Q8(c)(i). Characteristic fragment ions
1. Phthalic acid diethyl ester shows a characteristic peak at m/z 149 in the mass spectrum. Account for the observance of this peak by fragmentation pattern. 2. The mass spectrum of ethylbenzene shows a characteristic peak at m/z 91 while n-propylbenzene shows a strong peak at m/z 92. Explain with the help of fragmentation pattern.
Answer in brief
Diethyl phthalate gives m/z 149, protonated phthalic anhydride (base peak); ethylbenzene gives m/z 91 by benzylic cleavage and n-propylbenzene m/z 92 by McLafferty rearrangement.
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Coversdiethyl phthalate m/z 149tropylium ionbenzylic cleavageMcLafferty rearrangementmass spectrometry
All parts of Question 8
- 8(a)(i) Coupling constants of the lettered protons5 marks
- 8(a)(ii) Chemical shifts of Hᵃ and Hᵇ5 marks
- 8(a)(iii) Number of ¹H NMR signals5 marks
- 8(b)(i) Structure of the halogenated ester10 marks
- 8(b)(ii) C₆H₁₂ alkenes with peaks at m/z 42 and 565 marks
- 8(c)(i) Characteristic fragment ions10 marks
- 8(c)(ii) Structure of C₄H₅NO₂10 marks