IR Spectroscopy Flashcards
(37 cards)
What arises from molecular vibrations in infrared spectroscopy?
The absorption of infrared radiation
Molecular vibrations occur when bonds in a molecule move due to the energy absorbed from infrared radiation.
What do groups of atoms within a molecule absorb at characteristic frequencies?
Infrared radiation
Each group of atoms has a specific frequency at which it absorbs infrared radiation.
What can be deduced from infrared spectra using avenumber data?
Functional groups present in organic compounds
Avenumber data helps identify specific functional groups based on absorption patterns.
What is the percentage transmittance of a frequency that passes through a compound without absorption?
100%
In practice, this is never achieved due to some level of absorption.
What does a transmittance of 5% indicate?
Nearly all of that particular frequency is absorbed by the compound
This high absorption provides insights about the molecular bonds.
What happens to the bonds in a molecule when infrared light is absorbed?
They vibrate
This vibration is referred to as Molecular Vibrations.
What is the relationship between visible light and infrared radiation?
Both consist of a continuous range of electromagnetic frequencies
However, visible light can be detected by the human eye, while infrared radiation cannot.
True or False: Infrared radiation can be detected by the human eye.
False
Infrared radiation consists of frequencies that are invisible to the human eye.
How is the amount of a particular frequency that gets through a compound measured?
Percentage transmittance
This measurement indicates how much of the frequency is absorbed versus how much passes through.
What are the two ways vibrations occur?
Stretching vibration and bending vibration
What happens to the C-H bond when it absorbs infrared radiation?
The C-H bond stretches or bends
What factors determine the unique frequency at which each bond vibrates?
- Bond strength
- Bond length
- Mass of atom at either end of the bond
What is the range of wavenumbers in the IR spectrum?
300 - 4000 cm⁻¹
What occurs when bonds in a molecule vibrate in response to IR light?
They absorb energy from the IR light source
What is produced when the full IR spectrum is passed through a sample?
A trace called a spectrum
What do the peaks in the spectrum represent?
Absorbance troughs caused by a frequency of IR light being absorbed
True or False: Each peak in a spectrum is characteristic of a specific bond or atoms.
True
Fill in the blank: A sample cell is used for a solution of _______.
[sample]
What role does the reference cell serve in the IR analysis?
It is for solvent only
What does the chart recorder do in the IR analysis setup?
Records the IR spectrum
What is the characteristic feature of the neak?
Vibration of a particular group
The term ‘neak’ seems to be a typographical error for ‘peak’ in this context.
What is the fingerprint region in IR spectroscopy?
Region from about 1500 to 500 cm⁻¹ with complicated absorptions due to bending vibrations
It is difficult to identify individual bonds in this region.
Why is the fingerprint region important?
Each different compound produces a different pattern of troughs in this part of the spectrum
What does the peak on an IR spectrum correspond to?
Specific bonds and atoms vibrating or stretching
