addition of an electrophile on nitrobenzene at the...
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Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule02:17

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If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
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The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.
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ortho–para-Directing Deactivators: Halogens01:24

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Halogens are ortho–para directors. They are more electronegative than carbon. Therefore, as ring substituents, they can withdraw electrons through the inductive effect and deactivate the aromatic ring towards electrophilic substitution. Halogens also have an electron-donating resonance effect on the ring, which influences the orientation of the incoming electrophile. If an electrophile attacks at the ortho or the para position, the halogen donates electrons and stabilizes the intermediate...
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Modulación de la geometría de amida retorcida y la reactividad a través de efectos de sustitución remota

Mizhi Xu, McKinley K Paul, Krista K Bullard

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    Los investigadores modularon la reactividad de la amida retorcida utilizando sustituyentes remotos. Los grupos donantes de electrones aumentaron las tasas de distorsión de amida y sustitución nucleofílica, revelando mecanismos de reacción dependientes del sustituyente.

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    Área de la Ciencia:

    • Química orgánica
    • Mecanismos de reacción
    • Química sintética

    Sus antecedentes:

    • La reactividad de las amidas retorcidas está tradicionalmente vinculada a su distorsión.
    • Las amidas bicíclicas puentes clásicas presentan limitaciones en la modificación de la distorsión de las amidas.
    • Se necesitan nuevas estrategias para afinar la geometría y la reactividad de la amida.

    Objetivo del estudio:

    • Investigar la modulación de la geometría y la reactividad de las amidas retorcidas.
    • Explorar el impacto de los efectos de sustitución remota en un solo andamio de amida.
    • Comprender la cinética y los mecanismos de las amidas retorcidas sustituidas en las reacciones de apertura de anillos.

    Principales métodos:

    • Cálculos computacionales para determinar las geometrías del estado básico.
    • Síntesis divergente para crear una biblioteca de derivados de amida retorcidos.
    • Estudios cinéticos y mecanicistas de la reacción de apertura de anillo de alquilación/rebote de haluro.

    Principales resultados:

    • Los sustituyentes remotos modulan significativamente la geometría y la reactividad de las amidas retorcidas.
    • Los sustituyentes donantes de electrones aumentan la distorsión de los enlaces de amida y las tasas de reacción.
    • Las tasas de reacción de la sustitución nucleofílica abarcan casi dos órdenes de magnitud.
    • El paso de limitación de la tasa depende de la naturaleza del sustituto.

    Conclusiones:

    • Los efectos de sustitución remota ofrecen una herramienta poderosa para controlar las propiedades de las amidas retorcidas.
    • La distorsión de la amida está directamente correlacionada con la fuerza del sustituyente donante de electrones.
    • La vía de reacción y la eficiencia están influenciadas por el sustituto, la polaridad del disolvente y el ion haluro.