NMR Spectroscopy

⚗️ NMR Spectroscopy

Part 1 of 7 — ¹H NMR Basics

1. NMR

nuclei in magnetic field absorb radiofrequency energy

2. Equivalent protons give one signal

Equivalent protons give one signal

3. Number of signals = number of unique proton environments

Number of signals = number of unique proton environments

4. Chemical shift (δ)

position of signal in ppm

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Key Concepts Summary

• NMR: nuclei in magnetic field absorb radiofrequency energy
• Equivalent protons give one signal
• Number of signals = number of unique proton environments
• Chemical shift (δ): position of signal in ppm

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Chemical Shift

Part 2 of 7 — Chemical Shift

1. TMS (tetramethylsilane) = 0 ppm reference

TMS (tetramethylsilane) = 0 ppm reference

2. Alkyl H

0.8-1.5 ppm

3. Allylic/adjacent to C=O

2.0-2.5 ppm

4. Aromatic H

6.5-8.0 ppm; Aldehyde H: 9-10 ppm; Carboxylic acid: 10-12 ppm

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Key Concepts Summary

• TMS (tetramethylsilane) = 0 ppm reference
• Alkyl H: 0.8-1.5 ppm
• Allylic/adjacent to C=O: 2.0-2.5 ppm
• Aromatic H: 6.5-8.0 ppm; Aldehyde H: 9-10 ppm; Carboxylic acid: 10-12 ppm

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Integration & Splitting

Part 3 of 7 — Integration & Splitting

1. Integration

area under peak proportional to number of H's

2. Splitting (n+1 rule)

n equivalent neighbors → n+1 peaks

3. Doublet

1 neighbor; Triplet: 2 neighbors; Quartet: 3 neighbors

4. Coupling constant (J)

distance between split peaks in Hz

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Key Concepts Summary

• Integration: area under peak proportional to number of H's
• Splitting (n+1 rule): n equivalent neighbors → n+1 peaks
• Doublet: 1 neighbor; Triplet: 2 neighbors; Quartet: 3 neighbors
• Coupling constant (J): distance between split peaks in Hz

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¹³C NMR

Part 4 of 7 — ¹³C NMR

1. ¹³C NMR

one signal per unique carbon environment

2. No splitting in broadband-decoupled ¹³C NMR

No splitting in broadband-decoupled ¹³C NMR

3. DEPT

distinguishes CH₃, CH₂, CH, and quaternary C

4. Chemical shifts span 0-220 ppm

Chemical shifts span 0-220 ppm

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Key Concepts Summary

• ¹³C NMR: one signal per unique carbon environment
• No splitting in broadband-decoupled ¹³C NMR
• DEPT: distinguishes CH₃, CH₂, CH, and quaternary C
• Chemical shifts span 0-220 ppm

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Structure Determination

Part 5 of 7 — Structure Determination

1. Step 1

determine molecular formula and degrees of unsaturation

2. Step 2

analyze IR for functional groups

3. Step 3

count ¹H NMR signals, integration, splitting

4. Step 4

assemble fragments into consistent structure

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Key Concepts Summary

• Step 1: determine molecular formula and degrees of unsaturation
• Step 2: analyze IR for functional groups
• Step 3: count ¹H NMR signals, integration, splitting
• Step 4: assemble fragments into consistent structure

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Problem-Solving Workshop

Part 6 of 7 — Problem-Solving Workshop

1. Predicting NMR spectra from structures

Predicting NMR spectra from structures

2. Determining structures from NMR data

Determining structures from NMR data

3. Combining IR, MS, and NMR data

Combining IR, MS, and NMR data

4. Practice problems with unknown identification

Practice problems with unknown identification

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Key Concepts Summary

• Predicting NMR spectra from structures
• Determining structures from NMR data
• Combining IR, MS, and NMR data
• Practice problems with unknown identification

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Synthesis & Review

Part 7 of 7 — Synthesis & Review

1. NMR is the most powerful structural tool

NMR is the most powerful structural tool

2. Chemical shift indicates electronic environment

Chemical shift indicates electronic environment

3. Splitting pattern reveals connectivity

Splitting pattern reveals connectivity

4. Review

systematic structure determination

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Key Concepts Summary

• NMR is the most powerful structural tool
• Chemical shift indicates electronic environment
• Splitting pattern reveals connectivity
• Review: systematic structure determination

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