spectroscopy chp 17 Flashcards
what is mass spectrometery used for
mass spectra can be used to identify the molecular mass of an organic compound and to gain further information about its structure
what happens to an organic compound when placed in a mass spectrometer
it loses an electron and forms a positive ion, the molecular ion
what does the mass spectrometer detect from the molecular ion
- detects the mass-to-charge ratio (m/z) of the molecular ion
how do you find the molecular mass of a compound from the mass spectrum diagram
to find the molecular mass, the molecular ion peak has to be located
what is the molecular ion peak
the molecular ion peak is the clear peak at the highest m/z value on the right-hand side of the mass spectrum
what is the M + 1 peak and why does it exist
a very small peak one unit after the M+ peak
the m + 1 peak exists because 1.1 % of carbon is present as the carbon-13 isotope
what is fragmentation,in mass spectrometery
- some molecular ions break down into smaller pieces known as fragments, this is fragmentation
what does fragmentation cause
the other peaks in a mass spectrum are caused by fragment ions, formed from the breakdown of the molecular ion
what are the products of the simplest form of fragmentation
the simplest fragmentation breaks a molecular ion into 2 species- a positively charged fragment ion and a radical.
can the mass spectrometer detect the products of fragmentation
Any positive ions formed will be detected by the mass spectrometer, but the uncharged radicals are not detected
how can fragmentation be used to help to identify organic molecules
the mass spectra of each compound is unique, as molecules will all fragment in slightly different ways depending on their structures.
Mass spectra can therefore be used to help identify molecules
what is the formula for working out the number of carbon atoms using M+ and M+1
what are some modern uses for mass spectrometery
drug testing in sports
what is a feature of covalent bonds that is crucial for infrared spectroscopy
covalent bonds poses energy and vibrate naturally about a central point, the atoms in molecules are therefore in constant motion
How does temperature effect the vibrations of a covalent bond
the amount of vibration increasing with increasing temperature.
what can covalent bonds do with infrared spectroscopy
the bonds can absorb infrared (IR) radiation, which makes them bend or stretch more
what are the 2 types of vibrations of covalent bonds
- stretching
- bending
what is stretching vibrating
stretching is a rhythmic movement along the line between the atoms so that the distance between the 2 atomic centres increases and decreases
what is bend vibrating
results in a change in bond angle
what effects the amount a bond bends/stretchs
- the mass of the atoms in the bond
^heavier atoms vibrate more slowly than lighter atoms (heavier harder to bend) - the strength of the bond
^stronger bonds vibrate faster than weaker bonds (stronger bonds less easy to bend/stretch)
what radiation can bonds absord
radiation that has the same frequency as the natural frequency of the bond
what do chemists use instead of frequency in spectroscopy
wavenumber
How is does radition absorbtion in bonds lead to global warming
- carbon dioxide and methane absorb IR radiation from the sun
- bonds in these molecules re-emit energy, increasing temperature of atmosphere
^leads to global warming
explain the steps to how infrared spectroscopy works
- 1) sample under investigation placed inside IR spectrometer
- 2)beam of IR radiation with range 200-4000 cm^-1 is passed through the sample
- 3)molecule absorbs some IR frequencies
- emerging beam of radiation analysed to identify frequencies absorbed by sample
where can you find the fingerprint region
below 1500 cm^-1
what is the fingerprint region
- unique peaks which can be used to identify a particular molecule under investigation
what is one peak that all organic compounds have
what is its wavenumber
- C-H
- 2850 - 3100 cm^-1
what are some modern day applications of infrared spectroscopy
- breathalysers
what is the typical sequence of identification of an organic molecule
elemental analysis
- use of percentage composition data to determine empirical formula
mass spectrometry
- use of molecular ion peak from a mass spectrum to determine molecular mass
- use of fragment ions to identify sections of a molecule
infrared spectroscopy
- use of absorption peaks from an infrared spectrum to identify bonds and functional groups present in the molecule
