Chapter 17 - Spectroscopy Flashcards
IR spectroscopy- the degree of vibration depends on?
- Bond strength - stronger bonds vibrate ar a higher freq
- Bond length
- Mass of atoms - heavier atoms vibrate at a lower freq
Mass Spectrometry - watch out for?
- the M+1 peak
- this can appear due to the presence of C-13
- usually appears in more sig % in larger mols
2 isomers have the same:?
- molecular formula
- molecular ion peak (same Mr)
2 isomers have diff?
fragment patterns bc diff fragment ions will be formed, diff fragment peaks will be produced - this can be used to identify and differentiate the indiv isomers
covalent bonds do what when they absorb IR radiation?
vibrate
what types of vibration can occur?
a stretch or a bend
what can be displayed on an infra red spectrum as a wavenumber?
these absorbed energies
fingerprint region?
is below 1500cm^-1 - too many bonds to identify so just ignore
all organic compounds will show?
C-H peak
IR spectra only really tells us?
which FGs are in a molecule
Where is the best place to start w an IR spectra?
- start by looking for a C=O, if that is present u must have an aldehyde, ketone or CA
- 2nd bond to look for is the OH bond, - is in alcohols and CA s
⭐ IR spectra - must include?
absorbance units
⭐ IR spectra - look at?
trough - bottom eventhough it’s called a peak!!!!
which molecules absorb Infra-red radiation in the atmosphere?
atmospheric gases containing C=O, O-H, C-H bonds (e.g. H2O, CO2, CH4) - greenhouse gases
what 2 things can happen to infrared radiation from the sun that passes through the Earth’s atmosphere?
- absorbed by Earth’s surface
- OR re-emitted from the Earth’s surface in the form of longer wavelength IR radiation
how are molecules of CH4, CO2, H2O affected by IR radiation?
- absorb longer wavelength IR radiation as it has the same freq as the natural freq of their bonds.
- eventually, the vibrating bonds in these molecules re-emit this energy as radiation that ⬆ the temp of the atmosphere close to the Earth’s surface, leading to global warming
e.g.s of incentives available to encourage ppl to reduce CO2 emissions?
- money/ grants to put solar panels on roof or to insulate loft, cavity wall, ect.
- Buy-back schemes for excess electricity generated by solar panels
- cycle/walk to work schemes to reduce car use
uses of IR spectroscopy- gas monitoring?
- to monitor gases causing air pollution (e.g. CO and NO from car emissions) - fingerprint region is very good for this, <1500cm-1 gives a unique pattern for every mol that can be identified by a computer with a database for spectra
uses of IR spectroscopy- breathalysers?
in modern breathalysers to measure ethanol in the breath, IR breathalysers detect the OH bonds in alc mols. The more radiation absorbed the more alc in the blood
mass spectrometry uses in general?
- to identify compounds
- to determine the abundance of each isotope of an element
- to get further info abt the structure of mols
mass spectometry uses specific?
- monitoring the breath of patients during surgery
- detecting banned substances like steroids in sport
- analysing mols in space
- detecting traces of toxic chemicals in marine environments
⭐ mass spec…
can be used to determine relative isotopic mass and rom this we can calc RAM
the relative atomic mass found by the space probe was diff to the relative atomic mass on Earth- suggest why?
different isotopes or diff abundances of the same isotopes as those found on earth
what happens in a mass spectometer?
sample mols are turned into ions and their mass: charge ratio is measured
mass spec can be used to?
- analyse molecules and we can find out the molecular mass of the molecule from its molecular ion peak, a.k.a M^+ peak
- when the mol splits into pieces, a unique fragmentation pattern is seen on the spectra
M^+ peak is at?
the highest m/z ratio
What determines how much these gases impact on
warming up the atmosphere?
The concentration of the gases and their ability to
absorb ir radiation, the no. of bonds that absorb IR radiation
what is the most stable peak?
The tallest peak = fragment ion is most stable= base peak
O-H peak is usually what shape?
rounded
what do u need to include in a mass spec answer?
quoted data and the bond
what is the M + 1 peak?
there is usually a very small peak one unit aftr the M+ peak. It exists bc 1.1% of C is present as the C-13 isotope
what can the M+1 peak b used for?
to identify the no. of C atoms present in the molecules of an organic compound.
No. of C atoms = Height of M+1 peak/ height of M peak x100
what is a stretch?
a rythmic movement along the line between the atoms so that the distance between the 2 atomic centres increases and decreases.
What does a bend result in?
a change in bond angle
the amount that a bond stretches or bends depends on?
- the mass of the atoms in the bond - heavier atoms vibrate more slowly than lighter atoms
- the strength of the bond - stronger bonds vibrate faster than weaker bonds
