Modern Analytical Techniques I

Question 1

What can be obtained from a mass spectrum?

Answer 1

Information about the molecular structure of an organic molecule

Question 2

What is the first thing to look for in a mass spectrum?

Answer 2

The peak due to molecular ion - normally has highest m/z value

Question 3

What is the molecular ion peak a result of?

Answer 3

Result of the organic molecules losing an electron in the mass spectrometer

Question 4

What is the M+1 peak caused by?

Answer 4

Caused by the presence of carbon-13 isotope

Question 5

What are the peaks with smaller m/z value a result of?

Answer 5

Fragmentation in the mass spectrometer, rearrangement reactions and the loss of more than one electron.

Question 6

What does the ionisation process do to the molecular ion?

Answer 6

Causes the molecular ion to be in a high-energy state

Question 7

What are the two fragments that many ions break into?

Answer 7

A neutral species (radical) and a positive ion

Question 8

How can a functional group be identified?

Answer 8

A functional group causes molecules to breeze a apart in a characteristic way.

Question 9

Common fragment lost? 15, 17, 28, 29, 31 ,45, 77

Answer 9

15- CH3+    
17- OH+  
28-CO+.                      
29- C2H5, CHO+     
31-CH20H+   
45-COOH.    
77-C6H5

Question 10

What fragments can be derived from ethane?

Answer 10

Forms a methyl cation and methyl radical

Question 11

What fragments can be derived from propane?

Answer 11

A methyl cation and ethyl cation in its spectrum

Question 12

Are radicals detected in mass spectrometer? So..

Answer 12

They are not detected so all the peaks formed by fragmentation are caused by positive ions.

Question 13

What does the base peak demonstrate?

Answer 13

Ion with highest abundance + most stable fragment

Question 14

What’s happens when some molecules absorb infrared radiation?

Answer 14

Vibrations which stretches (bond length increase or decrease) or Bends (bond angle increases or decreases)

Question 15

What is linked to absorption of infrared radiation?

Answer 15

Changes in polarity of molecules. So simple non-polar molecules (H2 OR CL2) Do not absorb IR

Question 16

When does stretching occur?

Answer 16

When a bond absorbs IR and uses it to alter the length of the bond

Question 17

What is transmittance value in IS?

Answer 17

The amount of radiation absorbed at a particular wave number

Question 18

What does the wave number of an infrared absorption represent?

Answer 18

The frequency of IR absorbed by a particular bond in a molecule

Question 19

What does the intensity of an Infrared absorption describe?

Answer 19

Amount of IR absorbed.

Question 20

What is the correlation between intensity and transmittance?

Answer 20

Weak intensity = high transmittance value vice versa

Question 21

What are the 3 mains ways of using infrared spectra?

Answer 21

Predicting spectrum of organic compound

Deducing the functional group from a list of wave numbers

Deducing the structure from molecular formula and wave number