Q1(c). Diethylamine and 2-fluoro-1-acetylcyclohexene: addition–elimination

Introduction. The C=C is conjugated with C=O, so its β-carbon (C-2, bearing F) is electrophilic. A nucleophile adds there (conjugate addition) and fluoride, now on an sp³ carbon next to an enolate, is expelled. This is nucleophilic vinylic substitution by addition–elimination (AdN–E).

Scheme: Addition of the amine to the β-carbon, then loss of fluoride re-forms the C=C.

1. The nitrogen lone pair of Et₂NH attacks C-2 (Michael-type addition); the π electrons move to the enolate oxygen. This is the slow step.
2. The tetrahedral C-2 now carries F and NHEt₂⁺. The enolate pushes back to re-form C=C and F⁻ leaves; a second amine (or the fluoride) removes H⁺ from nitrogen.
3. Fluorine is a good leaving group here because C–F breaking is not rate-limiting; its strong -I effect makes C-2 more electrophilic in step 1.
4. The product is stabilised by push–pull conjugation N-C=C-C=O <→ N+=C-C=C-O⁻ (a vinylogous amide), so substitution, not simple addition, is observed.

Conclusion. Product: 1-[2-(diethylamino)cyclohex-1-en-1-yl]ethan-1-one, an enaminone (C₁₂H₂₁NO), formed by conjugate addition of Et₂NH followed by elimination of F⁻.

Application. β-Halo enones and β-chlorovinyl ketones react with amines in this way; enaminones made so are building blocks for pyrazoles, pyrimidines and quinolones.