infrared spectroscopy Flashcards
how does an infrared spectrometer work
a beam of radiation containing a spread of frequencies is passed through a sample
- the radiation that emerges is missing the frequencies that correspond to the types of bonds found in the sample
- the instrument plots a graph of the intensity of the radiation emerging from the sample, called the transmittance against the frequency of radiation.
- the frequency is expressed as a wavenumber
do stronger bonds vibrate faster or slower than weaker bonds
faster
but what I mean is at a higher freq
what is the fingerprint region
the area of an infrared spectrum below 1500cm^-1 - it has a unique shape which can used to identify substances,
what is the difference between spectroscopy and spectrometry
spectroscopy is a non-damaging technique to the sample
spectrometry is a damaging technique tot he sample
which kind of isotopes respond to nmr
odd numbers
what is a brief overview of nmr
a magnetic field is applied to the sample, which is surrounded by a source of radio waves and a radio receiver. this generates an energy change in the nuclei of atoms in the sample that can be detected. electromagnetic energy is emitted which can be interpreted by a computer
do carbon atoms in different functional groups feel the magnetic field the same way
no
why do different functional groups of carbon respond different to magnetic fields
it is dependent upon the amount of shielding
more shielding = less magnetic effect and lowers the frequency which resonates
what is chemical shift
related to the difference in frequency between the resonating nucleus and that of TMS
what happens when an electronegative element is in a compound
it draws the electron density towards itself therefore the other atom is less shielded and will have a higher frequency for which it resonates.
what is TMS
the zero reference signal
tetramethylsilane
which solvents do we use to dissolve TMS
CDCl3 or CCl4
what is D
deuterium
if hydrogen was used in nmr as a solevnt it would have its own peaks and disrupt the spectrum
what si the difference between CDCl3 and CCl4
CDCl3 is polar and CCl4 is not.
CCL4 is carcinogenic
what are the good things about TMS
- unreactive
- low bpt so it is easy to separate from sample molecule
- non-toxic
