Understanding NMR

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

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

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

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

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

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

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

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

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

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

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

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

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.

1Structure - Models of the Particulate of Matter

1.1Introduction to the Particulate Model of Matter

1.1.1States of Matter

1.1.2Kinetic Molecular Theory

1.1.3Simple Sphere

1.1.4Changing State

1.1.5Forces Between Particles

1.1.6Changes of State

1.1.7Predicting States

1.1.8Changing State HyperLearning

1.1.9Ionization Energy

1.2The Nuclear Atom

1.2.1Fundamental Particles

1.2.2Isotopes & Mass Number

1.2.3Mass Spectrometry

1.2.4Mass Spectrometry

1.2.5Mass Spectroscopy - Analysis

1.2.6Extended Response - Mass Spectrometry

1.2.7Radioactivity

1.3Electron Configuration

1.3.1Electron Shells, Sub-Shells & Orbitals

1.3.2Electron Configuration

1.3.3Absorption & Emission Spectra

1.3.4IB Multiple Choice - Atomic Structure

1.3.5Extended Response - The Atom & Electrons

1.4Counting Particles by Mass: The Mole

1.4.1Relative Masses

1.4.2The Mole

1.4.3IB Multiple Choice - Moles

1.5Ideal Gases

1.5.1Ideal Gas Equation

1.5.2Gas Laws

1.5.3IB Multiple Choice - Gases & Kinetics

1.6Elements, Compounds & Mixtures

1.6.1Fundamental Particles

1.6.2Pure Substances

1.6.3Purity & The Law of Definite Proportion

1.6.4Mixtures

1.6.5Separating Mixtures

1.6.6IB Multiple Choice - Pure Substances

1.6.7Extended Response - Moles & Pure Substances

1.7States of Matter & Changes of State

1.7.1States of Matter

1.7.2Particle Diagrams

1.7.3IB Multiple Choice - Solids, Liquids, & Gases

1.7.4Balancing Equations & Ionic Equations

1.7.5Empirical & Molecular Formulas

1.8Reacting Masses &. Volumes

1.8.1Balancing Equations & Ionic Equations

1.8.2Percentage Yield

1.9Solutions

1.9.1Molarity

1.9.2Particulate Model of Solutions

2Structure - Models of Bonding & Structure

2.1The Ionic Model

2.1.1Ionic Bonding

2.2The Covalent Model

2.2.1Covalent Bonds

2.2.2Complex Ions

2.2.3Factors Affecting Covalent Bond Strength

2.2.4Polarity

2.3Covalent Structures

2.3.1Ionic Lewis Structures

2.3.2Covalent Lewis Structures

2.3.3VSEPR Theory

2.3.4Resonance Structures

2.3.5Allotropes of Carbon

2.3.6Formal Charge

2.3.7End of Topic Quiz - Bonding

2.3.8IB Multiple Choice - Bonding & Lewis Structures

2.3.9IB Multiple Choice - Resonance & Formal Charge

2.4The Metallic Model

2.4.1Metallic Bonding

2.5From Models to Materials

2.5.1Alloys

2.5.2Properties of Polymers

2.5.3Polymerisation Reactions

2.5.4Introduction to Alkenes

2.5.5Reactions of Alkenes

2.5.6End of Topic Quiz - Alkenes

2.6Valence Electrons & Ionic Compounds

2.6.1Valence Electrons & Forming Ions

