Lecture 11 IR Theory Next Class: Lecture Problem 4 due Thin-Layer Chromatography This Week In Lab:...
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Transcript of Lecture 11 IR Theory Next Class: Lecture Problem 4 due Thin-Layer Chromatography This Week In Lab:...
![Page 1: Lecture 11 IR Theory Next Class: Lecture Problem 4 due Thin-Layer Chromatography This Week In Lab: Ch 6: Procedures 2 & 3 Procedure 4 (outside of lab)](https://reader036.fdocuments.in/reader036/viewer/2022062315/5697c0071a28abf838cc6023/html5/thumbnails/1.jpg)
Lecture 11
IR Theory
Next Class:• Lecture Problem 4 due• Thin-Layer Chromatography
This Week In Lab:Ch 6: Procedures 2 & 3 Procedure 4 (outside of lab)
Next Week in Lab:• Ch 7: PreLab Due• Quiz 4• Ch 5 Final Report Due
![Page 2: Lecture 11 IR Theory Next Class: Lecture Problem 4 due Thin-Layer Chromatography This Week In Lab: Ch 6: Procedures 2 & 3 Procedure 4 (outside of lab)](https://reader036.fdocuments.in/reader036/viewer/2022062315/5697c0071a28abf838cc6023/html5/thumbnails/2.jpg)
Spectroscopy
1H NMR:Determine bond connectivities/pieces of a structure, whole structure
IR Use:Determine the functional groups present in a structure:
-OH, C=O, C-O, NH2, C=C, CC, C=N, CN
NMR (Nuclear Magnetic Resonance Spectroscopy):•Uses radio waves (electromagnetic radiation)•Interacts with sample’s nuclei in the presence of a magnet•Effect: nuclei flip and relax (known as resonance)
IR (Infrared Spectroscopy)•IR radiation•Interacts with molecule as a whole•Effect: bond vibrations within molecule
![Page 3: Lecture 11 IR Theory Next Class: Lecture Problem 4 due Thin-Layer Chromatography This Week In Lab: Ch 6: Procedures 2 & 3 Procedure 4 (outside of lab)](https://reader036.fdocuments.in/reader036/viewer/2022062315/5697c0071a28abf838cc6023/html5/thumbnails/3.jpg)
An IR Spectrum of Hexanol
![Page 4: Lecture 11 IR Theory Next Class: Lecture Problem 4 due Thin-Layer Chromatography This Week In Lab: Ch 6: Procedures 2 & 3 Procedure 4 (outside of lab)](https://reader036.fdocuments.in/reader036/viewer/2022062315/5697c0071a28abf838cc6023/html5/thumbnails/4.jpg)
IR Spectroscopy
Main Use: To detect the presence or absence of a functional group (specific bonds) in a molecule
How It Works:1. Bonds vibrate freely at specific wavelengths (wavenumbers)2. Want to cause the bonds to increase the magnitude of this vibrational
frequency3. Subject compound to IR radiation, 4000-625 cm-1
cm-1 is the unit for wavenumber () (The numbers of waves within 1 cm) is directly proportional to energy (unlike wavelength)
4. Bonds absorb energy equal to their natural vibrational energy - it is quantized. This absorption of energy causes a change in dipole moment
for the bond.5. Upon absorption, bonds stretch and/or bend; the IR measures this
absorption.
![Page 5: Lecture 11 IR Theory Next Class: Lecture Problem 4 due Thin-Layer Chromatography This Week In Lab: Ch 6: Procedures 2 & 3 Procedure 4 (outside of lab)](https://reader036.fdocuments.in/reader036/viewer/2022062315/5697c0071a28abf838cc6023/html5/thumbnails/5.jpg)
Vibrational Modes of Bonds
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Correlation Chart Specific bonds absorb specific IR radiation and signals will appear within certainwavenumber ranges (similar to NMR).
Your lab notebook also has an IR correlation chart.
