6.7.2 Infrared (IR) Spectroscopy

• What is the purpose of infrared (IR) spectroscopy?

  Identify functional groups
• In IR spectroscopy, bonds can vibrate through stretching, which involves changes in their length
• Stronger bonds vibrate at higher frequencies in IR spectroscopy.
• What does the variable ν represent in the IR spectroscopy formula?

  Vibration frequency
• Match the functional group with its approximate absorption range in IR spectroscopy:

  O-H ↔️ 3200-3600 cm⁻¹

  C=O ↔️ 1650-1750 cm⁻¹

  C-H ↔️ 2850-3000 cm⁻¹

  C-O ↔️ 1000-1300 cm⁻¹
• What causes the absorption of IR radiation in IR spectroscopy?

  Vibrational modes
• Order the two main vibrational modes of bonds in molecules:

  1️⃣ Stretching

  2️⃣ Bending
• IR spectroscopy provides information to identify functional groups
• IR spectroscopy provides detailed structural information like NMR.

  False
• What type of radiation source is used in an IR spectrometer?

  Blackbody radiator
• Match the IR spectroscopy technique with its principle:

  Transmission ↔️ Measures IR radiation passing through sample

  Reflectance ↔️ Measures IR radiation reflected from sample

  ATR ↔️ Measures changes in reflected IR radiation
• The resolving power of an IR spectrometer is its ability to distinguish between closely spaced absorption bands
• The resolving power of an IR spectrometer is calculated using the formula $R =$$\frac{\lambda}{\Delta \lambda}$.
• Order the main components of an IR spectrometer:

  1️⃣ Radiation Source

  2️⃣ Sample Chamber

  3️⃣ Monochromator

  4️⃣ Detector

  5️⃣ Recorder
• What are the two types of vibrations caused by IR radiation in covalent bonds?

  Stretching and bending
• Lighter atoms vibrate at higher frequencies
• What does the variable $\mu$ represent in the vibration frequency formula?


  Reduced mass
• Match the functional group with its approximate absorption range (cm⁻¹):

  O-H ↔️ 3200-3600

  N-H ↔️ 3300-3500
• What is the absorption range of the O-H functional group in IR spectroscopy?

  3200-3600 cm⁻¹
• The N-H functional group absorbs IR radiation in the range of 3300-3500 cm⁻¹
• Lighter atoms in a bond vibrate at lower frequencies.

  False
• Infrared (IR) spectroscopy is used to identify functional groups in organic compounds.
• IR radiation causes covalent bonds to vibrate through stretching and bending.
• Match the functional group with its absorption range in IR spectroscopy:

  O-H ↔️ 3200 - 3600 cm⁻¹

  N-H ↔️ 3300 - 3500 cm⁻¹

  C-O ↔️ 1000 - 1300 cm⁻¹

  C=O ↔️ 1650 - 1750 cm⁻¹

  C-H ↔️ 2850 - 3000 cm⁻¹
• The vibration frequency in IR spectroscopy depends on bond strength and atomic masses.
• Stronger bonds vibrate at higher frequencies in IR spectroscopy.
• What does $ν$ represent in the IR spectroscopy formula?


  Vibration frequency
• The force constant in the IR spectroscopy formula is represented by k.
• What is the reduced mass represented by in the IR spectroscopy formula?

  $\mu$
• Different functional groups absorb IR radiation in the same frequency range.

  False
• There are two main types of vibrational modes: stretching and bending.
• In stretching, the length of the bond increases and decreases.
• In bending, the angle between bonds remains constant.

  False
• Match the analytical technique with its principle and information provided:

  IR Spectroscopy ↔️ Absorption of IR radiation by vibrating bonds ||| Identifies functional groups

  NMR Spectroscopy ↔️ Absorption of radio waves by atomic nuclei ||| Provides structural information
• The frequency at which a bond absorbs IR radiation depends on its bond strength and atomic masses.
• What happens when infrared radiation passes through a sample?

  Vibrational modes are excited
• In stretching vibrational modes, the length of the bond changes
• What changes in bending vibrational modes?

  The angle between bonds
• Stronger bonds and lighter atoms result in higher vibrational frequencies in IR spectroscopy.
• The vibration frequency in IR spectroscopy is described by the formula \sqrt{\frac{k}{\mu}}