BRAINCAKERacemates from Nucleophilic Addition
Aldehydes and ketones react with hydrogen cyanide by nucleophilic addition to form hydroxynitriles. The reaction uses HCN in the presence of KCN, which provides the CN− nucleophile. In practice KCN is used with a little dilute acid, because HCN itself is a very toxic gas.
Mechanism (ethanal + HCN → 2-hydroxypropanenitrile):
1. The C=O bond is polar, so the carbonyl carbon is δ+. The CN− ion uses the lone pair on its carbon to attack the δ+ carbon, and the π bond breaks, moving a pair of electrons onto the oxygen.
2. The negatively charged intermediate takes an H+ ion from HCN (or from the acid), forming the OH group.
Sign in free to see the rest of this lesson, the R.E.C.I.P.E. recall steps and the quiz
BrainCake is free. Make an account in seconds and pick up where this page stops.
Key terms in this lesson
- nucleophilic addition
- A reaction mechanism in which a nucleophile adds across a polar double bond, such as the C=O of a carbonyl group.
- hydroxynitrile
- A compound containing both a hydroxyl (OH) group and a nitrile (CN) group, formed when hydrogen cyanide adds to a carbonyl compound.
- nucleophile
- An electron-pair donor that is attracted to a region of positive charge and forms a new covalent bond there.
More in Chirality
All 6 lessons in Chirality · All Edexcel A-level Chemistry topics