IR Analysis Flashcards
What information does IR spectroscopy provide?
It identifies functional groups within molecules based on their vibrational frequencies, but not complete molecular structures.
What regions are key in an IR spectrum?
The main regions are:
4000–3000 cm⁻¹ for O-H and N-H stretching
2000–1500 cm⁻¹ for triple bonds (alkynes, nitriles)
Below 1500 cm⁻¹, the fingerprint region.
What causes bonds to vibrate at specific frequencies in IR spectroscopy?
Vibrational frequencies depend on bond strength and the masses of the bonded atoms.
How is the intensity of absorption in IR spectroscopy determined?
Intensity is related to the change in dipole moment during vibration; larger dipole changes lead to stronger absorptions.
Why is the “fingerprint region” important in IR spectra?
The fingerprint region (below 1500 cm⁻¹) contains unique patterns that can help identify specific molecules.
How is sample preparation important for IR analysis?
Proper sample preparation ensures accurate measurements and prevents contamination that could alter the IR spectrum.
Why is calibration important in IR spectroscopy?
Calibration ensures the accuracy of wavenumber measurements, which is crucial for correctly identifying functional groups.
What is required for a molecule to be IR-active?
The molecule must experience a change in dipole moment during vibration to absorb IR radiation.
What is dispersive spectrometer
Similar to UV spectrometer
Sample is located prior to monochromator to avoid radiation losses
What is the significance of the fingerprint region in IR spectroscopy?
The fingerprint region (below 1500 cm⁻¹) is unique to each molecule, allowing for identification even though it’s less useful for identifying functional groups.
How does bond mass and strength affect IR absorption frequency?
Heavier atoms result in lower frequencies, while stronger bonds (like double bonds) absorb at higher frequencies.
What determines the intensity of IR absorption signals?
The intensity is influenced by the dipole moment change during vibration; highly polar bonds like O-H and C=O produce stronger signals.
How are samples commonly prepared for IR analysis?
Using methods like KBr discs, mulls, thin films, or Attenuated Total Reflectance (ATR), which require little or no sample preparation.
Why is calibration important in IR spectroscopy?
Calibration ensures accurate wavenumber measurements, typically done with a polystyrene standard to check key bands for compliance.
How is IR spectroscopy used in pharmaceutical applications?
For drug identification, quality control, and monitoring chemical changes in synthesis (e.g., carboxylic acid to amide conversion).
