3.9.8

Nuclear Magnetic Resonance

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Basic NMR Principles

Nuclear Magnetic Resonance (NMR) spectroscopy is a widely used analytical technique for the characterisation of organic compounds.

Information given by NMR spectra

Information given by NMR spectra

  • An NMR spectrum gives information about the environments and positions of hydrogen and carbon atoms in a molecule.
    • This makes it a very powerful analytical tool for chemists.
Overall spin

Overall spin

  • In NMR, we can only analyse nuclei that have an overall spin.
    • These are nuclei that have an odd nucleon number.
    • The nucleon number is equal to the number of protons + number of neutrons.
  • 13C and 1H are both examples of such nuclei. This is why these isotopes are commonly used for NMR.
    • The nucleon number of 13C is 13.
    • The nucleon number of 1H is 1.
External magnetic field

External magnetic field

  • In NMR spectroscopy, we place a sample substance into a magnetic field.
  • As we've said, the nuclei of the substance have an overall spin.
    • This means that the nuclei are each very small magnetic fields themselves.
    • The nuclei can interact with the externally applied magnetic field that they are sitting in.
  • The overall nuclear spin can either spin with or against the external magnetic field.

NMR Theory

We will now consider what causes the signals produced in NMR spectra. Remember the NMR can either be 1H NMR or 13C NMR.

Nuclei in a magnetic field

Nuclei in a magnetic field

  • The nuclei sit in a magnetic field and some of their overall spins will spin with the magnetic field and some will spin against the field.
  • We call whether they spin with or against the field different spin states.
    • The nuclei spinning with the magnetic field are lower in energy.
    • The nuclei spinning against the magnetic field are higher in energy.
Energy difference

Energy difference

  • The nuclei can exist as either of two spin states which are of different energies.
  • So energy must be gained or lost for a nucleus to change its spin state.
    • We say there is an energy gap between the two spin states.
Energy gap

Energy gap

  • The energy gap between the two spin states corresponds to energy in the radio frequency region.
  • So we use radio waves to change the nuclear spin state of the nuclei.
NMR signals

NMR signals

  • Transitions between nuclear spin states appear as signals in the NMR spectrum.
    • In 1H NMR, the signals represent the 1H nuclei transitioning spin state.
    • In 13C NMR, the signals represent the 13C nuclei transitioning spin state.
Different chemical environments

Different chemical environments

  • The exact energy and frequency of radio waves needed to change the nuclear spin state is different in different chemical environments.
  • So different NMR signals represent nuclei positioned in different chemical environments.
    • In 1H NMR, each signal represents a 1H in a different chemical environment.
    • In 13C NMR, each signal represents a 13C in a different chemical environment.

Chemical Shifts

NMR spectra display signals at specific chemical shift values. The chemical shift is the values that appear on the x-axis of the spectrum.

NMR signals

NMR signals

  • As we've seen, a transition of nuclei between spin states causes a specific signal.
  • Nuclei in the same environment will produce the same signal.
    • For 1H NMR, 1Hs in the same environment produce the same signal.
    • For 13C NMR, 13Cs in the same environment produce the same signal.
Chemical shifts

Chemical shifts

  • A signal appears on the spectrum at a specific point along the x-axis. This is the chemical shift value.
    • Nuclei in the same environment will produce a signal at the same chemical shift value.
  • Overall when we read a spectrum, we can say that each different signal, of a particular chemical shift along the x-axis, represents a nucleus in a different environment.
Chemical shift notation

Chemical shift notation

  • The sign for a chemical shift is δ.
  • The units of chemical shift is ppm.
    • This stands for parts per million.
Chemical shift tables

Chemical shift tables

  • A table of chemical shift values, for both 1H and 13C, has been made.
    • This shows possible chemical shift values for a particular 1H or 13C environment.
    • E.g. A 1H in an alcohol is a specific environment. ROH signals are found between 0.5δppm to 5.0δppm.
Jump to other topics
1

Physical Chemistry

1.1

Atoms, Molecules & Stoichiometry

1.1.1Relative Masses1.1.2The Mole1.1.3Mass Spectrometry1.1.4Empirical & Molecular Formulae1.1.5Balanced Equations1.1.6Molar Volume1.1.7End of Topic Test - Amount of Substance
1.2

