91Ó°ÊÓ

When cyclohexanone is heated in the presence of a large amount of acetone cyanohydrin and a small amount of base, cyclohexanone cyanohydrin and acetone are formed. Propose a mechanism.

Paraldehyde, a sedative, and hypnotic agent, is prepared by treatment of acetaldehyde with an acidic catalyst. Propose a mechanism for the reaction.

The Meerwein–Ponndorf–Verley reaction involves the reduction of a ketone by treatment with an excess of aluminum triisopropoxide,${\left[{\left({\mathbf{CH}}_3\right)}_2\mathbf{CHO}\right]}_3\mathbf{Al}$.The mechanism of the process is closely related to the Cannizzaro reaction in that a hydride ion acts as a leaving group. Propose a mechanism.

Propose a mechanism to account for the formation of 3,5-dimethyl pyrazole from hydrazine and 2,4-pentanedione. Look carefully to see what has happened to each carbonyl carbon in going from starting material to product.

In light of your answer to Problem 19-46, propose a mechanism for the formation of 3, 5-dimethylisoxazole from hydroxylamine and 2,4-pentanedione

Trans alkenes are converted into their cis isomers and vice versa on epoxidation followed by treatment of the epoxide with triphenylphosphine.Propose a mechanism for the $\mathbf{epoxide}→\mathbf{alkene}$reaction.

Treatment of an $\mathrm{Î\pm },\mathrm{β}$-unsaturated ketone with basic aqueous hydrogen peroxide yields an epoxy ketone. The reaction is specific to unsaturated ketones; isolated alkene double bonds do not react. Propose a mechanism.

How would you carry out the following reactions? More than one step may be

required.

(a) 3-Hexyne3-Hexanone

(b) Benzenem-Bromoacetophenone

(c) BromobenzeneAcetophenone

(d) 1-Methylcyclohexene2-Methylcyclohexanone

Primary amines react with esters to yield amides: RCO₂R^' + R^"NH₂ $→$RCONHR^" + R^'OH . Propose a mechanism for the following reaction of an a b-unsaturated ester.

When crystals of pure $\mathrm{Î\pm }$-glucose are dissolved in water, isomerization occurs slowly to produce $\mathrm{β}$-glucose. Propose a mechanism for isomerization.