JEE Main 2021 · Chemistry · Carbonyl Compounds, Carboxylic Acids and Amines · easy

Benzaldehyde is treated with half its molar amount of acetone in the presence of dilute NaOH with heating, so that both α-positions of acetone…

Numerical answer

Benzaldehyde is treated with half its molar amount of acetone in the presence of dilute NaOH with heating, so that both

\alpha

-positions of acetone condense. The number of

sp^2

-hybridised carbon atoms in one molecule of the product is

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Answer: 17

Two moles of

\mathrm{C_6H_5CHO}

react with one mole of acetone by Claisen-Schmidt condensation, losing two

\mathrm{H_2O}

to give dibenzalacetone (1,5-diphenylpenta-1,4-dien-3-one),

\mathrm{C_6H_5CH=CH-CO-CH=CH-C_6H_5}

, formula

\mathrm{C_{17}H_{14}O}

. All carbons are

sp^2

12

aromatic carbons,

4

alkene carbons and

1

carbonyl carbon. Total

=12+4+1=17

; there are no

sp^3

carbons because the

\mathrm{CH_3}

groups of acetone have both been converted into

=\mathrm{CH}

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