2.6.2Ionic Compounds

2.6.3End of Topic Quiz - Atoms & Ions

2.6.4IB Multiple Choice - Valence & Ions

2.7Molecular Shape

2.7.1VSEPR

2.7.2Molecular Shapes

2.7.3Bond Hybridization

2.7.4IB Multiple Choice - VSEPR & Bond Hybridization

2.7.5Extended Response - Bonding & Molecular Shape

2.8Intermolecular Forces

2.8.1Introduction to Intermolecular Forces

2.8.2London Dispersion Forces

2.8.3Dipole-Dipole Interactions

2.8.4Ion-Dipole Interactions

2.8.5Hydrogen Bonding

2.8.6Large Biomolecules

2.8.7IB Multiple Choice - Intermolecular Forces

2.8.8Extended Response - Hydrogen Bonding

3Structure - Classification of Matter

3.1The Periodic Table: Classification of Elements

3.1.1The Periodic Table

3.1.2Trends in the Periodic Table

3.1.3End of Topic Quiz - Periodicity & Trends

3.1.4Periodic Trends - Electronegativity & Affinity

3.1.5End of Topic Quiz - Periodic Trends

3.1.6IB Multiple Choice - Periodic Trends

3.1.7Extended Response - Periodic Table

3.2Periodic Trends

3.2.1Atomic & Ionic Radii

3.2.2Ionisation & Electronegativity

3.2.3Metallic Behaviour & Oxides

3.2.4Period 3 Elements & Oxides

3.2.5Period 3 Oxides

3.2.6End of Topic Quiz - Period 3

3.2.7Periodic Trends: Blocks

3.2.8Redox Chemistry

3.3Group 1 Alkali Metals

3.3.1Alkali Metals

3.4Halogens

3.4.1Introduction to Halogens

3.4.2Reactions of Halogens

3.4.3Chlorine & Chlorate(I)

3.4.4End of Topic Quiz - Group 7

3.4.5Exam-Style Question - Group 7

3.4.6End of Topic Quiz - Periodicity, Group 2 & 7

3.5Noble gases, group 18

3.5.1Noble Gases

3.6Functional Groups: Classification of Organic

3.6.1Nomenclature

3.6.2Trends in Physical Properties

3.6.3Saturated & Unsaturated Hydrocarbons

3.6.4Nomenclature contd.

3.6.5Types of Formulas

3.6.6Isomerism

3.6.7Formulae

3.6.8Homologous Series

3.6.9Structural Isomers

3.7Functional Group Chemistry

3.7.1Degrees of Substitution

3.7.2Arenes

3.8Alkanes

3.8.1Alkanes

3.8.2Fractional Distillation

3.8.3Cracking

3.8.4Combustion

3.8.5Chlorination

3.8.6End of Topic Quiz - Alkanes

3.9Alcohols

3.9.1Production of Alcohols

3.9.2Oxidation of Alcohols

3.9.3Oxidation of Alcohols - 2

3.9.4Elimination Reactions

3.9.5End of Topic Quiz - Alcohols

3.9.6Exam-Style Question - Alcohols

3.10Halogenoalkanes

3.10.1Substitution Reactions

3.10.2Elimination Reactions

3.10.3Ozone Depletion

3.10.4End of Topic Quiz - Halogenoalkanes

4Reactivity - What Drives Chemical Reaction?

4.1Endothermic & Exothermic Reactions

4.1.1Endothermic & Exothermic Reactions

4.1.2Energy Diagrams

4.1.3Heat Transfer & Thermal Equilibrium

4.1.4IB Multiple Choice - Enthalpy & Energy

4.2Enthalpy of Reaction, Formation, & Hess' Law

4.2.1Enthalpy of Reaction

4.2.2Bond Enthalpies

4.2.3Enthalpy of Formation

4.2.4Hess’ Law

4.2.5Thermodynamics & Kinetic Control

4.2.6End of Topic Quiz - Thermodynamics

4.2.7IB Multiple Choice - Enthalpy

4.2.8Extended Response - Enthalpy Change

4.3Entropy

4.3.1Introduction to Entropy

4.3.2Absolute Entropy & Entropy Change

4.3.3Free Energy

4.3.4Thermodynamically Favorable Reactions

4.3.5IB Multiple Choice - Entropy & Free Energy

4.3.6Extended Response - Free Energy

5Reactivity - How Much, How Fast & How Far?

