In nucleophilic addition to a carbonyl group, the carbon atom changes hybridisation from

  • A. sp3 to sp2
  • B. sp to sp2
  • C. sp2 to sp3
  • D. sp3 to sp

Explanation

The carbonyl carbon starts as trigonal planar sp2 with a bond angle of 120 degrees, and when the nucleophile adds it acquires a fourth group and becomes tetrahedral sp3 with angles near 109.5 degrees. This geometrical change is why bulky groups around the carbonyl slow the reaction down so much. Elimination reactions run the same change in reverse.

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