spectroscopy Flashcards
what is spectroscopy ?
the use of radiation to observe changes in moclules
what is within the methods of spectroscopy ?
- use a tiny amount of sample
- are non destructive
how will the infrared radiation be absorbed by ?
by the bonds in molecules causing vibrations
what are the two common vibrations ?
stetches and bends
a molecule will only absorb a significant amount of infrared radiation if what ?
there is a change in the dipole moment (polarity) following a vibration
what do greenhouse gases do ?
absorb infrared and reemit it toward the Earth ( trapping heat )
what is the power as a greenhouse gas - nitrogen / oxygen ? Reason ?
no effect at all - no polarity so symmetrical and no polar bond
what is the power as a greenhouse gas - water vapour ? Reason ?
very strong but short lived - polar so asymmetrical and polar bond but will condense and rain
what is the power as a greenhouse gas - methane ? Reason ?
moderate - not polar so weakly polar bonds, symmetrical and has more bonds and can stretch and bend asymmetrically
what is the power as a greenhouse gas - nitrogen oxides ? Reason ?
strong - polar bonds and asymmetrical
what is the power as a greenhouse gases - carbon dioxide? Reason ?
weak - non polar can stretch asymmetrically so bending is unlikely due to pi bonding
what is the power as a greenhouse gas - CFCs and SF6? Reason ?
very strong - strong polar bonds and asymmetrical
what two pieces of information does an IR spectrometer hep determine the identity of a molecule ?
transmittance of IR
wavenumber - energy
what is the transmittance ?
the amount of infrared radiation that passes through the analyte
the lower the transmittance the more of what is present
bond
what does the wavenumber describe ?
the energy of the infrared radiation
the higher the wavenumber, …
the higher the energy
what is a change in dipole moment ?
following the vibration the delta positive / negative of the molecule will change
when will there be a change in dipole moment ?
the molecule needs to polar so has to have a polar bond and lack symmetry
what are the five stages of mass spectrometry called ?
stage 1: vaporisation
stage 2: ionisation
stage 3 : acceleration
stage 4 : deflection
stage 5: detection
Stage 1: vaporisation
in order to pass through the spectrometer the sample must be vaporised using heat or electrical energy
Stage 2 : ionisation
a beam of high energy electrons are fired at the analyte molecules - knock electrons from the molecule
ionisation:
M -> M+ (e-)
what is this called ?
molecular or parent ion
what is fragmentation ?
the energy from the electron can also cause fragmentation of the molecular ion
Stage 3 : acceleration
an electric field is then used to accelerate any ions formed ionisation and fragmentation
stage 4 : deflection
a magnetic field is used to deflect ions toward detector
what does the mass and charge of the ion determine ?
if it reaches the detector
Stage 5 : detection
the ions hit a metal copper plate which emits electrons - creates a current which detects the ion
the relative intensity number of that mass/ charge ion is then recorded
what is mass/ charge called ?
m/z of a ion
how is mass spectrometry identify its molecules by their mass to charge ratio achieved by ?
-ionising the unknown molecule
-accelerating the ions using an electric field
-deflecting the ions using a magnetic field
-detecting the ions to calculate their mass/ charge
ionisation
m + e- -> [M]+. + 2e-
unknown molecule + high energy electron -> parent ion
C3H8 + e- -> [C3H8]+. + 2e-
what does the size of a peak show ?
how stable the ion is
the more stable ions typically be secondary / tertiary carbocations
these make larger peaks on mass spectra
when fragmenting your molecule how many bonds would you break ?
only one bond - starts with single bond
