Test: Diols & Polyols - NEET MCQ

A slightly weaker base (NaHCO₃) is used in the second step S_N2 reaction otherwise oxirane formation would be preferred.

Epoxide, upon hydrolysis in either acidic or alkaline medium gives anti, vicinal diol.

Greater the number of hydroxy groups, greater the solubility in water. Between (II) and (III), (III) is slightly less soluble due to greater hydrophobic alkyl fraction.

At planar carbonyl carbons, hydride ion attacks from both sides giving both stereomers. Hence, the product diols would be all stereomers of 2, 3 - butanediol.

(d) PI₃ does not form di iodide with vicinal diols.

Both oxirane hydrolysis and halide substitution (S_N2) take place.

Ethylene glycol on heating with concentrated H₂SO₄ gives 1 , 4-dioxane

(a) Alkaline KMnO₄ gives syn, vicinal diol with alkene.
(b) Here, oxirane is formed as the major product.
(c) Epoxidation followed by hydrolysis gives diol.
(d) Dihalide formed in the first step undergoes S_N2 reaction with NaHCO₃ giving diol.

(a) Vicinal diols, on heating with concentrated H₂SO₄ gives dioxane as the major product.



(d) Diols do not give dioxane in alkaline medium.

Syn vicinal diols undergo oxidative cle avage with HIO₄ giving diols, Option (b) and option (c) are anti diol and have restricted rotation.

It is a Pinacol-pinacolone rearrangement.

(I) on deprotonation gives (a) while (II) on deprotonation gives (b).

Pinacol-pinacolone rearrangemen

Deprotonation of (I) gives (a) while deprotonation of (II) gives (c).

Vicinal diols which is not tertiary, prefer to form dioxane while tertiary diols prefer to undergo Pinacol-pinacolone rearrangement.

The diol is not tertiary, hence more likely to form dioxane.

Vicinal diols which is not tertiary, prefer to form dioxane while tertiary diols prefer to undergo Pinacol-pinacolone rearrangement.
It is tertiary diol, undergo Pinacol-pinacolone rearrangeme.

Vicinal diols which is not tertiary, prefer to form dioxane while tertiary diols prefer to undergo Pinacol-pinacolone rearrangement.

(i) It is a symmetrical, 3° diol, gives (CH₃)₂CO with HIO₄, a single pinacolone (CH₃)₃C —COCH₃ and a single cyclic a mine :

(ii) With HIO₄ gives (CH₃)2CO and (C₆H₅)₂CO. (ii) is unsymmetrical, 3° diol, gives more than one pinacolone in rearrangement reaction. However it gives a single cyclic amine.

(iii) with HIO₄ gives a single ketone-acetophenone. It gives two different pinacolone in rearrangement reaction.

(iv) It is unsymmetrical, 3° diol, gives two different ketones with HIO₄ and more than one pinacolone in rearrangement reaction.