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Basicity of Aliphatic Amines

Basicity of Aliphatic Amines

Amines can behave as Brønsted–Lowry bases by accepting a proton from the acid to form corresponding conjugate acids. Due to a lone pair of nonbonding electrons, aliphatic amines can also act as Lewis bases by forming a covalent bond with an electrophile.
To measure the basicity of amines, two conventions are generally used. The first defines Kb as the basicity constant for the deprotonation reaction of water by the amine, as presented in Figure 1. Conventionally, lower Kb indicates higher...

Amides to Carboxylic Acids: Hydrolysis

Amides to Carboxylic Acids: Hydrolysis

Amides can undergo either acid-catalyzed hydrolysis or base-promoted hydrolysis through a typical nucleophilic acyl substitution. Each hydrolysis requires severe conditions.
Acid-catalyzed hydrolysis:
Hydrolysis of amides under acidic conditions yields carboxylic acids. Since the reaction occurs slowly, hydrolysis requires the conditions of heat.
The mechanism begins with the protonation of the carbonyl oxygen by the acid catalyst. The protonation makes the amide carbonyl carbon more...

Preparation of Amides

Preparation of Amides

Amides are synthesized by treating carboxylic acids with amines in the presence of dehydrating agents like dicyclohexylcarbodiimide (DCC).
The DCC-promoted synthesis of amides begins with the protonation of DCC by carboxylic acid. The protonation makes it a better acceptor. Next, the addition of carboxylate to the protonated carbodiimide gives a reactive acylating agent.
Subsequently, the amine acts as a nucleophile that attacks the acylating agent to form a tetrahedral intermediate. In the...

Ions as Acids and Bases

Ions as Acids and Bases

Salts with Acidic Ions
Salts are ionic compounds composed of cations and anions, either of which may be capable of undergoing an acid or base ionization reaction with water. Aqueous salt solutions, therefore, may be acidic, basic, or neutral, depending on the relative acid-base strengths of the salt’s constituent ions. For example, dissolving the ammonium chloride in water results in its dissociation, as described by the equation:

Amines to Amides: Acylation of Amines

Amines to Amides: Acylation of Amines

Various carboxylic acid derivatives (such as acid chlorides, esters, and anhydrides) can be used for the acylation of amines to yield amides. The reaction requires two equivalents of amines. The first amine molecule functions as a nucleophile and attacks the carbonyl carbon to produce a tetrahedral intermediate. This is followed by the loss of the leaving group and restoration of the C=O bond.
Next, the second equivalent of amine serves as a Brønsted base and deprotonates the quaternary amide...

Basicity of Heterocyclic Aromatic Amines

Basicity of Heterocyclic Aromatic Amines

Heterocyclic amines, where the N atom is a part of an alicyclic system, are similar in basicity to alkylamines. Interestingly, the heterocyclic amine having a nitrogen atom as part of an aromatic ring has much less basicity than its corresponding alicyclic counterpart. For this reason, as presented in Figure 1, piperidine (pKb = 2.8) is significantly more basic than pyridine (pKb = 8.8).

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Los cationes se unen sólo débilmente a las amidas en soluciones acuosas.

Halil I Okur¹, Jaibir Kherb, Paul S Cremer

¹Department of Chemistry, Texas A&M University , College Station, Texas 77843, United States.

Journal of the American Chemical Society

|March 23, 2013

Resumen

Los cationes metálicos interactúan débilmente con los grupos amídicos, imitando las interacciones de la columna vertebral de las proteínas. La fuerza de unión catiónica sigue una serie de Hofmeister, con Ca2+) mostrando la interacción más fuerte pero aún con constantes de unión débiles.

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Área de la Ciencia:

Química biofísica y bioquímica.
La espectroscopia es una técnica de espectroscopia.
Física Química Física Química es la física de la química.

Sus antecedentes:

La comprensión de las interacciones de la columna vertebral catión-proteína es crucial para los procesos biológicos.
La butiramida sirve como un compuesto modelo para estudiar estas interacciones en soluciones acuosas.

Objetivo del estudio:

Para investigar las interacciones de la sal con la butiramida como una imitación de las interacciones de cationes con la columna vertebral de la proteína.
Para determinar la fuerza de unión y el orden de los cationes metálicos con grupos amídicos.

Principales métodos:

Espectroscopia de infrarrojos con transformación de Fourier de reflexión total atenuada (ATR-FTIR) para monitorear los desplazamientos de la banda de amida I en soluciones a granel.
Espectroscopia de frecuencia de suma vibratoria (VSFS) para estudiar las interacciones catión-amida en la interfaz aire/agua.

Principales resultados:

Los cationes metálicos bien hidratados (Ca(2+), Mg(2+), Li(+)) indujeron desplazamientos en la banda de amida I, lo que indica una unión catión-amida.
La unión catiónica condujo al ordenamiento de capas de agua adyacentes en la interfaz.
El ordenamiento de cationes observado siguió una serie de Hofmeister: Ca(2+) > Mg(2+) > Li(+) > Na(+) ≈ K(+).
Las constantes de disociación de equilibrio aparente eran débiles, con Ca2+ mostrando la unión más fuerte (~8,5 M).

Conclusiones:

Las interacciones de cationes con amidas son significativamente más débiles que las de aniones débilmente hidratados.
El estudio proporciona evidencia directa de una serie catiónica de Hofmeister en las interacciones catión-amida.