Q6(f). Norrish Type II reaction of two aryl alkyl ketones
Providing suitable mechanism, write down the product(s) in the following reaction: aryl alkyl ketone, hν → ? Compare the product(s) pattern formation when (i) R′ = R″ = H; (ii) R′ = R″ = CH₃. [structure of the ketone PhCOCH₂CH₂CHR′R″ given in the paper]
Answer in brief
Norrish Type II cleavage in both: (i) acetophenone + ethene; (ii) acetophenone + 2-methylpropene, the tertiary γ-H being abstracted faster; a cyclobutanol is the minor product in each case.
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CoversNorrish Type IIphotochemistry of ketonesγ-hydrogen abstraction1,4-biradicalNorrish–Yang cyclisation
All parts of Question 6
- 6(a) Reactivity of four alkenes towards electrophilic addition4 marks
- 6(b) Quaternisation, then Sommelet–Hauser rearrangement4 marks
- 6(c) Woodward–Fieser rules: three dienones4 marks
- 6(d) Carbonyl stretching bands of three lactones4 marks
- 6(e) Epoxidation of cholesterol with a peroxy acid4 marks
- 6(f) Norrish Type II reaction of two aryl alkyl ketones6 marks
- 6(g) Three isomeric esters C₄H₈O₂ from ¹H NMR6 marks
- 6(h) McLafferty rearrangement in a ketone, an acid and an ester6 marks
- 6(i) Stretching frequencies of six single bonds2 marks