Chapter 17 - Spetroscopy

Question 1

When an organic compound is placed inside the mass spectrometer, what happens?

Answer 1

It loses an electron and forms a positive ion, which is called the molecular ion

Question 2

How to find the molecular ion?

Answer 2

It will be the largest peak furthest to the right

Question 3

What is the M+1 peak?

Answer 3

A very small peak after the molecular ion on the spectrometer

Question 4

Why is the M+1 peak formed?

Answer 4

Isotopes - normally due to the carbon-13 isotope

Question 5

What is fragmentation?

Answer 5

The process in which the molecular ion is broken down into smaller fragments

Question 6

What are the smaller peaks on a spectrometer caused by?

Answer 6

Fragments

Question 7

What two things are produced when a molecular ion is fragmented?

Answer 7

A positively charged ion and a free radical

Question 8

Out of the two things produced by fragmentation, which will be detected by the spectrometer?

Answer 8

The positively charged ion

Question 9

What does the unit m/z show?

Answer 9

It is a ration of mass to charge

Question 10

How is it possible to tell two compounds with the same Mr apart using mass spectrometry?

Answer 10

They have different structures so won’t produce the same fragments, which will be seen on the spectrum

Question 11

How to combine spectrometry techniques to work out a compound

Answer 11

1) Use the composition to work out the molecular mass of the compound
2) Work out what functional groups are in the compound from its infrared spectrum
3) Use the mass spectrum to work out the structure of the molecule

Question 12

What is the m/z value of CH3+ ion?

Answer 12

15

Question 13

What is the m/z value of a C2H5+ ion?

Answer 13

29

Question 14

What is the m/z value of a C3H7+ ion?

Answer 14

43

Question 15

What is the m/z value of a C4H9+ ion?

Answer 15

57

Question 16

How to calculate the number of carbon atoms in a compound using the spectrum?

Answer 16

(Height of M+1 peak/height of M peak) x 100

Question 17

What are the two ways in which a bond can move?

Answer 17

It can bend or it can stretch

Question 18

What happens when a bond absorbs infrared radiation?

Answer 18

They bend or stretch more

Question 19

What happens when a stretch occurs?

Answer 19

The distance between the two atomic centres increase and decrease

Question 20

What happens when a stretch occurs?

Answer 20

The bond angle changes

Question 21

What does the amount that a bond stretches or bends depend upon?

Answer 21

The mass of atoms in the bond

The strength of a bond

Question 22

Will stronger bonds vibrate more or less?

Answer 22

More

Question 23

When will a bond absorb infrared radiation?

Answer 23

When it has the same frequency as the bonds in the molecule

Question 24

What can infrared spectroscopy be used for?

Answer 24

Identifying different functional groups because they absorb different frequencies of infrared radiation

Question 25

The process of infrared spectroscopy

Answer 25

The sample is placed inside an infrared spectrometer A beam of IR radiation is passed through the sample The molecule absorbs some of the IR frequencies and the emerging beam is analysed to work out what frequencies these are A computer then plots transmission against wavenumber

Question 26

What is the fingerprint region?

Answer 26

Unique peaks that can be used to identify the molecule

Question 27

From an infrared spectrum, how do you identify the different functional groups?

Answer 27

Compare the frequencies against the ones found in the data table

Question 28

What will all organic compounds produce on a spectrum?

Answer 28

A peak between 2850 and 3100 from the C-H bond

Question 29

What are the three functional groups you should be able to identify from a spectrum?

Answer 29

O-H group in alcohols C=O group in aldehydes, ketones and carboxylic acids COOH group in carboxylic acids

Question 30

What will the spectrum of an alcohol show?

Answer 30

A peak between 3200 and 3600 because of the O-H group

Question 31

What will the spectrum of an aldehyde or ketone show?

Answer 31

A peak between 1630 and 1820 because of the C=O bond

Question 32

What will the spectrum of a carboxylic acid show?

Answer 32

A peak at between 1630 and 1820 caused by the C=O bond | A broad peak between 2500 - 3300 caused by the O-H group

Question 33

Main use of infrared spectroscopy

Answer 33

Breathalysers

Question 34

Why can infrared spectroscopy be used in breathalysers?

Answer 34

The intensity of the peaks of bonds associated with ethanol, e.g. C-H

Question 35

Why is infrared spectroscopy used to monitor the concentrations of polluting gases?

Answer 35

Peaks associated with the bonds found in the pollutants can be measured for intensity

Question 36

What is elemental analysis?

Answer 36

Use of percentage composition data to determine the empirical formula

Question 37

What is mass spectrometry?

Answer 37

Use of a molecular ion from a spectrum to determine the molecular mass

Question 38

What is infrared spectroscopy?

Answer 38

Use of absorption peaks from a spectrum to identify bonds and functional groups that are present