Unlock hundreds more features
Save your Quiz to the Dashboard
View and Export Results
Use AI to Create Quizzes and Analyse Results

OR
Sign inSign in with Facebook
Sign inSign in with Google
Quizzes > Science

IR Spectroscopy Quiz: Identify Peaks and Functional Groups

20 quick questions with instant feedback-IR spectrum practice that builds speed.

Editorial: Review CompletedCreated By: Malaury ConsequenceUpdated Aug 27, 2025
Difficulty: Moderate
Grade: Grade 12
Study OutcomesCheat Sheet
Colorful paper art promoting IR Spectroscopy Challenge, a quiz for AP and college chemistry students.

This IR spectroscopy quiz helps you read spectra, match key peak ranges, and spot common functional groups. Answer 20 quick questions with instant feedback to build speed and confidence before class or lab. For more practice on structures, try our functional groups quiz or push your skills with the identify functional groups quiz.

Which region of the IR spectrum is typically used to identify functional group stretches rather than fingerprint features?
7000 to 4000 cm-1
1500 to 400 cm-1
Below 400 cm-1
4000 to 1500 cm-1
undefined
A sharp, strong absorption near 1715 cm-1 most commonly indicates which functional group in a simple, unconjugated molecule?
Alcohol O-H stretch
Alkyne C≡C stretch
Ketone C=O stretch
Nitrile C≡N stretch
undefined
Statement: A bond must undergo a change in dipole moment during vibration to be IR-active.
True
False
undefined
Which functional group most reliably shows a single, sharp absorption near 2250 cm-1 without an accompanying bending band near ~1400 cm-1?
Nitrile C≡N
Aromatic C-H
Alkene C=C
Isocyanate N=C=O
undefined
Statement: O-H stretching bands of hydrogen-bonded alcohols are typically broad compared to free O-H stretches.
True
False
undefined
Which carbonyl derivative typically absorbs at the highest wavenumber for its C=O stretch?
Ketone
Amide
Acid chloride
Aldehyde
undefined
Which change would you expect when replacing H with D (deuterium) in an O-H bond?
Stretching frequency doubles
Stretching frequency decreases approximately by factor of sqrt(2)
No significant change
Stretching frequency increases by 10 percent
undefined
Statement: Conjugation of a carbonyl with an aromatic ring typically decreases its C=O stretching frequency by about 20 to 30 cm-1 compared to a saturated analog.
True
False
undefined
In an FTIR, co-adding scans primarily improves which aspect of the spectrum?
Wavenumber accuracy increases linearly with scans
Baseline slope is eliminated completely
Spectral resolution doubles with each additional scan
Signal-to-noise ratio improves as the square root of number of scans
undefined
Which band assignment is most consistent with a primary amine?
Broad O-H stretch only
One N-H stretch near 3300 cm-1
Strong band at 2250 cm-1
Two N-H stretches near 3300 to 3500 cm-1
undefined
Which factor increases the ATR depth of penetration for a given wavenumber?
Using a higher refractive index crystal
Shorter wavelength (higher wavenumber) radiation
Higher angle of incidence away from critical angle
Lower refractive index of the sample relative to the crystal
undefined
Statement: In gas-phase IR spectra, vibrational bands can show P and R branches due to rotational structure flanking the band center.
False
True
undefined
A strong doublet of carbonyl bands near 1820 and 1760 cm-1 most likely indicates which functional group?
Ester
Aldehyde
Acid anhydride
Acid chloride
undefined
Which statement about Fermi resonance in IR spectra is most accurate?
It requires isotopic substitution to occur
It arises from interaction between a fundamental and an overtone/combination band of similar energy
It only occurs in Raman spectra, not IR
It eliminates the fundamental band entirely
undefined
Statement: The asymmetric stretch of a nitro group generally appears at lower wavenumber than its symmetric stretch.
False
True
undefined
Statement: Polarization effects are generally negligible in ATR with unpolarized sources, but can matter when using polarized IR for oriented samples.
False
True
undefined
Which processing choice in FTIR most directly affects sidelobe artifacts around sharp bands?
Number of scans
Purge gas flow rate
Detector type
Apodization (window) function
undefined
Which sample characteristic most challenges mid-IR transmission but is often manageable with ATR?
Strongly absorbing, thick or highly scattering solids
Transparent solutions in non-polar solvents
Aqueous solutions at low concentration
Highly volatile gases
undefined
Statement: In a centrosymmetric linear molecule like CO2, the symmetric stretch is IR active while the asymmetric stretch is IR inactive.
False
True
undefined
Which approach best improves quantitative accuracy for ATR measurements across different samples?
Use fewer scans to avoid baseline drift
Use effective pathlength correction using refractive index and penetration depth
Ignore contact pressure variations
Decrease resolution to 8 cm-1
undefined
0