5.1Kinetics

5.1.1Collision Theory & Rates of Reaction

5.1.2Maxwell-Boltzmann Distribution

5.1.3Increasing Rates

5.1.4End of Topic Quiz - Kinetics

5.2Rates of Reaction

5.2.1Rate Equations

5.2.2Rate Equations 2

5.2.3The Effect of a Catalyst

5.3Stoichometry

5.3.1Stoichiometry

5.4Le Châtelier’s Principle

5.4.1Introduction to Le Châtelier’s Principle

5.4.2Reaction Quotient & Le Châtelier’s Principle

5.4.3Temperature & Le Châtelier’s Principle

5.4.4IB Multiple Choice -Le Châtelier’s Principle

5.4.5Extended Response - Le Châtelier

5.5Introduction to Equilibrium

5.5.1Equilibrium & Equilibrium Graphs

5.5.2Dynamic Equilibria

5.5.3Reversible Reactions & Directions

5.6Equilibrium Constant

5.6.1Calculating the Equilibrium Constant

5.6.2Magnitude of the Equilibrium Constant

5.6.3Properties of the Equilibrium Constant

5.6.4Calculating Equilibrium Concentrations

5.6.5Representations of Equilibrium

5.6.6IB Multiple Choice - Equilibrium Constants

5.6.7Extended Response - Calculating Kc

5.7Reaction Quotient & Equilibrium Constant

5.7.1Reaction Quotient

5.7.2Equilibrium Constants

5.7.3Partial Pressures

5.7.4Kp

5.7.5IB Multiple Choice - Reaction Quotient & Kp

5.7.6Extended Response - Kp & Bond Enthalpy

6Reactivity - The Mechanisms of Chemical Change

6.1Proton Transfer Reactions

6.1.1Brønsted-Lowry Theory

6.2The pH Scale

6.2.1pH & pOH

6.2.2Ionic Product of Water

6.2.3Using Kw

6.2.4IB Multiple Choice - pH & Kw

6.2.5Extended Response - Kw

6.3Strong & Weak Acids and Bases

6.3.1Strong Acids & Bases

6.3.2Weak Acids & Ka

6.3.3Weak Bases & Kb

6.3.4Weak Acids & Bases Calculation Walkthrough

6.4Acid Deposition

6.4.1Acid Deposition

6.5Types of Organic Reactions

6.5.1Electrophilic Substitution

6.6Oxidation & Reduction

6.6.1Oxidation Number Method

6.6.2Winkler Method

6.6.3Redox Reactions

6.6.4Oxidation States & Equations

6.6.5End of Topic Quiz - Redox

6.6.6Extended Response - Redox Reactions

6.7Electrochemical Cells

6.7.1Introduction to Electrochemical Cells

6.7.2Galvanic Cells

6.7.3Cell Notation

6.7.4Electrolytic Cells

6.7.5Extended Response - Voltaic Cells & Redox

6.8Titration

6.8.1Redox Titrations

6.8.2Titration Calculations

6.8.3Atom Economy

6.9Acid-Base Titrations

6.9.1Titration Calculation Weak Acid & Strong Base

6.9.2Titration Experimental Detail

6.9.3Extended Response - Titration

6.9.4Titration Calculations

6.9.5Titration Curves

6.9.6Titration Calculation Strong Acid & Weak Base

6.9.7IB Multiple Choice - Titrations

6.9.8Polyprotic Acids

6.9.9Titration Calculations Strong Acid & Strong Base

6.9.10Titrations Curves 2

7Measurement, Data Processing & Analysis

7.1Uncertainties & Errors in Measurements & Results

7.1.1Qualitative & Quantitative data

7.2Graphical Techniques

7.2.1Drawing & Interpreting Graphs

7.2.2Linear Interpolation

7.3Spectroscopic Identification of Organic Compounds

7.3.1Understanding NMR

7.3.2Carbon-13 NMR

7.3.3Hydrogen-1 NMR

7.3.4Hydrogen-1 NMR 2

7.3.5End of Topic Quiz - NMR

7.4Infrared Spectroscpy

7.4.1Infrared Spectroscopy

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