Cyclopentanone tautomers

Condensation of [3- or "y-amino alcohols with aldehydes or ketones RR CO gives the product 27. In solution the position of the equilibrium varies with R and R, and with the solvent (73). When the carbonyl reactant is a substituted benzaldehyde, the solid is found (IR, KBr) to comprise molecules of the open-chain structure 27a, whereas aliphatic aldehydes and ketones give crystals of dihydro- 1,3-benzoxazines, 27b. An interesting case is that of the condensation product of o-hydroxybenzylamine with cyclopentanone, for which McDonagh and Smith (73) suggest that ring and chain tautomers coexist in the solid. 

The steric influence on the enamine-imine tautomerism has also been observed in the cyclic ketone derivatives. Cyclohexanone imines of w-propylamine, cyclohexylamine and 2-bornylamine show no signals ascribed to the enamine tautomer in their NMR spectra, but the /-butylamine38 does display signals of the enamine. In DMSO-d6 it comprises 38% of enamine 56 at equilibrium. The proportion of the 3,3,5,5-tetra-methylcyclohexanone and cyclopentanone enamines 57 and 58 is even higher, rising to 52% and 58%, respectively, in DMSO-d663. 

Draw a stepwise mechanism for the conversion of cyclopentanone (A) to its enol tautomer (B) in the presence of acid. 

Draw structuroa for the enol tautomers of the following compounds (a) Cyclopentanone (b) Acetyl chloride (c) Ethyl acetate... 

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