Atomic Structure

1.2.1Fundamental Particles1.2.2Isotopes & Mass Number1.2.3Electron Shells, Sub-Shells & Orbitals1.2.4Electron Configuration1.2.5Ionisation Energy1.2.6Factors Affecting Ionisation Energies1.2.7Trends of Ionisation1.2.8Specific Impacts on Ionisation Energies1.2.9Electron Affinity1.2.10End of Topic Test - Atomic Structure1.2.11A-A* (AO2/3) - Atomic Structure
1.3

Chemical Bonding

1.3.1Ionic Bonding1.3.2Covalent & Dative Bonding1.3.3Shapes of Molecules1.3.4Intermolecular Forces1.3.5Intermolecular Forces 21.3.6Electronegativity1.3.7Bond Length, Bond Energy, & Bond Polarity1.3.8Metallic Bonding1.3.9Physical Properties1.3.10End of Topic Test - Bonding1.3.11A-A* (AO2/3) - Bonding
1.4

States of Matter

1.4.1Simple Covalent Molecules1.4.2The Ideal Gas Equation1.4.3States of Matter1.4.4Particle Diagrams1.4.5The Liquid State1.4.6Giant Ionic Lattices1.4.7Giant Metallic Lattices1.4.8Giant Covalent Structures1.4.9Graphene & Fullerene1.4.10Recycling
1.5

Chemical Energetics

1.5.1Calorimetry1.5.2Bond Enthalpies1.5.3Enthalpy Changes1.5.4Hess' Law1.5.5Born-Haber Cycles1.5.6Born-Haber Cycle Calculations1.5.7Entropy1.5.8Free Energy1.5.9End of Topic Test - Energetics
1.6

Electrochemistry

1.6.1Electrochemical Cells1.6.2Electrochemical Series1.6.3Commercial Application1.6.4Nernst Equation1.6.5Redox
1.7

Equilibria

1.7.1Dynamic Equilibrium & Le Chatelier1.7.2Kc1.7.3Kp1.7.4pH1.7.5The Ionic Product of Water1.7.6Weak Acids & Bases1.7.7Introduction to Solubility Equilibria1.7.8Solubility Equilibria Calculations1.7.9Free Energy of Dissolution1.7.10pH and Solubility1.7.11Common-Ion Effect1.7.12End of Topic Test - Kp & Electrochemistry1.7.13A-A* (AO2/3) - Electrochemical Cells
1.8

Partition Coefficient

1.8.1Kpc
1.9

Reaction Kinetics

1.9.1Collision Theory1.9.2Orders, Rate Constants & Equations1.9.3Rate Graphs1.9.4Rate Determining Step1.9.5Maxwell-Boltzmann Distribution1.9.6Catalysts1.9.7Homogeneous Catalysts1.9.8Heterogeneous Catalysts1.9.9End of Topic Test - Kinetics1.9.10End of Topic Test - Rate Equations1.9.11A-A* (AO2/3) - Rate Equations
2

Inorganic Chemistry

2.1

The Periodic Table

2.1.1The Periodic Table2.1.2Trends in the Periodic Table2.1.3End of Topic Test - Periodicity & Trends2.1.4Ceramics2.1.5Period 3 Elements & Oxides2.1.6Period 3 Oxides2.1.7End of Topic Test - Period 3
2.2

Group 2

2.2.1Group 2 Chemistry
2.3

Group 17

2.3.1Introduction to Halogens2.3.2Reactions of Halogens2.3.3Chlorine & Chlorate(I)2.3.4End of Topic Test - Group 172.3.5A-A* (AO2/3) - Periodicity, Group 2 & 17
2.4

Transition Metals

2.4.1General Properties2.4.2Titrations2.4.3Shapes of Complex Ions2.4.4Variable Oxidation States2.4.5Ligands2.4.6Colours of Ions2.4.7Stereoisomerism of Complex Ions2.4.8Cisplatin2.4.9Ligand Substitutions & Kstab2.4.10End of Topic Test - Transition Metals2.4.11A-A* (AO2/3) - Transition Metals
2.5

