spectroscopy chp 17

Question 1

what is mass spectrometery used for

Answer 1

mass spectra can be used to identify the molecular mass of an organic compound and to gain further information about its structure

Question 2

what happens to an organic compound when placed in a mass spectrometer

Answer 2

it loses an electron and forms a positive ion, the molecular ion

Question 3

what does the mass spectrometer detect from the molecular ion

Answer 3

• detects the mass-to-charge ratio (m/z) of the molecular ion

Question 4

how do you find the molecular mass of a compound from the mass spectrum diagram

Answer 4

to find the molecular mass, the molecular ion peak has to be located

Question 5

what is the molecular ion peak

Answer 5

the molecular ion peak is the clear peak at the highest m/z value on the right-hand side of the mass spectrum

Question 6

what is the M + 1 peak and why does it exist

Answer 6

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

Question 7

what is fragmentation,in mass spectrometery

Answer 7

• some molecular ions break down into smaller pieces known as fragments, this is fragmentation

Question 8

what does fragmentation cause

Answer 8

the other peaks in a mass spectrum are caused by fragment ions, formed from the breakdown of the molecular ion

Question 9

what are the products of the simplest form of fragmentation

Answer 9

the simplest fragmentation breaks a molecular ion into 2 species- a positively charged fragment ion and a radical.

Question 10

can the mass spectrometer detect the products of fragmentation

Answer 10

Any positive ions formed will be detected by the mass spectrometer, but the uncharged radicals are not detected

Question 11

how can fragmentation be used to help to identify organic molecules

Answer 11

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

Question 12

what is the formula for working out the number of carbon atoms using M+ and M+1

Answer 12

Question 13

what are some modern uses for mass spectrometery

Answer 13

drug testing in sports

Question 14

what is a feature of covalent bonds that is crucial for infrared spectroscopy

Answer 14

covalent bonds poses energy and vibrate naturally about a central point, the atoms in molecules are therefore in constant motion

Question 15

How does temperature effect the vibrations of a covalent bond

Answer 15

the amount of vibration increasing with increasing temperature.

Question 16

what can covalent bonds do with infrared spectroscopy

Answer 16

the bonds can absorb infrared (IR) radiation, which makes them bend or stretch more

Question 17

what are the 2 types of vibrations of covalent bonds

Answer 17

• stretching
• bending

Question 18

what is stretching vibrating

Answer 18

stretching is a rhythmic movement along the line between the atoms so that the distance between the 2 atomic centres increases and decreases

Question 19

what is bend vibrating

Answer 19

results in a change in bond angle

Question 20

what effects the amount a bond bends/stretchs

Answer 20

• 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)

Question 21

what radiation can bonds absord

Answer 21

radiation that has the same frequency as the natural frequency of the bond

Question 22

what do chemists use instead of frequency in spectroscopy

Answer 22

wavenumber

Question 23

How is does radition absorbtion in bonds lead to global warming

Answer 23

• 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

Question 24

explain the steps to how infrared spectroscopy works

Answer 24

• 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

Question 25

where can you find the fingerprint region

Answer 25

below 1500 cm^-1

Question 26

what is the fingerprint region

Answer 26

• unique peaks which can be used to identify a particular molecule under investigation

Question 27

what is one peak that all organic compounds have
what is its wavenumber

Answer 27

• C-H
• 2850 - 3100 cm^-1

Question 28

what are some modern day applications of infrared spectroscopy

Answer 28

• breathalysers

Question 29

what is the typical sequence of identification of an organic molecule

Answer 29

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