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The mass spectrometer can give information about the relative isotopic abundances of different elements

Antimony has two isotopes 121-Sb and 123-Sb. In a bullet at a crime scene there was a sample of antimony containing 57.3% 121-Sb and 42.7% 123-Sb. Calculate the relative atomic mass of the sample of antimony from the bullet.

This type of data may also be presented in graphical form from a mass spectrometer.

Tungsten M/Z Relative abundance

Chlorine Relative atomic mass Relative abundance

Complete Question 1 and 2 on page 171

Complete the isotopes exam questions Finish for prep

What do you remember about mass spectrometry?

Make a spider chart on the uses of mass spectrometry

Identifying organic compounds Organic molecules do not hold charge well. The ions break up or fragment. They break into smaller ions and neutral fragments. They do this in regular patterns. i.e. the same molecule always fragments in the same way. This allows us to analyse them.

Mass spectrum of propan-1-ol

Mass Spectrum of ethanol Molecular ion: tells you the molecular mass of the whole compound.

Mass Spectrum of ethanol: Identify the fragments responsible for the following peaks:

+ Possible fragments M

Identify the fragments responsible for the peaks at 15, 29 and 44 and thus identify this alkane.

Mass Spectrum of an alcohol. Identify the alcohol and draw structures for the fragment ions represented by the peaks at: 60, 59, 43, 31 and 29.

Possible fragments M

IR spectroscopy All molecules absorb Infra-red radiation The absorbed energy makes covalent bonds vibrate (bending or stretching)

All molecules absorb infrared radiation; absorbing energy makes the bonds vibrate. Every bond vibrates at its own frequency, dependant upon bond strength, bond length and the mass of atoms involved in bond. STRETCHING BENDING

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How IR spectroscopy works… Shine a range of IR frequencies, one at a time through a sample of organic compound and at some of the frequencies the energy will be absorbed. A detector on the other side of the sample would show that some frequencies are absorbed whilst others are not.

If a particular frequency is being absorbed as it passes through the compound being investigated, it must mean that its energy is being transferred to the compound. Energies in infra-red radiation correspond to the energies involved in bond vibrations.

Bend and Stretch In covalent bonds, atoms aren't joined by rigid links; the two atoms are held together because both nuclei are attracted to the same pair of electrons. The two nuclei can vibrate backwards and forwards - towards and away from each other - around an average position.

Fingerprint regions You must be able to identify the following peaks. – C-H in alkanes/alkenes/aldehydes – O-H in alcohols/carboxylic acids – N-H in amines – C=O in aldehydes and ketones – C-X in halogenoalkanes You will have data books in exam, if required.

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C-O in alcohols, esters & carboxylic acids C=O in aldehydes and ketones C-H in alkanes/alkenes/aldehydes O-H in carboxylic acids (very broad) O-H in alcohols/carboxylic acids (broad) Identify the group next to the yellow box using the key below.

C-O in alcohols, esters & carboxylic acids C=O in aldehydes and ketones C-H in alkanes/alkenes/aldehydes O-H in carboxylic acids (very broad) O-H in alcohols/carboxylic acids (broad) Identify the groups next to the yellow boxes using the key below.

C-O in alcohols, esters & carboxylic acids C=O in aldehydes, ketones & carboxylic acids C-H in alkanes/alkenes/aldehydes O-H in carboxylic acids (very broad) N-H in amines/amides O-H in alcohols/carboxylic acids (broad)

Whiteboard quiz

Quiz 1) Identify the species responsible for the peak at m/z = 29

2) Structural formula of 1- chlorobutane

3) What is the mass of the molecular ion?

4) Skeletal formula of ethanol

5) How do you get from an alcohol to a carboxylic acid?

6) What is missing?

C-O in alcohols, esters & carboxylic acids C=O in aldehydes and ketones C-H in alkanes/alkenes/aldehydes O-H in carboxylic acids (very broad) O-H in alcohols/carboxylic acids (broad) 7) Identify the group next to the yellow box.

8) Draw the mechanism for the reaction of ethene with Hydrogen Bromide