Q6(i). Acetone: solvent shift of the n → π* band
Acetone absorbs at 279 nm in hexane whereas the value of λmax in water is 264.5 nm. Provide a suitable justification to your answer.
Answer in brief
The band is the n → π* transition; water hydrogen-bonds to the oxygen lone pair and lowers the n level, so the energy gap is larger: blue (hypsochromic) shift of 14.5 nm.
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Coversn→π* transitionhypsochromic shiftblue shiftsolvent effect UVacetone UV spectrum
All parts of Question 6
- 6(a) Chlorocarbene from CH₂Cl₂; ring expansion of 3-methylindole4 marks
- 6(b) Ozonolysis of camphene, then Wolff–Kishner reduction4 marks
- 6(c) Reductive amination, then intramolecular aza-Michael addition4 marks
- 6(d) Benzaldehyde and ethane-1,2-dithiol: a 1,3-dithiolane4 marks
- 6(e) Amidomercuration–demercuration of hex-1-ene in acetonitrile4 marks
- 6(f) Dimerisation of cyclopentadiene: endo rule by frontier orbitals4 marks
- 6(g) Two isomeric esters C₇H₁₄O₂ from ¹H NMR4 marks
- 6(h) Mass spectrum of 3-butyn-2-ol: the ion of m/z 554 marks
- 6(i) Acetone: solvent shift of the n → π* band4 marks
- 6(j) Butyrophenone: McLafferty rearrangement and α-cleavage4 marks