Chapter 17 - Spectroscopy

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

Bend or stretch

Question 18

What happens when a bond absorbs infrared radiation?

Answer 18

Making it bend or stretch

Question 19

What happens when a stretch occurs?

Answer 19

Rhythmic movement along the line between the atoms so that the distance between the two atomic centres increase and decrease

Question 20

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

Answer 20

• The mass of the atom in the bond (heavier atoms vibrate more slowly than light atoms)
• The strength of the bond (Stronger bonds vibrate faster than weaker bonds)

Question 21

Will stronger bonds vibrate more or less?

Answer 21

More

Question 22

When will a bond absorb infrared radiation?

Answer 22

Radiation can be absorbed when it has the same frequency as natural frequency of the bond

Question 23

What can infrared spectroscopy be used for?

Answer 23

Identifies the functional groups present in organic molecules

Question 24

The process of infrared spectroscopy

Answer 24

1) The sample under investigation is placed inside in IR spectrometer
2) A beam of IR Radiation in the range 200–4,000 cm^-1is passed through the sample
3) molecules absorb some of the IR frequencies, the emerging beam radiation is analysed to identify the frequency that Have been absorbed by the sample
4) the IR spectrometer is usually connected to a computer that plots a graph of transmittance against the wavenumber

Question 25

What is the fingerprint region?

Answer 25

Unique peaks unique peaks which can be used to identify the particular molecule under investigation

Question 26

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

Answer 26

Tables of data used to help identify particular functional group on an unknown molecule (identification by wave number)

Question 27

What will all organic compounds produce on a spectrum?

Answer 27

C-c and c-H

Question 28

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

Answer 28

• O-H in alcohols
• C- - O in aldehydes, Ketones, carboxylic acids
• COOH in carboxylic acid

Question 29

What will the spectrum of an alcohol show?

Answer 29

Absorbance peak in 3200-3600 range by O-H bond

Question 30

What will the spectrum of an aldehyde or ketone show?

Answer 30

Absorbance peake in 1630 to 1820 range by C- - O

Question 31

What will the spectrum of a carboxylic acid show?

Answer 31

Absorbance peak in 1630 to 1820 (C- - O) and broad peak 2500-3330 (O-H)

Question 32

Main use of infrared spectroscopy

Answer 32

• pollutants can be intensified

* Breathalyser

Question 33

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

Answer 33

Can detect and measure carbon monoxide, carbon dioxide and hydrocarbons in a busy town centre is to monitor localised pollution

Question 34

What is elemental analysis?

Answer 34

Use of percentage composition data to determine the empirical formula

Question 35

What is mass spectrometry?

Answer 35

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

Question 36

What is infrared spectroscopy?

Answer 36

Use of absorption peaks from an infrared spectrum to identify bonds and functional groups present in the molecule