Chapter 137 of 2363 min read

Preparation and reactions of alcohols

Why this is asked: The Lucas test tells 1°, 2° and 3° alcohols apart by how fast turbidity appears with ZnCl₂/HCl — instantly for 3° (via a stable carbocation), within minutes for 2°, not at all at room temperature for 1°. Acidity among simple alcohols runs 1° > 2° > 3°, the opposite of carbocation stability, because the same electron-donating alkyl groups that stabilise a cation destabilise the alkoxide anion instead.

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Test yourself

•The products A and B obtained in the following reactions, respectively, are: $3ROH + PC l_{3} \to 3RCl + A$ $ROH + PC l_{5} \to RCl + HCl + B$
•Which one of the following alcohols (three drawn as structures; the fourth is $C H_{3} C H_{2} C H_{2} C H_{2} OH$ ) reacts instantaneously with Lucas reagent?
•Identify the correct reagents that would bring about the transformation shown in the figure.

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