Q5(f). λmax of CH₃Cl, CH₃Br, CH₃I: n→σ*
Explain the following variations in λmax (in nm) of CH₃Cl (173), CH₃Br (204), CH₃I (258).
Answer in brief
The n→σ* energy gap decreases from Cl to I because the lone pair rises and the C–X σ* falls; hence λmax: CH₃Cl 173 < CH₃Br 204 < CH₃I 258 nm . CH₃I (258 nm) lies well inside the ordinary UV; CH₃Br (204 nm) is at its edge; CH₃Cl (173 nm) is in the vacuum UV.
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Coversn→σ* transitionlone-pair
All parts of Question 5
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