JEE Main · 2021 · 17 Mar 2021 · Shift 2 · Chemical Bonding and Molecular Structure

Mesityl oxide is 4-methylpent-3-en-2-one, $(\mathrm{C}{\mathrm{H}}_3{)}_2\mathrm{C}=\mathrm{CH}-\mathrm{CO}-\mathrm{C}{\mathrm{H}}_3$. Its six carbon atoms are joined by five carbon-carbon linkages: two from the gem-dimethyl carbon to its two methyl groups, the double bond from that carbon to the adjacent methine carbon, the single bond from the methine carbon to the carbonyl carbon, and the single bond from the carbonyl carbon to the terminal methyl group. A double bond is made of one sigma and one pi component, so every one of these five linkages supplies exactly one sigma bond. The total number of carbon-carbon sigma bonds is $5$.