Nitrogen & Sulfur

2.5.1Nitrogen & Ammonia2.5.2Formulated vs Manure Fertilisers2.5.3Nitrogen Containing Fertilisers2.5.4Fertilizers & Eutrophication2.5.5Common Atmospheric Pollutants & Their Properties2.5.6Catalytic Converters2.5.7Atmospheric Oxides
3

Organic Chemistry & Analysis

3.1

Introduction to Organic Chemistry

3.1.1Naming Conventions3.1.2Mechanism3.1.3Isomerism3.1.4End of Topic Test - Introduction to Organic Chem
3.2

Hydrocarbons

3.2.1Fractional Distillation3.2.2Cracking3.2.3Combustion3.2.4Chlorination3.2.5End of Topic Test - Alkanes3.2.6Introduction to Alkenes3.2.7Reactions of Alkenes3.2.8Polymerisation Reactions3.2.9End of Topic Test - Alkenes3.2.10Arenes3.2.11Evidence for Structure of Arenes3.2.12Reactions of Benzene3.2.13End of Topic Test -Arenes
3.3

Halogen Derivatives

3.3.1Properties of Haloalkanes3.3.2Substitution Reactions of Haloalkanes3.3.3Environmental Impacts of Haloalkanes3.3.4End of Topic Test - Halogenoalkanes
3.4

Hydroxy Compounds

3.4.1Types of Alcohol3.4.2Oxidation 13.4.3Oxidation 23.4.4Elimination3.4.5Acids & Esters3.4.6Acyl Chlorides & Acylation3.4.7Phenols & Their Reactions3.4.8End of Topic Test - Alcohols
3.5

Carbonyl Compounds

3.5.1Carbonyls3.5.2Hydrogen Bonding & Carbonyls3.5.3Aldehydes & Ketones3.5.4Tri-Iodomethane Reaction3.5.5End of Topic Test -Carbonyls
3.6

Carboxylic Acids & Derivatives

3.6.1Properties of Carboxylic Acids3.6.2Esters3.6.3Acyl Chlorides3.6.4End of Topic Test - Carboxylic Acids
3.7

Nitrogen Compounds

3.7.1Nature & Preparation of Amines3.7.2Basicity & Nucleophilicity3.7.3Amides3.7.4Reactions of Amino Acids3.7.5Amino Acids
3.8

Polymerisation

3.8.1Properties of Addition Polymers3.8.2Condensation Polymerisation3.8.3Effects of Side-Chains on Polymers3.8.4Hydrolysis of Ester & Amide Groups3.8.5Proteins3.8.6DNA3.8.7Adhesive & Conducting Polymers3.8.8End of Topic Test - Amines & Proteins
3.9

Analytical Techniques

3.9.1Chromatography3.9.2High-Performance Liquid Chromatography3.9.3Gas Chromatography3.9.4IR Spectroscopy3.9.5Uses of IR Spectroscopy3.9.6Mass Spectrometry3.9.7Mass Spectrometry Analysis3.9.8Nuclear Magnetic Resonance3.9.9Carbon-13 NMR3.9.10Proton NMR I3.9.11Proton NMR II3.9.12End of Topic Test - Analytical Techniques3.9.13A-A* (AO2/3) - Analytical Techniques
3.10

Organic Synthesis

3.10.1Chirality & Drug Synthesis3.10.2Organic Synthesis3.10.3Examples of Synthetic Routes3.10.4End of Topic Test - Organic Synthesis

Practice questions on Nuclear Magnetic Resonance

Can you answer these? Test yourself with free interactive practice on Seneca — used by over 10 million students.

  1. 1
    What is the nucleon number of the isotope of carbon that is used in NMR?Multiple choice
  2. 2
    What does NMR stand for?Fill in the list
  3. 3
    A nuclei in a magnetic field will be:Fill in the list
  4. 4
    The energy gap between two spin states corresponds to energy in which region of the electromagnetic spectrum?Multiple choice
  5. 5
    If a <sup>1</sup>H NMR spectrum has 4 signals, how many different <sup>1</sup>H environments are there in the molecule?Multiple choice
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Mass Spectrometry Analysis

Carbon-13 NMR