Study Outcomes

  1. Identify characteristic absorption peaks associated with specific molecular vibrations.
  2. Interpret IR spectra to determine functional groups present in organic compounds.
  3. Analyze the relationship between molecular structure and spectral patterns.
  4. Apply infrared spectroscopy principles to solve structural determination problems.
  5. Evaluate experimental IR data to support chemical analysis and hypothesis testing.

IR Spectroscopy Practice Problems Cheat Sheet

  1. IR Spectroscopy Basics - Infrared spectroscopy measures how molecules absorb IR light, causing bonds to vibrate like tiny springs and revealing functional groups by their unique absorption peaks. For example, a carbonyl (C=O) stretch typically appears around 1700 cm−1, making it a signature fingerprint.
  2. Know the IR Regions - The IR spectrum spans near (700 - 2500 nm), mid (2500 - 25 000 nm), and far-infrared (25 000 - 1 000 000 nm), each region tuning into different molecular vibrations and overtones. By selecting the right "radio station," you can focus on fundamental modes or delve into low-frequency motions.
  3. IR‑Active Molecules - Only vibrations that change a molecule's dipole moment appear in an IR spectrum, so symmetric diatomics like O₂ and N₂ remain silent. This selection rule helps you predict which species will show up in your scan and which will stay hidden.
  4. Functional Group vs. Fingerprint Regions - The functional group region (3600 - 1200 cm−1) flags common bonds like OH, NH, and C=O, while the fingerprint region (1200 - 600 cm−1) offers a unique tangle of peaks for each molecule - even isomers. This two-tiered approach lets you match broad patterns and fine details to nail down compound identity.
  5. Band Intensities - A band's intensity depends on how dramatic the dipole moment change is during vibration plus the concentration of absorbing molecules. Think of it like the difference between a whisper and a shout - more molecules and bigger polarity shifts yield bolder peaks.
  6. IR Spectroscopy Limitations - IR can't detect homonuclear diatomics such as N₂ and O₂ because they lack a dipole moment change, and mixtures or aqueous solutions often produce overlapping bands that are hard to resolve. Knowing these blind spots helps you plan sample prep or choose supplementary methods.
  7. Spectrometer Components - An IR spectrometer is built from five parts: an IR source to emit light, a sample holder to position your material, a monochromator or interferometer to separate wavelengths, a detector to record absorption, and software to convert data into spectra. Each component plays a starring role in delivering clear, accurate results.
  8. Qualitative Organic Analysis - By interpreting peaks in both the functional group and fingerprint regions, you can identify unknown organic compounds like a spectral sleuth - spotting alcohols, carbonyls, and more. This makes IR spectroscopy indispensable in organic labs, quality control, and forensic chemistry.
  9. Versatility of IR - From solids and liquids to gases, powders, and polymers, IR spectroscopy tackles a rainbow of sample types with minimal fuss. Its adaptability spans pharmaceuticals, materials science, environmental monitoring, and beyond - one technique for countless applications.
  10. Practice Makes Perfect - Hone your IR skills by analyzing real spectra: note peak positions, shapes, and intensities, then match them to known functional groups. For instance, spotting a broad O - H stretch between 3200 - 3600 cm−1 instantly flags alcohols or phenols in your sample.
Make a Quiz (FREE) Copy & Edit This Quiz Create a Quiz with AI

Science Quizzes

Powered by: Quiz Maker