![Page 7: Lecture 11 IR Theory Next Class: Lecture Problem 4 due Thin-Layer Chromatography This Week In Lab: Ch 6: Procedures 2 & 3 Procedure 4 (outside of lab)](https://reader036.fdocuments.in/reader036/viewer/2022062315/5697c0071a28abf838cc6023/html5/thumbnails/7.jpg)
Correlation Chart Specific bonds absorb specific IR radiation and signals will appear within certainwavenumber ranges (similar to NMR).
Correlation of Bond Stretching and IR Absorption (See also Correlation Chart & Table in LabGuide)
Type of Bond Group Family of Compounds Wavenumber Range (cm-1)
Single Bonds —C—H Alkanes 2850-3300
=C—H Alkenes, aromatics 3000-3100
≡ —C H Alkynes 3300-3320
O—H Alcohols 3200-3600
N—H Amines 3300-3500
—C O Ethers, Ester , s AlcoholsCarboxyl icAcids
1330-1000
Doubl e Bonds =C C Alkene, s aromatics 1600-1680
=C O Carbonyls 1680-1750
Aldehyde , s ketones 1710-1750
Carboxyl icacids 1700-1725
Esters, amides 1680-1750
=C N Imines 1500-1650
Trip leBonds C≡C Alkynes 2100-2200
C≡N Nitriles 2200-2300
![Page 8: Lecture 11 IR Theory Next Class: Lecture Problem 4 due Thin-Layer Chromatography This Week In Lab: Ch 6: Procedures 2 & 3 Procedure 4 (outside of lab)](https://reader036.fdocuments.in/reader036/viewer/2022062315/5697c0071a28abf838cc6023/html5/thumbnails/8.jpg)
Functional group region: Fingerprint region:1550-4000 cm-1 400-1550 cm-1
Most useful portion of More diff icult to interpret; mayIR spectrum contain useful informationEvaluate t his portion foryour spectral unknown
IR spectrum of hexanoic acid
OH
O
![Page 9: Lecture 11 IR Theory Next Class: Lecture Problem 4 due Thin-Layer Chromatography This Week In Lab: Ch 6: Procedures 2 & 3 Procedure 4 (outside of lab)](https://reader036.fdocuments.in/reader036/viewer/2022062315/5697c0071a28abf838cc6023/html5/thumbnails/9.jpg)
Different bond stretches & what their signals look like in IR:
A: O-H stretch (strong, broad)C: C-H stretch (strong, sharp)E: CC or CN stretch (sharp)F: C=O stretch (strong, medium to sharp)G: C=C stretch (sharp)J: C-O stretch (strong, medium)K: C-X stretch (sharp)
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Lab Guide Problem 16.1
A sample is known to have the molecular formula C4H10O and to be one of two constitutional isomers, either t-butyl alcohol or isopropyl methylether. What is the structure of the unknown?
QuickTime™ and aTIFF (LZW) decompressor
are needed to see this picture.
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Lab Guide Problem 16.2(a)
Indicate how the following pairs of compounds could be distinguished usingcharacteristic IR peaks:
(a) Benzaldehyde (C6H5O) and benzoic acid (C6H5COOH)
1. Consider each structure:
2. Determine the main differences that would be seen in IR.
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Lab Guide Problem 21.20
An unknown oxygen-containing compound is suspected of being an alcohol,a ketone, or a carboxylic acid. Its IR spectrum shows a broad strong peakat 3100-3400 cm-1 and a strong, sharp peak at 1700 cm-1. What kind ofcompound is it?
Consider what type of bonds appear in the ranges given. Refer to correlation chart.
Broad peak at 3100-3400 cm-1 Strong, sharp peak at 1700 cm-1
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Lab Guide Problem 21.21
A compound with molecular formula C4H8O shows no absorption in the IRregion near 1700 cm-1 or 3400 cm-1. What can you deduce about its structure? Propose one possible structure.
What can you deduce about its structure?
Propose one possible structure.1. Calculate HDI.
2. Give possible structure(s):