Name: hydrogen bonding effects in ir o-h peaks
Uploaded: 2024-12-05T18:32:10.000Z
Duration: 1 min 23 s
Channel: JoVE

Recordemos que la frecuencia vibratoria de un enlace es proporcional a la raíz cuadrada de la constante de fuerza, considerando solo los efectos de la fuerza del enlace y no los factores de masa reducidos.
Por lo tanto, los enlaces más fuertes con constantes de fuerza más altas vibran a frecuencias más altas tras la absorción IR. Los enlaces más débiles vibran a frecuencias más bajas.
Por ejemplo, los enlaces de hidrógeno intermoleculares observados en alcoholes y fenoles debilitan el enlace O-H existente, influyendo así en la posición del pico O-H característico.
En una solución muy diluida o en una fase gaseosa, la ausencia de enlaces H intermoleculares da como resultado un pico agudo a ≈3600 cm-1.
En soluciones concentradas, como las moléculas están involucradas en diversos grados de enlace H, se obtiene una banda muy ancha en el rango de 3200-3550 cm-1.
En soluciones moderadamente diluidas, se observan picos agudos y anchos correspondientes a las vibraciones O-H libres y enlazadas con H, respectivamente.
Además, la presencia de grupos voluminosos impide las interacciones de enlace H, generando solo un pico agudo independientemente del estado físico del alcohol o fenol.

ensanchamiento de picos del espectro ir: enlaces de hidrógeno.

IR Spectrum Peak Broadening: Hydrogen Bonding

La frecuencia vibracional de un enlace es directamente proporcional a su fuerza de enlace. Como resultado, los enlaces más fuertes vibran a frecuencias más altas, mientras que los enlaces más débiles vibran a frecuencias más bajas. La vibración de estiramiento del enlace fuerte O–H en alcoholes y fenoles (solución muy diluida o fase gaseosa) aparece como un pico agudo a 3600–3650 cm-1.

Sin embargo, la extensión del enlace de hidrógeno influye en la frecuencia de estiramiento observada y el ensanchamiento de banda. El enlace de hidrógeno intermolecular o intramolecular debilita el enlace O–H, lo que da como resultado un rango de fuerzas de enlace (3300–3400 cm-1). Por lo tanto, la vibración de estiramiento del O–H unido por hidrógeno en soluciones concentradas aparece como una señal amplia en la espectroscopia IR. En soluciones moderadamente diluidas, la señal aguda del estiramiento del O–H libre aparece junto a la señal amplia del O–H unido por hidrógeno.

Cuando la presencia de grupos voluminosos impide las interacciones de enlace de hidrógeno, se observa una banda nítida independientemente del estado físico del alcohol o del fenol. De manera similar, las moléculas que presentan enlaces de hidrógeno intramoleculares muestran una banda ancha independientemente de la concentración. Por ejemplo, los fenoles sustituidos con ortocarbonilo muestran una señal ancha a 3200 cm-1 en todas las concentraciones.

En los ácidos carboxílicos, los enlaces de hidrógeno intermoleculares entre dos moléculas conducen a la formación de dímeros. La banda O–H aparece como un pico muy ancho (2400–3400 cm-1) centrado en ≈3000 cm-1.

Ensanchamiento de picos del espectro IR: enlaces de hidrógeno.

La frecuencia vibratoria de un enlace es directamente proporcional a su fuerza de enlace. Como resultado, los enlaces más fuertes vibran a frecuencias más altas, mientras que los más débiles ...

ir-spectrum-peak-broadening-hydrogen-bonding

Education

Educación

JoVE Core

Analytical Chemistry

Química Analítica

Unit 1

Unidad 1

Molecular Vibrational Spectroscopy

Espectroscopía vibracional molecular

KEY TERMS AND CONCEPTS

TÉRMINOS Y CONCEPTOS CLAVE

hydrogen bonding effects in ir o-h peaks

Hydrogen bonding changes the O-H stretching peak in IR spectroscopy. The bond’s vibrational frequency depends on bond strength. Stronger bonds vibrate at higher frequencies, while weaker bonds vibrate at lower frequencies.

In very dilute alcohol or phenol samples, or in the gas phase, the strong O-H bond gives a sharp peak at 3600-3650 cm−1. When intermolecular hydrogen bonding or intramolecular hydrogen bonding weakens the O-H bond, the stretch shifts to about 3300-3400 cm−1. This range of bond strengths produces a broad signal in concentrated solutions.

In moderately dilute solutions, both forms can appear. The free O-H stretch gives a sharp signal, and the hydrogen-bonded O-H stretch gives a broad one beside it. If bulky groups block hydrogen bonding, the band stays sharp no matter whether the alcohol or phenol is in a solid, liquid, or gas state.

Molecules with intramolecular hydrogen bonding also show a broad band at all concentrations. Ortho-carbonyl substituted phenols are one example, with a broad signal near 3200 cm−1. Carboxylic acids show an even broader O-H peak because two molecules form hydrogen-bonded dimers. Their band extends from 2400-3400 cm−1 and is centered at about 3000 cm−1.

Hydrogen Bonding Effects in IR O-H Peaks

infrared (ir) spectroscopy: overview

IR Spectra and Functional Group ID

Infrared (IR) spectroscopy helps identify functional groups in molecules by measuring how they absorb infrared light. It is based on the idea that electromagnetic radiation can move atoms or molecules from a lower energy state to a higher one when the radiation matches the energy gap between those states. In IR spectroscopy, that absorption happens as molecular vibrations change.

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IR spectroscopy explains how covalently bonded molecules absorb infrared radiation by moving to higher vibrational levels. The key motions are stretching and bending vibrations. These motions help describe how a bond responds when it absorbs IR energy. Stretching vibrations happen along the bond line and change the distance between two bonded atoms. They can be symmetric, where two bonds lengthen and shorten together, or asymmetric, where one bond moves one way while another moves the opposite...

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Conjugation Shifts IR Bond Stretching

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Triple-Bond Signals in IR Spectra

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IR Signals for C=C and C=O Bonds

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IR Peak Intensity and Bond Dipole Change

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IR Absorption and Bond Dipole Changes

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ir spectrum peak broadening: hydrogen bonding

Hydrogen bonding changes the O-H stretching peak in IR spectroscopy. The bond’s vibrational frequency depends on bond strength. Stronger bonds vibrate at higher frequencies, while weaker bonds vibrate at lower frequencies. In very dilute alcohol or phenol samples, or in the gas phase, the strong O-H bond gives a sharp peak at 3600-3650 cm−1. When intermolecular hydrogen bonding or intramolecular hydrogen bonding weakens the O-H bond, the stretch shifts to about 3300-3400 cm−1. This range of...

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IR Peak Splitting in Amines and Nitro Groups

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key terms and concepts

See how hydrogen bonding shifts and broadens O-H peaks in IR spectra, from sharp free O-H bands to broad signals in alcohols, phenols, and carboxylic acids.

Hydrogen Bonding Effects in IR O-H Peaks | JoVE K12

analytical chemistry

JoVE Core Analytical Chemistry simplifies complex chemical principles by breaking them down into clear, engaging animations, making topics from SI Units to NMR spectroscopy more accessible and straightforward. Additionally, the scientist-in-action videos highlight the application of these concepts in real-world research conducted in laboratories globally.

Hydrogen Bonding Effects in IR O-H Peaks

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