Chapter 17 - Spectroscopy

Question 1

IR spectroscopy- the degree of vibration depends on?

Answer 1

• Bond strength - stronger bonds vibrate ar a higher freq
• Bond length
• Mass of atoms - heavier atoms vibrate at a lower freq

Question 2

Mass Spectrometry - watch out for?

Answer 2

• the M+1 peak
• this can appear due to the presence of C-13
• usually appears in more sig % in larger mols

Question 3

2 isomers have the same:?

Answer 3

• molecular formula

- molecular ion peak (same Mr)

Question 4

2 isomers have diff?

Answer 4

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

Question 5

covalent bonds do what when they absorb IR radiation?

Answer 5

vibrate

Question 6

what types of vibration can occur?

Answer 6

a stretch or a bend

Question 7

what can be displayed on an infra red spectrum as a wavenumber?

Answer 7

these absorbed energies

Question 8

fingerprint region?

Answer 8

is below 1500cm^-1 - too many bonds to identify so just ignore

Question 9

all organic compounds will show?

Answer 9

C-H peak

Question 10

IR spectra only really tells us?

Answer 10

which FGs are in a molecule

Question 11

Where is the best place to start w an IR spectra?

Answer 11

• 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

Question 12

⭐ IR spectra - must include?

Answer 12

absorbance units

Question 13

⭐ IR spectra - look at?

Answer 13

trough - bottom eventhough it’s called a peak!!!!

Question 14

which molecules absorb Infra-red radiation in the atmosphere?

Answer 14

atmospheric gases containing C=O, O-H, C-H bonds (e.g. H2O, CO2, CH4) - greenhouse gases

Question 15

what 2 things can happen to infrared radiation from the sun that passes through the Earth’s atmosphere?

Answer 15

• absorbed by Earth’s surface

- OR re-emitted from the Earth’s surface in the form of longer wavelength IR radiation

Question 16

how are molecules of CH4, CO2, H2O affected by IR radiation?

Answer 16

• 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

Question 17

e.g.s of incentives available to encourage ppl to reduce CO2 emissions?

Answer 17

• 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

Question 18

uses of IR spectroscopy- gas monitoring?

Answer 18

• 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

Question 19

uses of IR spectroscopy- breathalysers?

Answer 19

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

Question 20

mass spectrometry uses in general?

Answer 20

• to identify compounds
• to determine the abundance of each isotope of an element
• to get further info abt the structure of mols

Question 21

mass spectometry uses specific?

Answer 21

• 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

Question 22

⭐ mass spec…

Answer 22

can be used to determine relative isotopic mass and rom this we can calc RAM

Question 23

the relative atomic mass found by the space probe was diff to the relative atomic mass on Earth- suggest why?

Answer 23

different isotopes or diff abundances of the same isotopes as those found on earth

Question 24

what happens in a mass spectometer?

Answer 24

sample mols are turned into ions and their mass: charge ratio is measured

Question 25

mass spec can be used to?

Answer 25

• 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

Question 26

M^+ peak is at?

Answer 26

the highest m/z ratio

Question 27

What determines how much these gases impact on

warming up the atmosphere?

Answer 27

The concentration of the gases and their ability to

absorb ir radiation, the no. of bonds that absorb IR radiation

Question 28

what is the most stable peak?

Answer 28

The tallest peak = fragment ion is most stable= base peak

Question 29

O-H peak is usually what shape?

Answer 29

rounded

Question 30

what do u need to include in a mass spec answer?

Answer 30

quoted data and the bond

Question 31

what is the M + 1 peak?

Answer 31

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

Question 32

what can the M+1 peak b used for?

Answer 32

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

Question 33

what is a stretch?

Answer 33

a rythmic movement along the line between the atoms so that the distance between the 2 atomic centres increases and decreases.

Question 34

What does a bend result in?

Answer 34

a change in bond angle

Question 35

the amount that a bond stretches or bends depends on?

Answer 35

• 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