4.5.1 Infrared (IR) spectroscopy

• IR vibrations are classified into two main types: stretching and bending.

  True
• Bending vibrations involve changes in the bond angle between three atoms.angle
• At what point does the sample absorb IR radiation in an IR spectrometer?

  When frequencies match vibrations
• Match the component of an IR spectrometer with its function:

  Infrared source ↔️ Provides infrared radiation

  Detector ↔️ Measures radiation passing through

  Sample ↔️ Absorbs radiation at specific frequencies
• What does the computer/display in an IR spectrometer produce?

  IR spectrum
• What property of functional groups allows IR spectroscopy to identify them?

  Characteristic IR absorption bands
• Steps involved in generating an IR spectrum:

  1️⃣ IR radiation passes through the monochromator

  2️⃣ Specific wavelength shines on the sample

  3️⃣ Detector measures absorbed radiation

  4️⃣ IR spectrum is displayed on the computer
• Alkynes have a characteristic IR absorption peak at approximately 3300 cm^-1.3300
• IR absorption frequencies depend on bond strengths and atomic masses in functional groups.


  True
• The IR absorption range for alkanes is 2850-3000
• Steps in interpreting an IR spectrum:

  1️⃣ Identify major absorption bands

  2️⃣ Correlate bands to functional groups

  3️⃣ Consider intensity and shape
• Carbonyl groups (C=O) in ketones and aldehydes show a sharp, strong peak in the range of 1680-1750
• What is the primary use of IR spectroscopy in organic chemistry?

  Identify functional groups
• The specific frequencies of molecular vibrations depend on bond strength and atomic masses.


  True
• What are the two types of vibrations observed in IR spectroscopy?

  Stretching and bending
• The strength of chemical bonds and atomic masses influence the frequencies of molecular vibrations.


  True
• IR spectroscopy uses infrared radiation to study the vibrational properties of molecules.vibrational
• What does stretching refer to in IR spectroscopy?

  Changes in bond length
• The frequencies of IR vibrations depend on bond strength and atomic masses.


  True
• The IR spectrum is a graph showing the absorbance versus frequency.absorbance
• The monochromator in an IR spectrometer selects a specific wavelength of IR radiation.


  True
• Stretching vibrations involve changes in the bond length between two atoms.length
• The IR source in an IR spectrometer generates a broad range of infrared radiation.


  True
• What is the typical IR absorption range for alkanes?

  2850-3000 cm^-1
• Match the functional group with its IR absorption range:

  Alcohols ↔️ 3200-3600 cm^-1

  Aldehydes ↔️ 2700-2900, 1720-1740 cm^-1

  Carboxylic Acids ↔️ 2500-3300, 1680-1760 cm^-1
• What are the characteristic features of IR absorption peaks for different functional groups?

  Frequencies and ranges
• IR spectroscopy can be used to identify functional groups based on their specific absorption frequencies.


  True
• What are the key steps in interpreting an IR spectrum?

  Identify major peaks, correlate bands, consider intensity
• What are the typical IR absorption characteristics of O-H groups in alcohols?

  Broad, strong peak
• An IR spectrum with peaks at 3300 cm⁻¹ and 1720 cm⁻¹ indicates the presence of both an alcohol and a carbonyl group.

  True
• Two main types of molecular vibrations in IR spectroscopy are stretching and bending
• Match the functional group with its IR absorption range:

  Alkenes ↔️ 3020-3100 cm^-1

  Carboxylic Acids ↔️ 2500-3300, 1680-1760 cm^-1

  Esters ↔️ 1730-1750 cm^-1

  Amines ↔️ 3300-3500 cm^-1
• The IR absorption range for alkynes is 3300
• What type of radiation is used in IR spectroscopy?

  Infrared radiation
• Main components of an IR spectrometer:

  1️⃣ IR source

  2️⃣ Monochromator

  3️⃣ Sample compartment

  4️⃣ Detector

  5️⃣ Computer/Display
• What is the function of the IR source in an IR spectrometer?

  Generates infrared radiation
• Functional groups in organic molecules absorb IR radiation at unique frequencies due to bond vibrations

  True
• Match the functional group with its typical IR absorption range:

  Alcohols (O-H) ↔️ 3200-3600 cm⁻¹

  Ketones (C=O) ↔️ 1680-1750 cm⁻¹

  Amines (N-H) ↔️ 3300-3500 cm⁻¹
• The first step in interpreting an IR spectrum is to identify major absorption bands
• Broader IR absorption peaks may suggest hydrogen bonding or overlapping absorption bands


  True