Question

Alkyl iodides develop colouration on long standing particularly in light. Explain.

Answer 1

This is because of spontaneous breakdown in case of iodides and bromides which have a lower bond-dissociation enthalpy as compared to fluorides and chlorides. This low enthalpy means that even at normal temperature or on exposure to sunlight, the halides (iodides and bromides) decompose to a certain extent forming free iodine and bromine, both of which are coloured and hence impart colour to the original halides.

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Answer 2

Explanation:

this is due to the spontaneous breaksown in the case of iodides and bromides,which have a lower bond dissociation enthaphy as compared to flourides and chlorides