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Question:

Lucas test is given by an alcohol within 5 minutes. 0.22 g of which liberates 56 mL of CH4 at STP on treating with CH3MgI. The structure of alcohol is:

CH3−C(OH)H−CH3

(CH3)3C−C(OH)H−CH3

CH3−CH2−C(OH)H−CH3

(CH3)2CH−C(OH)H−CH3

Solution:

The correct option is B (CH3)2CH−C(OH)H−CH3
Lucas test will be given by all given alcohols within 5 minutes as all are 2° alcohols. Exact structure can be known by molecular mass or formula of alcohol which will be obtained as follows:
Let molecular mass of alcohol be M.
56/22400 = 0.22/M
or, 22400 × 0.22/56 = 88
The general formula of alcohols is CnH2n+1OH.
The molecular mass 88 corresponds to the value of n=5.
Thus, the 2° alcohol is (CH3)2CHCH(OH)CH3