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An applied magnetic field causes loosely bound π-electrons in organic molecules to circulate, producing a local or induced diamagnetic field over a large spatial volume. As the molecules tumble in solution, the field generated by π-electrons in spherical substituents results in a zero net field. However, the net field generated by π-electrons in non-spherical substituents is not zero. The effect of this induced field depends on the orientation of the molecule with respect to B0, resulting in...

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Nitrous acid, a weak acid, is prepared in situ via the reaction of sodium nitrite with a strong acid under cold conditions. This nitrous acid prepared in situ reacts with primary arylamines to form arenediazonium salts. Such reactions are known as diazotization reactions. As shown in Figure 1, the formation of arenediazonium salts begins with the decomposition of nitrous acid in an acidic solution to give nitrosonium ions.

NMR Spectroscopy Of Amines

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In proton NMR spectroscopy, primary amines and secondary amines showcase their N–H protons as a broad signal in the chemical shift range between δ 0.5 and 5 ppm. The exact position in this range depends on several factors, including sample concentration, hydrogen bonding, and the type of solvent used. Since amine protons undergo fast proton exchange in solution, the protons are labile and therefore do not participate in any splitting with adjacent protons. Thus, the observed peak is broad and...

ortho–para-Directing Activators: –CH3, –OH, –&NoBreak;NH2, –OCH3

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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...

Inductive Effects on Chemical Shift: Overview

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The protons in unsubstituted alkanes are strongly shielded with chemical shifts below 1.8 ppm. Methine, methylene, and methyl protons appear at approximately 1.7, 1.2 and 0.7 ppm, while the proton signal from methane appears at 0.23 ppm. An electronegative substituent, such as chlorine, withdraws the electron density from the protons, increasing their chemical shift. Progressive substitution of the hydrogens in methane by chlorine shifts the proton signals increasingly downfield, to 3.05 ppm in...

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Replacing each alpha-hydrogen in chloroethane by bromine (or a different functional group) yields a pair of enantiomers. Such protons are called prochiral or enantiotopic and are related by a mirror plane. Enantiotopic protons are chemically equivalent in an achiral environment. Because most proton NMR spectra are recorded using achiral solvents, enantiotopic hydrogens yield a single signal.
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La posición del átomo H como factor determinante del patrón en las películas de arenetiol.

Ki-Young Kwon¹, Greg Pawin, Kin L Wong

¹Pierce Hall/Department of Chemistry, University of California-Riverside, Riverside, California 92521, USA.

Journal of the American Chemical Society

|April 1, 2009

Resumen

Este resumen es generado por máquina.

Las moléculas de arenetiol forman patrones específicos en las superficies, impulsados por enlaces de hidrógeno. La optimización de las interacciones intermoleculares en posiciones clave guía el diseño de películas de arenetiol para aplicaciones avanzadas.

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Área de la Ciencia:

Ciencias de la superficie Ciencias de la superficie.
Química de materiales Química de materiales
Química supramolecular de las moléculas.

Sus antecedentes:

Las moléculas de arenetiol son cruciales para las monocapas autoensambladas en superficies metálicas.
Comprender las interacciones intermoleculares es clave para controlar la formación y las propiedades de la película.

Objetivo del estudio:

Investigar el papel de la unión de hidrógeno en el autoensamblaje de derivados de benzenetiol y antracenetiol en Cu{111}.
Establecer un principio general para el diseño de películas de arenetiol basadas en interacciones intermoleculares específicas.

Principales métodos:

La difracción de electrones de baja energía (LEED) y la microscopía de túnel de barrido (STM) se utilizaron para estudiar el ordenamiento molecular.
Se realizaron experimentos de recocido para observar la evolución de los arreglos moleculares.

Principales resultados:

El benzenetiol (BT) en Cu{111) exhibe enlaces de hidrógeno S...H que involucran ortohidrógenos en coberturas bajas.
Los antracenetiolos (metilados) forman filas y patrones, dominados por las interacciones de los hidrógenos aromáticos terminales.
Las posiciones específicas de los átomos de hidrógeno dictan el ordenamiento molecular observado y la formación de la película.

Conclusiones:

La formación de patrones en los arenetiolos se rige por la optimización de las interacciones intermoleculares en una posición específica del átomo de hidrógeno en el areno.
Este principio puede guiar el diseño racional de películas de arenetiol ordenadas con propiedades a medida.