How does IR spectroscopy allow identification of different functional groups?

Different functional groups absorb infrared radiation at specific, characteristic wavenumbers, producing distinct peaks in the spectrum that can be matched to known values.

What type of absorption does the C–H bond in alkanes produce in an IR spectrum?

A stretching absorption peak at a characteristic wavenumber range.

Why does C–H stretching in alkenes occur at a different wavenumber range compared to alkanes?

Because the carbon in alkenes is sp² hybridised rather than sp³ hybridised, which affects the bond strength and therefore the absorption frequency.

What is distinctive about the C–H stretching absorption in aldehydes?

It often appears as two peaks due to the characteristic aldehyde C–H stretch.

What type of peak does C=C stretching in alkenes produce in an IR spectrum?

A characteristic absorption peak at a specific wavenumber range.

Edexcel A-Level Chemistry 9CH0

Atomic Structure and the Periodic Table

Topic overview Protons, neutrons, electrons and isotopes Relative atomic mass and the mass spectrum Ionisation energy and the evidence for sub-shells Orbitals and electron configuration Periodicity across a period and down a group

Bonding and Structure

Topic overview Ionic bonding Covalent bonding, dative bonding and the shapes of molecules Electronegativity, polarity and intermolecular forces Structure and properties

Redox I

Topic overview Oxidation numbers Oxidation, reduction, disproportionation and half-equations

Inorganic Chemistry and the Periodic Table

Topic overview Flame tests and how they work Thermal decomposition of nitrates and carbonates Carrying out flame tests and testing the gases Group 2 elements and their compounds Trends in Group 7 and predicting fluorine and astatine Halogen displacement reactions Disproportionation and the reactions of chlorine Halides with concentrated sulfuric acid, and the hydrogen halides Testing for halide ions with silver nitrate Testing for carbonate and hydrogencarbonate ions Testing for sulfate and ammonium ions

Formulae, Equations and Amounts of Substance

Topic overview The mole, molar mass and empirical formula The ideal gas equation and molar volume Equations, concentration and reacting quantities Standard solutions, titration and uncertainty Percentage yield, atom economy and acid reactions Core practicals 1 to 3 Empirical formula and water of crystallisation by experiment Apparatus, uncertainty and mathematical skills

Organic Chemistry I

Topic overview Formulae, homologous series and functional groups IUPAC nomenclature Types of organic reaction and structural isomerism Stereoisomerism and E/Z nomenclature Practical techniques in organic chemistry Alkanes, crude oil and combustion pollutants Radical substitution Alkenes, the double bond and hydrogenation Electrophilic addition, Markovnikov's rule and the test for an alkene Addition polymers and waste polymers Nucleophilic substitution of halogenoalkanes Rates of hydrolysis and the SN1 and SN2 mechanisms Classifying and oxidising alcohols Alcohols: practical techniques and the core practicals

Modern Analytical Techniques I

Topic overview Mass spectrometry Infrared spectroscopy and the characteristic absorptions Deducing functional groups from an infrared spectrum

Energetics I

Topic overview Enthalpy changes, standard definitions and calorimetry Hess's law and bond enthalpies

Kinetics I

Topic overview Collision theory and factors affecting rate Maxwell-Boltzmann distribution and temperature Catalysts, reaction profiles and measuring rate

Equilibrium I

Topic overview Dynamic equilibrium and Le Chatelier's principle The equilibrium constant Kc

Equilibrium II

Topic overview Partial pressures and Kp Calculating Kp and the effect of conditions

Acid-Base Equilibria

Topic overview Bronsted-Lowry acids and bases, and the pH scale Strong and weak acids, Ka and Kw Calculating pH, and titration curves Buffer solutions and the Henderson-Hasselbalch equation Buffers in blood, and the core practical

Energetics II

Topic overview Lattice energy Born-Haber cycles and electron affinity Entropy and the direction of change Gibbs free energy and thermodynamic feasibility

Redox II

Topic overview Standard electrode potentials and the hydrogen electrode Electrochemical cells, emf and cell diagrams Feasibility, the electrochemical series and disproportionation Storage cells, fuel cells and redox titrations

