Module 4 Chapter 17 Flashcards

1
Q

What is a mass spectrometer used from

A

To identify the molecular mass (Mr) of an unkown (or known) compound

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2
Q

What is the molecular ion (M+)

A

The organic compound that is put into the mass spectrometer, loses an electron and forms a positive ion.

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3
Q

What does a mass spectrometer detect and what does this tell is

A

it detects the mass:charge ratio —> this gives the molecular mass of the compounds.

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4
Q

Where is the molecular ion peak located

A

It is the furthest peak found to the right of your mass spectrum (has the highest m/z value)

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5
Q

What is the small peak after M+ and why does it exist

A

The M+1 peak
And it exists due to 1.1% of carbon being the carbon-13 isotope

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6
Q

What is a fragment

A

It is caused when a molecular ion breaks down into smaller pieces called fragments

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7
Q

What are the other parts of a mass spectrum caused by

A

By fragment ions which are formed from the breakdown of the molecular ion.

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8
Q

What does the simplest fragmentation do

A

It breaks down the molecular ion into two species:
The positively charged fragment ion and a radicals

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9
Q

What is detected by the mass spectrometer

A

The positively charged ion fragments are detected however uncharged radicals are not

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10
Q

What is a feature of a mass spectrum and why

A

It is unique for each compound
As they all fragment in different ways depending on their structure

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11
Q

What can you use fragments to do

A

As clues to build and identify molecules

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12
Q

What are the stages of a mass spectrometer working

A

Ionisation, acceleration, deflection and detecting

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13
Q

What is the most abundant peak called

A

The base peak

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14
Q

What are features of a mass spectrum

A

the molecule is ionised and fragmented

The fragment with the greatest mass/charge ratio is called the molecular ion

The parent ion gives the molecular mass

The base peak is the most intense peak

Isotope peaks may be observed with intensities determined by the abundance of isotopes

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15
Q

What is a disadvantage of a mass spectrum

A

You are destroying the sample when analysing it

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16
Q

What does IR (infrared radiation) do

A

It causes covalent bonds to vibrate more and absorb energy

17
Q

What is a feature of the IR energy that molecules absorb

A

They absorb IR energy at a frequency corresponding to the frequency of the bonds natural vibration

18
Q

What happens when the bonds absorb IR

A

They bend and stretch more

19
Q

What does the IR detect

A

How the absorption of a sample varies with wave number cm ^-1, which is proportional to the frequency of the vibration of bonds in the molecule.

20
Q

What is IR used to do

A

Identify the functional groups that are present in a molecule

21
Q

What can IR be absorbed by (atmosphere) and what can it cause

A

It can be absorbed by atmospheric gases containing C=O, O-H and C-H bonds which is the suspect link to global warming and resulting changes to energy usage.

22
Q

What do the bonds that absorb the energy in these gases do

A

The vibrating bonds re-emit the absorbed energy from the sun as radiation that increases the temperature of the atmosphere close to the earths surface leading to global warming.

23
Q

What are the three factors affecting vibration and why

A

Type of vibration: absorptions due to bending tend to occur at lower wave numbers than stretching

Strength of bonds: stronger bonds absorb higher wave numbers

Mass of atoms: heavier atoms vibrate at lower frequencies than lighter ones

24
Q

How can IR be used to identify functional groups

A
  1. Sample placed in Ir spec
  2. A beam of Ir radiation (200-4000 cm^-1) is passed through the sample
  3. Molecule absorbs some IR frequencies, the emerging beam is analysed
  4. connected computer plots graph of transmittance against wave number
25
Q

What are the dips in the graph called and what do they show

A

They are called peaks and each peak is observed at a wave number that is related to a particular bond in a molecule.

26
Q

What is the fingerprint region

A

Below 1500 cm^-1
Unique peaks which can be used to identify a particular molecule
Difficult to predict with certainty what functional groups the peaks relate to
Easier outside this region

27
Q

What are some common bonds and their characteristics of the peaks

A

O-H group in alcohols (broad peaks)
C=O groups in aldehydes, ketones and CA (narrow)
All organic molecules produce a characteristic peak between 2850-3100 Cm^-1 due to C-H bonds

28
Q

What are uses of IR

A

They measure carbon monoxide, CO2 and hydrocarbon levels in bust town centres or by motorways to monitor car pollution

Ir spectrometers that look specifically for absorptions around 1050 Cm^-1 ( corresponding to the vibration of C-O bonds in ethanol)