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8.E: Reacciones de Sustitución Nucleofílica (Ejercicios)

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    P8.1: Clasificar las siguientes moléculas en orden de la rapidez con la que se esperaría que reaccionaran\(CH_3SNa\) en acetona. (\(CH_3SNa\)es simplemente la sal sódica de\(CH_3S^-\). \(Na^+\)es un ion espectador.)

    clipboard_e2eb680e307ca6ebc10c23cceb4357719.png

    P8.2: Dibujar estructuras lineales que representan el catión más estable con la fórmula molecular dada:

    1. \(C_3H_7^+\)
    2. \(C_4H_9^+\)
    3. \(C_3H_8N^+\)
    4. \(C_4H_7^+\)

    P8.3: For each pair of carbocations below, choose the one that is more stable, and explain your reasoning.

    clipboard_e3f7686e8ec8963e274685ac6b76ab43c.png

    P8.4: Organizar las siguientes especies en orden de aumentar la nucleofilia en disolvente prótico:

    clipboard_e6b6ab48722b1a58f55ca655b88eaf174.png

    P8.5: Predecir los productos orgánicos de las siguientes reacciones de sustitución nucleofílica, todas las cuales se llevan a cabo en disolvente aprótico polar. Mostrar estereoquímica en carbonos quirales. Consejos:\(Na_2CO_3\), sodium carbonate, is a weak base. For part (f): What is the conjugate acid of \(NH_2^-\)? What is the \(pK_a\) of this conjugate acid, and what is the \(pK_a\) of a terminal alkyne?

    a.

    clipboard_ee740e647f405feabab35d66e08174c2c.png

    b.

    clipboard_e22fd1ecb0d7a4473a180da0c7de2648f.png

    c.

    clipboard_ec977816c7257ca95607bf80f5adff833.png

    d.

    clipboard_e34e3a22559bffce13aea355389df43ca.png

    e.

    clipboard_ebbef5f72f3252ae23fae99247194af1c.png

    f.

    clipboard_ee8af282a146d18d3f662ffee9dfc1b30.png

    P8.6: Which of the reactions in the previous problem has a unimolecular rate determining step? Explain.

    P8.7: From the following pairs, select the compound that would react more rapidly with bromomethane in acetone solvent.

    1. water or hydroxide ion
    2. \(CH_3S^-\) or \(CH_3OH\)
    3. \(CH_2S^-\) or \(CH_3SH\)
    4. acetate ion or hydroxide ion
    5. diethyl sulfide or diethyl ether
    6. dimethylamine or diethylether
    7. trimethylamine or 2,2-dimethylpropane

    P8.8: Methyl iodide (0.10 mole) is added to a solution that contains 0.10 mole \(NaOCH_3\) and 0.10 mole \(NaSCH_3\).

    1. Predict the most abundant neutral organic product that would form, and explain your reasoning.
    2. Assume that you isolate a mixture the major product (which you predicted in part) along with a smaller amount of a different nucleophilic substitution product. Explain briefly but specifically how you could use \(^1H-NMR\) to determine the ratio of the two products in the mixture.

    P8.9: For each pair of compounds, predict which will more rapidly undergo solvolysis in methanol solution.

    clipboard_e248d9c4111c868ea73956af0ff3253d6.png

    P8.10: Predict the solvolysis product(s) of each of the reactions below. Consider both regiochemistry and stereochemistry.

    a.

    clipboard_e4261aad313041f8dc2951c447c122506.png

    b.

    clipboard_e170a7028c9876c068cd3c92dc1e24a38.png

    c.

    clipboard_e93d1d5df68cb405cecfbc1ab043dde05.png

    d. Draw a complete curved-arrow mechanism for the formation of the secondary allylilc alcohol product in part (a).

    P8.11: Show starting compounds that would lead to the following products through nucleophilic substitution reactions.

    a.

    clipboard_e5a5b7bcf499ba51310e147a7122a38b8.png

    b.

    clipboard_ecc6c076f2be68152023429b559726c0b.png

    c.

    clipboard_ea7b21e47e9f93607066a7040e3168769.png

    d.

    clipboard_e1eeafd8e7f4c14d1851f84939bca7f0e.png

    P8.12: The fused ring compound shown below is very unreactive to nucleophilic substitution, even with a powerful nucleophile.. Explain. (Hint – consider bond geometry - a model will be very helpful!)

    clipboard_e62542e3710b4f6cae6ab944c3be9c599.png

    P8.13: La síntesis de laboratorio del difosfato de isopentenilo, la molécula de “bloque de construcción” utilizada por la naturaleza para la construcción de moléculas de isoprenoides (sección 1.3A), se logró convirtiendo primero el alcohol isopentenílico en un tosilato de alquilo y luego desplazando el grupo tosilato con un inorgánico nucleófilo de pirofosfato. Con base en esta descripción verbal, dibujar un mecanismo para el segundo paso (sustitución nucleofílica), mostrando los compuestos de inicio y finalización para el paso y flechas curvas para el movimiento de electrones.

