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

تذكر أن التردد الاهتزازي للرابطة يتناسب مع الجذر التربيعي لثابت القوة ، مع الأخذ في الاعتبار تأثيرات قوة الرابطة فقط وليس عوامل الكتلة المخفضة.
وبالتالي ، تهتز الروابط الأقوى ذات ثوابت القوة الأعلى عند ترددات أعلى عند امتصاص الأشعة تحت الحمراء. تهتز الروابط الأضعف عند ترددات منخفضة.
على سبيل المثال ، تعمل الرابطة الهيدروجينية بين الجزيئات التي لوحظت في الكحولات والفينولات على إضعاف رابطة O-H الحالية ، مما يؤثر على موضع ذروة O-H المميزة.
في محلول مخفف جدا أو طور غازي ، يؤدي عدم وجود روابط H بين الجزيئات إلى ذروة حادة عند ≈3600 سم −1.
في المحاليل المركزة ، نظرا لأن الجزيئات تشارك بدرجات متفاوتة من الترابط H ، ينتج عنه نطاق عريض جدا في حدود 3200-3550 سم −1.
في المحاليل المخففة بشكل معتدل ، لوحظت كل من القمم الحادة والعريضة المقابلة للاهتزازات الحرة والمرتبطة ب H ، على التوالي.
موريسو ، يمنع وجود مجموعات ضخمة تفاعلات الترابط H ، مما يولد ذروة حادة فقط بغض النظر عن الحالة الفيزيائية للكحول أو الفينول.

توسيع قمم طيف الأشعة تحت الحمراء: الترابط الهيدروجيني.

IR Spectrum Peak Broadening: Hydrogen Bonding

<div style="direction:rtl">
يتناسب تردد الاهتزاز لرابطة ما بشكل مباشر مع قوة الرابطة. ونتيجة لذلك، الروابط الأقوى تهتزعند ترددات أعلى، بينما تهتز الروابط الأضعف عند ترددات أقل. يظهر اهتزاز التمدد للرابطة القوية O–H في الكحولات والفينولات (لمحلول مخفف للغاية أو للطور الغازي) كقمة حادة عند 3600–3650 سم^-1.
ومع ذلك، فإن قوة الرابطة الهيدروجينية يؤثر على تردد التمدد الملحوظ وتوسيع النطاق. تعمل الرابطة الهيدروجينية الداخلية أو الجزيئية على اضعاف الرابطة O–H، مما يؤدي إلى مدى لقوة الرابطة بين (3300–3400 سم^-1). لذا، يظهر اهتزاز تمدد الرابطة الهيدروجينية ب O–H في المحاليل المركزة كإشارة واسعة في التحليل الطيفي بالأشعة تحت الحمراء. في المحاليل المخففة بشكل معتدل، تظهر الإشارة الحادة من تمدد O–H الحر بجانب الإشارة العريضة من O–H المرتبط برابطة هيدروجينية.
عندما يمنع وجود مجموعات فعالة ضخمة تفاعلات الرابطة الهيدروجينية، يظهر نطاق حاد بغض النظر عن الحالة الفيزيائية للكحول أو الفينول. وبالمثل، تُظهر الجزيئات التي تشمل روابط هيدروجينية داخلية نطاق عريض غيرمرتبط بالتركيز. على سبيل المثال، تُظهر الفينولات المستبدلة بالأورثو-كربونيل نطاق عريض عند 3200 سم^-1 في جميع التركيزات.
في الأحماض الكربوكسيلية، تؤدي الرابطة الهيدروجينية الجزيئية بين جزيئين إلى تكوين ثنائيات. يظهر نطاق O–H كقمة عريضة جدًا (2400–3400 سم^-1) مركزها ≈3000 سم^-1.
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يتناسب التردد الاهتزازي للرابطة طرديا مع قوة الرابطة. نتيجة لذلك ، تهتز الروابط الأقوى عند ترددات أعلى ، بينما تهتز أضعف ...

ir-spectrum-peak-broadening-hydrogen-bonding

Education

JoVE Core

Analytical Chemistry

الكيمياء التحليلية

Unit 1

الوحدة الأولى

Molecular Vibrational Spectroscopy

مطيافية الاهتزاز الجزيئي

KEY TERMS AND CONCEPTS

المصطلحات والمفاهيم الرئيسية

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

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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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Triple-Bond Signals in IR Spectra

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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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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

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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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