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

Ricordiamo che la frequenza vibrazionale di un legame è proporzionale alla radice quadrata della costante di forza, considerando solo gli effetti della forza di legame e non i fattori di massa ridotti.
Pertanto, legami più forti con costanti di forza più elevate vibrano a frequenze più elevate al momento dell'assorbimento IR. I legami più deboli vibrano alle frequenze più basse.
Ad esempio, il legame idrogeno intermolecolare osservato negli alcoli e nei fenoli indebolisce il legame O-H esistente, influenzando così la posizione del caratteristico picco O-H.
In una soluzione molto diluita o in una fase gassosa, l'assenza di legami H intermolecolari provoca un picco acuto a ≈3600 cm−1.
In soluzioni concentrate, poiché le molecole sono coinvolte in vari gradi di legame H, si ottiene una banda molto ampia nell'intervallo 3200-3550 cm-1.
In soluzioni moderatamente diluite, si osservano picchi sia acuti che ampi corrispondenti rispettivamente alle vibrazioni O-H libere e legate ad H.
Inoltre, la presenza di gruppi voluminosi impedisce le interazioni di legame H, generando solo un picco acuto indipendentemente dallo stato fisico dell'alcol o del fenolo.

ampliamento del picco dello spettro ir: legame a idrogeno.

IR Spectrum Peak Broadening: Hydrogen Bonding

La frequenza vibrazionale di un legame è direttamente proporzionale alla sua forza di legame. Di conseguenza, i legami più forti vibrano a frequenze più alte, mentre i legami più deboli vibrano a frequenze più basse. La vibrazione di stiramento del forte legame O–H in alcoli e fenoli (soluzione molto diluita o fase gassosa) appare come un picco netto a 3600–3650 cm^-1.

Tuttavia, l'entità del legame a idrogeno influenza la frequenza di stiramento osservata e l’ampliamento della banda. Il legame a idrogeno intermolecolare o intramolecolare indebolisce il legame O–H, portando a un intervallo di forze di legame (3300–3400 cm^-1). Quindi, la vibrazione di stiramento dell'O–H legato a idrogeno in soluzioni concentrate appare come un segnale ampio nella spettroscopia IR. In soluzioni moderatamente diluite, il segnale netto dello stiramento dell'O–H libero appare accanto al segnale ampio dell'O–H legato a idrogeno.

Quando la presenza di gruppi voluminosi impedisce interazioni dei legame a idrogeno, si osserva una banda netta indipendentemente dallo stato fisico dell'alcol o del fenolo. Analogamente, le molecole che presentano legami a idrogeno intramolecolari mostrano una banda ampia indipendentemente dalla concentrazione. Ad esempio, i fenoli sostituiti con orto-carbonile mostrano un segnale ampio a 3200 cm^-1 a tutte le concentrazioni.

Negli acidi carbossilici, il legame a idrogeno intermolecolare tra due molecole porta alla formazione di dimeri. La banda O–H appare come un picco molto ampio (2400–3400 cm^-1) centrato a ≈3000 cm^-1.

Ampliamento del Picco dello Spettro IR: Legame a Idrogeno.

La frequenza vibrazionale di un legame è direttamente proporzionale alla sua forza di adesione. Di conseguenza, i legami più forti vibrano a frequenze più elevate, mentre i legami più deboli ...

ir-spectrum-peak-broadening-hydrogen-bonding

Education

Didattica

JoVE Core

Analytical Chemistry

Chimica Analitica

Unit 1

Unità 1

Molecular Vibrational Spectroscopy

Spettroscopia vibrazionale molecolare

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

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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Molecular bond vibrations can be modeled with IR spectroscopy using Hooke’s law. A covalently bonded heteronuclear diatomic molecule is treated like two masses connected by a spring. The atoms act like the masses, and the bond acts like the spring. Hooke’s law links the vibrational frequency to two main factors. The frequency increases with the force constant, K, which describes bond stiffness. It decreases with the reduced mass, μ, which combines the masses of both atoms into one value for...

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Conjugation Shifts IR Bond Stretching

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Triple-Bond Signals in IR Spectra

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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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raman spectroscopy: overview

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Raman spectroscopy uses laser light to study how molecules scatter light and reveal their vibrational energy levels. A monochromatic beam, or single-color light, hits the sample first. Most of the scattered light keeps the same frequency as the incoming light. This is called Rayleigh scattering. A small part of the light shifts in frequency because the photons exchange energy with molecular vibrations. That shifted light is Raman scattering. To collect a Raman spectrum, the sample is...

raman spectroscopy instrumentation: overview

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Raman Spectroscopy Setup and Detectors

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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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