[Author © Dr Phil Brown PhD: Doc Brown's advanced level organic chemistry exam revision notes suitable for students of UK A level chemistry courses & US K12 grade 11, grade 12 and AP honors chemistry courses: Molecular spectrometry - analysing the infrared spectra of cyclohexene [spectra page updated April 3rd 2026 *]

 email doc brown Re-edit infrared spectrum of cyclo-C₆H₁₀

 Infrared spectroscopy - spectra index

Students and teachers please note my explanation of the infrared spectrum of cyclohexene is designed for advanced, but pre-university, chemistry courses.

Based in the infrared spectrum diagram for cyclohexene, only some of the most prominent peaks for particular bond vibrations are discussed, particularly if cyclohexene has a functional group with a particular characteristic wavenumber peak.

The infrared spectrum of cyclohexene is unique and the whole, or selected wavenumbers, can be used to fingerprint its identity, sometimes analysing a mixture containing cyclohexene or following its change of concentration in a reaction.

aliphatic cyclohexene , ,  , 

Key points about the infrared spectrum of cyclohexene

The IR spectrum of cyclohexene shows a C=C stretch near 1650 cm⁻¹, alkene C–H stretch just above 3000 cm⁻¹, strong sp³ C–H stretches below 3000 cm⁻¹, and C–H bending around 1450–1500 cm⁻¹.

These peaks distinguish cyclohexene (an alkene) from cyclohexane (an alkane).

Key Features of Cyclohexene IR Spectrum

• Alkene C–H stretch (~3020–3100 cm⁻¹): Diagnostic of sp² C–H bonds.
• Alkane C–H stretch (~2850–2960 cm⁻¹): Strong, common in saturated hydrocarbons.
• C=C stretch (~1640–1660 cm⁻¹): Medium intensity, hallmark of alkenes.
• C–H bending (~1450 cm⁻¹): Typical alkyl bending vibration.
• Out-of-plane =C–H bending (~650–1000 cm⁻¹): Fingerprint region, diagnostic for alkene substitution pattern.

Table of Prominent Wavenumbers for the infrared spectrum of cyclohexene

Sources: NIST IR spectrum of cyclohexene, StudyGuides blog on cyclohexene IR peaks, StudySeamlessly IR guide.

Common Student Misconceptions

• Confusing alkene C–H with alkane C–H: Students often miss the subtle difference between sp² (>3000 cm⁻¹) and sp³ (<3000 cm⁻¹).
• Expecting a strong C=C peak: The C=C stretch is medium intensity, not as strong as C=O.
• Ignoring out-of-plane bending: Many overlook the fingerprint region, which is crucial for alkene substitution identification.
• Mixing up cyclohexene with cyclohexane: Cyclohexane lacks the >3000 cm⁻¹ alkene C–H and the ~1650 cm⁻¹ C=C stretch.

Exam Revision Tips

• Always check above and below 3000 cm⁻¹: Alkene C–H (>3000) versus alkane C–H (<3000).
• Look for the C=C stretch (~1650 cm⁻¹): Key diagnostic peak for alkenes.
• Use the fingerprint region (650–1000 cm⁻¹): Out-of-plane bending patterns distinguish mono-, di-, or tri-substituted alkenes.
• Compare with cyclohexane spectrum: Cyclohexane shows only sp³ C–H stretches and lacks the alkene signals.
• Exam technique: When asked to identify functional groups, state both the wavenumber and the bond (e.g., “Peak at ~1650 cm⁻¹ corresponds to C=C stretch, confirming alkene”).
• Cross-board consistency: All exam boards (AQA, Edexcel, OCR, WJEC, CCEA, CIE, IB, AP) expect recognition of alkene diagnostic peaks and differentiation from alkanes.

Final comments

For A level and AP exams, focus on:

• C=C stretch (~1650 cm⁻¹).
• Alkene C–H stretch (>3000 cm⁻¹).
• Absence of strong C=O peak (~1700 cm⁻¹).
• Fingerprint region bending (650–1000 cm⁻¹).

These features together confirm cyclohexene’s identity as a cyclic alkene.

The mass spectrum of cyclohexene

The H-1 NMR spectrum of cyclohexene

Website content © Dr Phil Brown 2000+. All copyrights reserved on revision notes, images, quizzes, worksheets etc. Copying of Doc Brown's pre-university advanced level chemistry website material is NOT permitted. Exam revision summaries & references to science course specifications are unofficial. These organic chemistry revision notes on spectroscopy (infrared spectrum of cyclohexene) are suitable for use of pre-university students studying AQA advanced level chemistry, Edexcel advanced level chemistry, OCR advanced level chemistry, IB advanced level chemistry, WJEC (Eduqas) advanced level chemistry, CIE advanced level chemistry, CCEA advanced level chemistry, US grade 11-12 AP honors chemistry courses and they will also prove useful to 1st year undergraduate students of chemistry.