IR & Mass Spectrometry

⚗️ Infrared Mass Spectrometry

Part 1 of 7 — Introduction to Spectroscopy

1. Spectroscopy

using electromagnetic radiation to determine structure

2. Four main techniques

IR, MS, ¹H NMR, ¹³C NMR

3. Each gives different structural information

Each gives different structural information

4. Combined data reveals complete molecular structure

Combined data reveals complete molecular structure

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Key Concepts Summary

• Spectroscopy: using electromagnetic radiation to determine structure
• Four main techniques: IR, MS, ¹H NMR, ¹³C NMR
• Each gives different structural information
• Combined data reveals complete molecular structure

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Infrared (IR) Spectroscopy

Part 2 of 7 — Infrared (IR) Spectroscopy

1. IR measures bond vibrations (stretching and bending)

IR measures bond vibrations (stretching and bending)

2. Frequency measured in wavenumbers (cm⁻¹)

Frequency measured in wavenumbers (cm⁻¹)

3. Fingerprint region

below 1500 cm⁻¹ (complex, unique)

4. Diagnostic region

above 1500 cm⁻¹ (functional groups)

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Key Concepts Summary

• IR measures bond vibrations (stretching and bending)
• Frequency measured in wavenumbers (cm⁻¹)
• Fingerprint region: below 1500 cm⁻¹ (complex, unique)
• Diagnostic region: above 1500 cm⁻¹ (functional groups)

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Key IR Absorptions

Part 3 of 7 — Key IR Absorptions

1. O-H (alcohol)

3200-3600 cm⁻¹ (broad)

2. N-H (amine)

3300-3500 cm⁻¹

3. C=O (carbonyl)

1680-1750 cm⁻¹ (strong, sharp)

4. C≡C (alkyne)

~2150 cm⁻¹; C≡N (nitrile): ~2250 cm⁻¹

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Key Concepts Summary

• O-H (alcohol): 3200-3600 cm⁻¹ (broad)
• N-H (amine): 3300-3500 cm⁻¹
• C=O (carbonyl): 1680-1750 cm⁻¹ (strong, sharp)
• C≡C (alkyne): ~2150 cm⁻¹; C≡N (nitrile): ~2250 cm⁻¹

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Mass Spectrometry

Part 4 of 7 — Mass Spectrometry

1. Mass spectrometry

measures mass-to-charge ratio (m/z)

2. Molecular ion peak (M⁺)

gives molecular weight

3. M+1 peak

¹³C isotope

4. M+2 peak

Cl (35/37) or Br (79/81) isotope pattern

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Key Concepts Summary

• Mass spectrometry: measures mass-to-charge ratio (m/z)
• Molecular ion peak (M⁺): gives molecular weight
• M+1 peak: ¹³C isotope
• M+2 peak: Cl (35/37) or Br (79/81) isotope pattern

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Fragmentation Patterns

Part 5 of 7 — Fragmentation Patterns

1. Base peak

most abundant fragment

2. Common losses

-15 (CH₃), -18 (H₂O), -28 (CO), -29 (CHO)

3. McLafferty rearrangement

γ-hydrogen transfer

4. Nitrogen rule

odd molecular weight suggests nitrogen

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Key Concepts Summary

• Base peak: most abundant fragment
• Common losses: -15 (CH₃), -18 (H₂O), -28 (CO), -29 (CHO)
• McLafferty rearrangement: γ-hydrogen transfer
• Nitrogen rule: odd molecular weight suggests nitrogen

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Problem-Solving Workshop

Part 6 of 7 — Problem-Solving Workshop

1. Interpreting IR spectra to identify functional groups

Interpreting IR spectra to identify functional groups

2. Analyzing mass spectra for molecular weight and fragments

Analyzing mass spectra for molecular weight and fragments

3. Combining IR and MS data

Combining IR and MS data

4. Practice with unknown identification

Practice with unknown identification

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Key Concepts Summary

• Interpreting IR spectra to identify functional groups
• Analyzing mass spectra for molecular weight and fragments
• Combining IR and MS data
• Practice with unknown identification

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Synthesis & Review

Part 7 of 7 — Synthesis & Review

1. Spectroscopy is essential for structure determination

Spectroscopy is essential for structure determination

2. IR identifies functional groups

IR identifies functional groups

3. MS gives molecular weight and formula clues

MS gives molecular weight and formula clues

4. Review

interpreting spectra systematically

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Key Concepts Summary

• Spectroscopy is essential for structure determination
• IR identifies functional groups
• MS gives molecular weight and formula clues
• Review: interpreting spectra systematically

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