Infra-Red (IR) Spectroscopy Flashcards
What does infrared spectroscopy do❔
Measures vibrations of
bonds to identify functional groups
What does ultraviolet spectroscopy do?
Measures electronic
transitions to provide information on the electronic
bonding in the sample
What does Mass Spectrometry (MS) do?
Breaks the molecule into
fragments (destructive) and measures the MW of
fragments to give information to the structure and
functional groups present
What does Nuclear Magnetic Resonance (NMR) do?
Uses electromagnetic fields to measure spinning of nuclei
to identify chemical environments leading to identification of functional groups and structure of the
sample
What is the energy equation?
E = hv
planks constant and velocity
What is the wavelength equation?
ɣ = c/v
speed of light/ velocity
What is a photon?
massless packs of energy
What is detected in the IR region + detail on compression?
Molecular vibrations can be detected in the infrared region.
The covalent bonds between atoms act like springs. If the bond is stretched /
compressed and then released, the atoms vibrate.
Explain the different vibrations and bonding?
Heavier atoms vibrate more slowly.
Frequency decreases with increasing
atomic mass
Stronger bonds are more rigid so
they vibrate faster.
More force needed to stretch /
compress (higher frequency)
What is the difference between an active and inactive vibration?
IR-Active Vibrations:
* The bond must have a dipole
moment.
* The vibration must change the dipole
moment of the molecule
IR-Inactive:
* Symmetrical / has no dipole moment
What are some strengths and limitations to IR spectroscopy?
- Ability to indicate functional groups in the compound
- Highlights the absence of other functional groups that would give
strong absorptions if they were present - Can confirm identity of a compound by comparison with a known
sample - It is non-destructive (sample can be retrieved)
