IR Absorption Spectroscopy Flashcards
___ refers to the part of the infrared spectrum that is closest to VISIBLE LIGHT and ___ refers to the part that is
closer to the MICROWAVE region
mid IR region ____ mm however, when it comes to wavenumber it extends to the range of ____
Near-infrared
far-infrared
Mid IR region (2.5 mm-15 mm)
650 cm^-1 to 4000 cm ^-1
IR Active species
Molecular species with ___ between various VIBRATIONAL and ROTATIONAL states (___)
ONLY BONDS with significant ___ will absorb INFRARED RADIATION
small energy differences (Most Organic species)
Dipole Moments
Bonds which DO NOT absorb infrared include: (2)
Symmetrically substituted alkenes and alkynes
R-C=C-R
R>=<R
Symmetric diatomic molecules
H2 , Cl2, O2, N2
____ like ___ and ___ absorb only in the FAR IR REGION ( <700 cm^-1) so are suitable only as SAMPLE HOLDERS for most MID-IR measurements
Ionic Salts
NaCl
Kbr
IR RADIATION IS PASSED THROUGH A SAMPLE.
Some of the infrared
radiation is____ , the rest is ____. The resulting spectrum represents the MOLECULAR ABSORPTION and
TRANSMISSION, creating a MOLECULAR FINGERPRINT of the sample.
NONE of two unique molecular structures PRODUCE THE SAME infrared spectrum —This makes infrared spectroscopy useful
for several types of analysis.
Absorbed
Transmitted
SAMPLE HANDLING:
True or False: Good solvents that are transparent throughout the region of interest allow for ease in sample handling
NO GOOD SOLVENTS EXIST THAT ARE TRANSPARENT THROUGHOUT the region of interest.
As a consequence, sample handling is frequently the most difficult and time-consuming part of an infrared spectrometric analysis.
SAMPLE HANDLING:
The spectrum of a low-boiling liquid or gas
can be obtained by permitting the sample to:
EXPAND into an ___ equipped with SUITABLE WINDOWS
evacuated cylindrical cell
SAMPLE HANDLING:
Cells:
___ are most commonly
employed; even with care, however, their surfaces eventually become fogged due to absorption of moisture.
Polishing with a ___ returns them to their original condition.
Sodium chloride windows
buffing powder
SAMPLE HANDLING:
Liquids:
When the amount of liquid SAMPLE IS SMALL or when a suitable SOLVENT UNAVAILABLE, it is common practice to obtain spectra on ___.
A drop of the (answer above) is squeezed between two ___ to give a layer that has a thickness of ___. The two plates, held together are then mounted in the beam path.
Such a technique DOES NOT
GIVE REPRODUCIBLE ____
HOWEVER, SPECTRA are usually SATISFACTORY for QUALITATIVE INVESTIGATIONS
Pure (neat) liquid
rocksalt plates
0.01 mm or less
Transmittance data
SAMPLE HANDLING:
Solids:
Most ORGANIC COMPOUNDS exhibit NUMEROUS ABSORPTION PEAKS throughout the ____,
BECAUSE OF THAT FINDING A SOLVENT WITHOUT ____ IS IMPOSSIBLE.
As a consequence, spectra are often obtained on DISPERSIONS OF THE SOLID in a ____ or ____
mid-infrared region
OVERLAPPING PEAKS
liquid or solid matrix
SAMPLE HANDLING:
Pelleting:
One of the most popular techniques for handling solid samples has been ___.
Milligram or less of the finely ground sample is intimately mixed with about ____.
The mixture is then pressed in a die at ___to yield a ___ DISK.
The DISK is then held in the INSTRUMENT BEAM FOR SPECTROSCOPIC EXAMINTION for spectroscopic examination.
KBr pelleting.
100 mg of dried potassium bromide powder.
TRANSPARENT disk
10,000 to 15,000 pounds per square inch
SAMPLE HANDLING:
Mulls:
Infrared spectra of solids that are NOT SOLUBLE IN AN INFRARED-TRANSPARENT SOLVENT or are NOT CONVENIENTLY PELLETED in KBr are often obtained by:
DISPERSING THE ANALYTE in a ___ or ___.
Mulls are formed by grinding ___ of the FINELY POWDERED SAMPLE in the presence of ____.
The resulting mull is then examined as a FILM between flat ___.
mineral oil
fluorinated hydrocarbon mull
2 to 5 mg finely powdered sample
one or two drops of a heavy hydrocarbon oil (Nujol).
salt plates
Aside from Mid IR being the most widely used
The NEAR-INFRARED region from 4000 to 14,000 cm-1 (0.75 to 2.5 mm) also finds considerable use for the ____
The FAR-INFRARED region has been for the determination of the structures of ____
routine QUANTITATIVE determination (agricultural, food, petroleum, chemical – determination of water, determination of phenols – celluluse, oil)
inorganic and metal-organic species.
Virtually all infrared instrument manufactures now offer
____ to assist chemist in identifying
compounds from stored infrared spectral data
a peak profile,can be compared with profiles of pure compounds stored.
computer search systems
Difference between Infrared Absorption and Ultraviolet/Visible Spectroscopic methods (3)
greater COMPLEXITY of the spectra,
the NARROWNESS of the absorption bands,
the instrumental LIMITATIONS of INFRARED INSTRUMENTS (inferior)
