Consider the following reactions $$\mathrm{A} \xrightarrow[\text { (ii) } \mathrm{H}_{3} \mathrm{O}^{+}]{\text {(i) } \mathrm{CH}_{3} \mathrm{MgBr}} \mathrm{~B} \xrightarrow[573 \mathrm{~K}]{\mathrm{Cu}} \text { 2-methyl-2-butene }$$ The mass percentage of carbon in A is ____.

JEE Main · 2020 · 09 Jan 2020 · Shift 2 · Alcohols Phenols and Ethers

Consider the following reactions

A (i) CH_{3} MgBr (ii) H_{3} O^{+} B Cu 573 K 2-methyl-2-butene

The mass percentage of carbon in A is ____.

Answer: 66.67

Solution

The product 2-methyl-2-butene comes from dehydrogenation of an alcohol B over copper at

573 K

, so B is 2-methylbutan-2-ol. That tertiary alcohol is built by adding methylmagnesium bromide to a carbonyl, and since the Grignard supplies one carbon, A must carry the remaining four carbons as butan-2-one,

C H_{3} COC H_{2} C H_{3}

(

C_{4} H_{8} O

, molar mass

72 g/mol

). The mass percentage of carbon in A is

\frac{4 \times 12}{72} \times 100 = 66.67%

JEE Main · 2020 · 09 Jan 2020 · Shift 2 · Numerical answer

Practise more: all JEE Main PYQs on Alcohols Phenols and Ethers →

More JEE Main questions on Alcohols Phenols and Ethers

Given below are two statements :

Statement I: Phenol on treatment with $CHCl_{3} /$ aq. KOH under refluxing condition, followed by acidification produces $p$ -hydroxy benzladehyde as the major product and $o$ -hydroxy benzaldehyde as the minor product.

Statement II …
JEE Main 2026View solution →
3,3-Dimethyl-2-butanol cannot be prepared by:
A.
B.
C.
D.
E.
Choose the correct answer from the options given below:
JEE Main 2026View solution →
A mixed ether ( P ), when heated with excess of hot concentrated hydrogen iodide produces two different alkyl iodides which when treated with aq. NaOH give compounds (Q) and (R). Both (Q) and (R) give yellow precipitate with NaOI. Identify the mixed ether (P):
JEE Main 2026View solution →
Consider the following two reactions A and B .
(A) (see structure)
(B) (see structure)

Numerical value of [molar mass of $x +$ molar mass of y ] is ______。
JEE Main 2026View solution →
From the following, how many compounds contain at least one secondary alcohol?
JEE Main 2026View solution →
Consider the following reaction sequence

vapour density 47]
Compound (y) develops characteristic colour with neutral $FeCl_{3}$ solution.
Identify the INCORRECT statement from the following for the above sequence.
JEE Main 2026View solution →