Q9(c). Beer’s law for camphor; λmax of the methyl halides
(i) What is the concentration value for a solution of camphor (εmax = 14) in hexane solution in a 10 cm cell? A at 295 nm was found to be 2.52. (ii) Offer your explanation for the variation of λmax values for the following compounds: methyl chloride (λmax = 173 nm), methyl bromide (λmax = 204 nm), methyl iodide (λmax = 258 nm).
Answer in brief
(i) c = 0.018 mol L⁻¹ (1.8 × 10⁻² M). (ii) The band is n → σ* of C–X; from Cl to I the n level rises and σ* falls, so λmax increases.
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CoversBeer–Lambert lawn → σ* transitionn → π* transitionalkyl halidesUV spectroscopybathochromic shift
All parts of Question 9
- 9(a) Structure from UV, IR, NMR and mass data: C₇H₈BrN10 marks
- 9(b) Dieckmann condensation, then hydrolysis and decarboxylation5 marks
- 9(c) Beer’s law for camphor; λmax of the methyl halides5 marks
- 9(d)(i) Birch reduction with ring closure: a spiro acid5 marks
- 9(d)(ii) Robinson annulation to a spiro enone5 marks