Een infrarood (IR) spectrum laat zien welke functionele groepen aanwezig zijn in een organisch molecuul. Bij IR-spectroscopie wordt een molecuul bestraald met elektromagnetische straling. Het molecuul absorbeert energie als de frequentie van de straling overeenkomt met de frequentie van de trillingen van bindingen in het molecuul. Elk bindingstype absorbeert energie van een specifieke frequentie. Daarom kunt u de bindingstypen in een element bepalen door het IR-spectrum te meten. Het IR-spectrum is echter beperkt tot relatief kleine moleculen omdat er weinig kan worden vastgesteld aan de hand van IR-spectroscopie van grote moleculen met tientallen absorpties.
Bepaal de X-as en de Y-as van het spectrum. De X-as van een IR-spectrum is gelabeld als "Wapenummer" en varieert in aantal van 400 uiterst rechts tot 4.000 helemaal links. De X-as geeft het absorptienummer. De Y-as is gelabeld als "Percentage transmissie" en varieert in aantal van 0 aan de onderkant en 100 aan de bovenkant.
Bepaal de karakteristieke pieken in het IR-spectrum. Alle IR-spectra bevatten vele pieken. Bepaal echter de grote pieken in het spectrum omdat ze de gegevens leveren die nodig zijn om het spectrum te lezen.
Bepaal de gebieden van het spectrum waarin de karakteristieke pieken bestaan. Het IR-spectrum kan worden gescheiden in vier regio's. Het eerste gebied varieert van 4.000 tot 2.500. Het tweede gebied varieert van 2500 tot 2000. Het derde gebied varieert van 2000 tot 1500. Het vierde gebied varieert van 1500 tot 400.
Bepaal de functionele groepen die zijn geabsorbeerd in het eerste gebied. Als het spectrum een karakteristieke piek in het bereik van 4.000 tot 2.500 heeft, komt de piek overeen met absorptie veroorzaakt door N-H, C-H en O-H enkele bindingen.
Bepaal de functionele groepen die zijn geabsorbeerd in het tweede gebied. Als het spectrum een karakteristieke piek in het bereik van 2500 tot 2000 heeft, komt de piek overeen met absorptie veroorzaakt door drievoudige bindingen.
Bepaal de functionele groepen die zijn geabsorbeerd in het derde gebied. Als het spectrum een karakteristieke piek in het bereik van 2000 tot 1500 heeft, komt de piek overeen met absorptie veroorzaakt door dubbele bindingen zoals C = O, C = N en C = C.
Vergelijk de pieken in het vierde gebied met de pieken in het vierde gebied van een ander IR-spectrum. Het vierde staat bekend als het vingerafdrukgebied van het IR-spectrum en bevat een groot aantal absorptiepieken die een grote verscheidenheid aan enkele bindingen vormen. Als alle pieken in een IR-spectrum, inclusief die in het vierde gebied, identiek zijn aan de pieken van een ander spectrum, dan kunt u er zeker van zijn dat de twee verbindingen identiek zijn.
Waarschuwing
Sommige organische verbindingen zijn gevaarlijk. Wees voorzichtig bij het hanteren van deze verbindingen en voer ze door een IR-spectroscopie.
FAQ - 💬
❓ What is the wavelength of the IR spectrum?
👉 Infrared radiation (IR), also known as thermal radiation, is that band in the electromagnetic radiation spectrum with wavelengths above red visible light between 780 nm and 1 mm. IR is categorized as IR-A (780 nm-1.4 µm), IR-B (1.4-3 µm) and IR-C, also known as far-IR (3 µm-1 mm).
❓ What is the light source in IR spectroscopy?
👉 Which lamp is used in IR spectroscopy? For infrared spectroscopy, a Globar is employed as a thermal light source. It's a silicon carbide rod with a diameter of 5 to 10 mm and a length of 20 to 50 mm that's been electrically heated to 1,000 to 1,650°C (1,830 to 3,000 degrees Fahrenheit).
❓ How does IR spectroscopy work?
👉 An infrared spectrometer analyses a compound by passing infrared radiation, over a range of different frequencies, through a sample and measuring the absorptions made by each type of bond in the compound. This produces a spectrum, normally a 'plot' of % transmittance against wavenumber.
❓ What does low transmittance mean in IR?
👉 The transmittance shows the percentage of the IR that passes through the sample cell - so the lower it is, the more is absorbed.
❓ What is the wavelength and frequency of IR?
👉 Infrared (IR) has wavelengths λ between 780 nm and 1 mm, which corresponds to a frequency range from 300 GHz to 400 THz. In the second half of the 19th century, it became known that heat radiation and other electromagnetic waves, such as visible light or radio waves, were similar in nature.
❓ Why we prefer wave number instead of wavelength in IR?
👉 A Raman spectrum plotted on a wavelength scale would be very narrow and clustered. Wavenumber is very convenient since it also allows IR spectrum to be compared and is also a measure of energy.
