OCR A · AS / Year 12
OCR A Organic Mass Spectrum Questions
Calculate molecular-ion and fragment-ion masses, balance stated fragment formulae and combine mass-spectrum evidence with IR. No fragment-structure drawings are assessed.
Work it out, then check
Question 1 of 6
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Worked answer
Before the next question
In electron impact, a molecule loses an electron to form a positive molecular radical ion. A stated neutral loss lets you calculate the remaining fragment mass and atom inventory. A single peak alone does not prove a unique molecular structure. These formula tasks prepare for, but do not assess, the OCR fragment drawings.
A worked example
The propanone molecular ion has nominal m/z 58. Loss of CH₃• (mass 15) gives CH₃CO⁺ at m/z 43: [C₃H₆O]⁺• → CH₃CO⁺ + CH₃•.