Transition Metals

Topic overview Electron configuration and what makes a transition metal Complex ions, ligands and the colour of transition metal ions Coordination number, monodentate ligands and the shapes of complexes Bidentate and multidentate ligands, and ligand exchange Vanadium and chromium chemistry Reactions with sodium hydroxide and ammonia Cobalt and copper complexes Ligand exchange, amphoteric behaviour and the chelate effect Transition metals as catalysts

Kinetics II

Topic overview Rate equations, orders and the rate constant Determining orders from experiments Rate-determining step and mechanisms Arrhenius equation and activation energy

Organic Chemistry II

Topic overview Chirality Aldehydes, ketones and their oxidation Reduction and nucleophilic addition of HCN Testing for a carbonyl group: 2,4-DNPH and the iodoform reaction Carboxylic acids and their reactions Esters and acyl chlorides Reflux, extraction and recrystallisation Distillation, melting temperature and working safely

Organic Chemistry III

Topic overview The structure of benzene and the evidence for it Electrophilic substitution of benzene Nitration, halogenation, Friedel-Crafts and phenol Amines: structure and basicity Reactions of amines and preparing them Amides and condensation polymers Amino acids, zwitterions and proteins Empirical and molecular formulae from analytical data Grignard reagents and multi-step synthesis Purification techniques and the aspirin preparation

Modern Analytical Techniques II

Topic overview Carbon-13 and proton NMR Splitting, integration and the reference standard Chromatography High-resolution mass spectrometry

Modern Analytical Techniques I

Infrared spectroscopy and the characteristic absorptions

3 things to know
Papers 2 and 3

Overview

How infrared absorptions at characteristic wavenumbers identify functional groups, the C–H, C=C, O–H, C=O and N–H absorptions, why O–H peaks are broad and broader still in carboxylic acids, and telling primary from secondary amines by their N–H peaks.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Numbers

Which absorptions identify the common functional groups?

Key term

How does the O–H absorption in carboxylic acids differ from that in alcohols?

Key term

What is the purpose of infrared spectroscopy in organic chemistry?

Questions from this subtopic

Each one with the model answer underneath.

1
What is the purpose of infrared spectroscopy in organic chemistry?
Model answer
To spot functional groups, by matching absorptions to the wavenumbers each group is known to appear at.
2
How does IR spectroscopy allow identification of different functional groups?
Model answer
Different functional groups absorb infrared radiation at specific, characteristic wavenumbers, producing distinct peaks in the spectrum that can be matched to known values.
3
What type of absorption does the C–H bond in alkanes produce in an IR spectrum?
Model answer
A stretching absorption peak at a characteristic wavenumber range.
4
Why does C–H stretching in alkenes occur at a different wavenumber range compared to alkanes?
Model answer
Because the carbon in alkenes is sp² hybridised rather than sp³ hybridised, which affects the bond strength and therefore the absorption frequency.
5
What is distinctive about the C–H stretching absorption in aldehydes?
Model answer
It often appears as two peaks due to the characteristic aldehyde C–H stretch.
6
What type of peak does C=C stretching in alkenes produce in an IR spectrum?
Model answer
A characteristic absorption peak at a specific wavenumber range.

See the rest and revise

Other ways to work this

The same content, four other ways.

What is inside Levo

Six ways to work the same material.

1Closed book

2Open book

3Closed book

The 3-step method, run for you

Answer cold, learn it, then prove it stuck. Levo tracks the jump between your first attempt and your last.

Atomic Structure and the Periodic Table

Bonding and Structure

Redox I

Inorganic Chemistry and the Periodic Table

Cram a whole paper in one sitting

Sort every topic into what you know and what you do not, then drill only the weak ones.

The value .

decreasesincreasesdoubles

Blank Blitz makes facts automatic

Rapid timed gap-fills on the terms and numbers you need to recall without thinking.

AAtomisation turns each element into gaseous atoms.

BIonisation energy removes electrons from the metal atoms.

CElectron affinity adds electrons to the non-metal atoms.

Build It gets the exam shape right

Assemble a full-mark answer from its marking points, in the order an examiner wants them.

Anode means electrode where oxidation occurs.

TrueFalse

Test It catches misconceptions

Spot the fault in a statement. The traps are the mistakes students actually make.

721941163128510

Brain Breaks between sessions

Short focus games to reset attention, so the next set lands better than the last.

Every question in Modern Analytical Techniques I, on a schedule.

Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.

Start revising, £5 a month See how the method works

Or £46 a year, about £3.83 a month. Cancel anytime.