FAQs
INFORMATION OBTAINED FROM IR SPECTRA
IR is most useful in providing information about the presence or absence of specific functional groups. IR can provide a molecular fingerprint that can be used when comparing samples. If two pure samples display the same IR spectrum it can be argued that they are the same compound.
What is the IR region of the spectrum? ›
The infrared portion of the electromagnetic spectrum is usually divided into three regions; the near-, mid- and far- infrared, named for their relation to the visible spectrum. The higher energy near-IR, approximately 14000-4000 cm-1 (0.8-2.5 μm wavelength) can excite overtone or harmonic vibrations.
What is the range of IR in spectroscopy? ›
Regions of the Infrared spectrum
Most of the bands that indicate what functional group is present are found in the region from 4000 cm-1 to 1300 cm-1. Their bands can be identified and used to determine the functional group of an unknown compound.
How to tell the difference between aldehydes and ketones in IR? ›
Aldehydes tend to come at slightly higher frequencies than ketones (H is less electron-donating than an alkyl group), but conjugation can also lower the frequency. In addition, there is a characteristic double peak at 2700 and 2800 cm-1.
What is the purpose of an infrared spectrum? ›
It is used by chemists to determine functional groups in molecules. IR Spectroscopy measures the vibrations of atoms, and based on this it is possible to determine the functional groups.
What causes infrared spectrum? ›
If an inorganic compound forms covalent bonds within an ion, it can produce a characteristic infrared spectrum. Main infrared bands of some common inorganic ions: Diatomic molecules produce one vibration along the chemical bond.
How do I get an IR spectrum? ›
Infrared spectra may be obtained from samples in all phases (liquid, solid and gaseous). Liquids are usually examined as a thin film sandwiched between two polished salt plates (note that glass absorbs infrared radiation, whereas NaCl is transparent).
In which region IR spectrum takes place? ›
Region of IR
| Region | Wavelength | Wavenumbers (V), cm-1 |
|---|
| Near | 0.78 -2.5 | 12800 - 4000 |
| Middle | 2.5 - 50 | 4000 - 200 |
| Far | 50 -100 | 200 -10 |
| Most Used | 2.5 -15 | 4000 -670 |
Jan 29, 2023
The infrared spectrum of a sample is recorded by passing a beam of infrared light through the sample. When the frequency of the IR is the same as the vibrational frequency of a bond or collection of bonds, absorption occurs.
What is the basic principle of IR spectroscopy? ›
IR spectroscopy detects the absorption of light by a compound, in the IR region of the electromagnetic spectrum. To absorb light a molecule must have a bond within its structure that can exhibit what is referred to as a 'dipole moment' which means electrons within a bond are not shared equally.
Infrared (IR, infrared light) has wavelengths λ between 780 nm and 1 mm, which corresponds to a frequency range from 300 GHz to 400 THz. In the second half of the 19th century, it became known that heat radiation and other electromagnetic waves, such as visible light or radio waves, were similar in nature.
What is infrared spectroscopy in simple terms? ›
In infrared spectroscopy, infrared radiation is passed through a sample of the organic compound and then into a detector which measures the intensity of the transmitted radiation at different wavelengths. Infrared absorbances are measured in wavenumbers, the reciprocal of wavelength, in units of cm⁻¹.
How to identify a ketone IR spectrum? ›
The carbonyl stretching vibration band C=O. of saturated aliphatic ketones appears at 1715 cm-1. Conjugation of the carbonyl group with carbon-carbon double bonds or phenyl groups, as in alpha, beta-unsaturated aldehydes and benzaldehyde, shifts this band to lower wavenumbers, 1685-1666 cm-1.
What is the interpretation of the IR spectrum? ›
The interpretation of infrared spectra involves the correlation of absorption bands in the spectrum of an unknown compound with the known absorption frequencies for types of bonds. This table will help users become more familiar with the process.
How to identify a ketone? ›
Dissolve the given organic compound in ethanol. To this solution, add an alcoholic solution of 2,4-dinitrophenyl hydrazine. Shake the mixture well. If there is a formation of yellow to orange precipitate then the given compound is an aldehyde or ketone.
What is the significance of the IR spectrum? ›
Thus, the IR spectrum identifies the various bonds and functional groups within the molecule. In addition, there are also vast libraries of IR spectra that help identify unknown compounds or, at least, place them into certain classes of molecules.
What does IR light detect? ›
An infrared camera detects the thermal energy or heat emitted by the scene being observed and converts it into an electronic signal. This signal is then processed to produce an image. The heat captured by an infrared camera can be measured with a high degree of precision.
What does IR spectrum tell you about organic molecules? ›
The IR spectrum of an organic compound is a unique physical property and can be used to identify unknowns by interpretation of characteristic absorbances and comparison with spectral libraries. IR spectroscopy is also used in quantitative techniques because of its sensitivity and selectivity.
What is the interpretation of the spectra of IR spectroscopy? ›
The interpretation of infrared spectra involves the correlation of absorption bands in the spectrum of an unknown compound with the known absorption frequencies for types of bonds. This table will help users become more familiar with the process.
