Edexcel A Level Chemistry:复习笔记7.7.1 Mass Spectrometry

Category: A-level课程, 教材笔记, 福利干货 Date: 2022年9月23日上午10:40

At AS level, you have used mass spectrometry to determine:
- Relative atomic mass from isotopic abundance
- Possible molecular formulae from molecular ion peaks
- Organic structures from fragmentation patterns
High resolution mass spectrometry can be used to deduce / confirm molecular formulae
High resolution mass spectrometers provide data accurate to four, or sometimes more, decimal places
This means that a compounds molecular formula can sometimes be deduced by using atomic masses accurate to four decimal places

Table of selected accurate relative atomic masses

A compound is found to have an Mr value of 58.0417.

Determine if the compound is:

Answer

High resolution mass spectrometry can inform you about the molecular formula, it cannot tell you about the actual structure
- In the worked example above, the final answer was C3H6O but you cannot say whether this is propanal or propanone
- You would have to use the fragments on the mass spectrum for further detail that might help deduce more information about the structure
Sometimes you may calculate the molecular mass of a compound and it won't match the value given in the question exactly
- In this case, you should:
  - Firstly, double check your calculation(s)
  - Secondly, choose the compound that is the closest

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