    clipboard_eedcc84c6f84e3b731f0bfbfcaaf83769.png

    P8.14: La colina, un importante neutotransmisor en el sistema nervioso, se forma a partir de 2- (N, N-dimetilamino) etanol:

    clipboard_e3de417a0ee9fbd8ea883ba45b45ad006.png

    1. Además de la enzima y el compuesto de partida, ¿qué otra biomolécula importante esperas que desempeñe un papel en la reacción?
    2. Dibuja un mecanismo para la reacción.
    3. Explique brevemente cómo se\(^1H-NMR\) podría utilizar para distinguir entre el sustrato y el producto de esta reacción.

    P8.15: La siguiente es una reacción en la biosíntesis de morfina en amapolas de opio. (Ciencia 1967, 155, 170; J. Biol. Chem 1995, 270, 31091).

    clipboard_edda6acc286154e9eebc18347070b57dd.png

    1. Dibuje un mecanismo completo, asumiendo un\(S_N1\) pathway.
    2. What would you expect to be the most noticeable difference between the IR spectrum of the product and that of the substrate?
    3. This reaction is an example of the regiospecificity of enzymatic nucleophilic substitution reactions noted earlier in the chapter. Draw two alternate nucleophilic, ring-closing steps for this reaction (leading to different products from what is shown above), and explain why these alternate pathways are both less favorable than the actual reaction catalyzed by the enzyme.

    P8.16: The enzymatic reaction below, which is part of the metabolism of nucleic acids, proceeds by an \(S_N1\) mechanism. The new bond formed in the substitution is indicated.

    1. Predict the structures of the two substrates A and B.
    2. Draw a complete mechanism, and use resonance drawings to illustrate how both the carbocation intermediate and the leaving group are stabilized.

    clipboard_e80b40a81bf2e2dd8f216f95d676fbb26.png

    P8.17: Below is the first step of the reaction catalyzed by anthranilate synthase, an enzyme involved in biosynthesis of the amino acid tryptophan.

    1. This reaction is somewhat unusual in that the leaving group is a hydroxide anion, which is of course is normally thought to be a very poor leaving group. However, studies show that an \(Mg^{+2}\) ion is bound in the active site close to the hydroxide. Explain how the presence of the magnesium ion contributes to the viability of hydroxide as a leaving group.
    2. Draw a complete mechanism for the reaction, assuming an \(S_N1\) pathway.

    clipboard_e996dcbd0a35e922046a987882065d810.png

    P8.18: The reaction below is part of the biosynthesis of peptidoglycan, a major component of bacterial cell walls. Is it likely to proceed by a nucleophilic substitution mechanism? Explain.

    clipboard_eb5528d8605efb47412defb71d0f3608a.png

    P8.19: Comparar la reacción a continuación, catalizada por la enzima AMP-DMAPP transferasa, con la reacción de la proteína preniltransferasa que aprendimos en la sección 8.8, cuyo mecanismo, como discutimos, se piensa que es mayormente\(S_N2\) similar con algún carácter\(S_N1\) similar.

    1. ¿Es probable que la reacción de AMP-DMAPP transferasa a continuación tenga un carácter más o menos\(S_N1\) similar en comparación con la reacción de la proteína preniltransferasa? Explique.

    clipboard_e85af79a77bb4723f686499234b81d417.png

    1. Dada su respuesta a la parte (a), ¿qué reacción es probable que se ralentice más drásticamente cuando un análogo de sustrato de isoprenoide fluorado es sustituido por el sustrato natural? Explique.

    clipboard_ee1e365de20e2a3f689978ac39fde1d69.png

    P8.20: En un experimento clásico en química física orgánica, (\(R\))-2-iodooctane was allowed to react (non-enzymatically) with a radioactive isotope of iodide ion, and the researchers monitored how fast the radioactive iodide was incorporated into the alkane (the rate constant of incorporation, \(k_i\)) and also how fast optical activity was lost (the rate constant of racemization, \(k_r\)). They found that the rate of racemization was, within experimental error, equal to twice the rate of incorporation. Discuss the significance of this result - what does it say about the actual mechanism of the reaction?

    This page titled 8.E: Reacciones de Sustitución Nucleofílica (Ejercicios) is shared under a CC BY-NC-SA 4.0 license and was authored, remixed, and/or curated by Tim Soderberg via source content that was edited to the style and standards of the LibreTexts platform.