Give the reasons for the following:
(i) Iodoform is prepared by reacting acetone with hypoiodite and not with idodine. Explain.
(ii) Halogen acids readily combine with alkene to form addition products but fail to react with carbonyl compounds. Discuss.

Explanation

(i) In acetone molecule `alpha`- Hydrogen atoms are to be replaced as `H^(+)` ions by `I^(+)` ion which is made available by hypoiodite (i.e., NaOI). Iodine being non-polar in nature, does not provide `I^(+)` ion for the attack.
`CH_(3)COCH_(3) + 3IO^(-) to Cl_(3)COCH_(3)+3OH^(-)`
(ii) Halogen acids (HX) reacts with alkenes to form haloalkanes but they fall to react with the carbonyl compounds. In fact, the attack does take place but the product is unstable and decomposes to form carbonyl compound along with halogen acids. Thus reaction becomes reversible.