PUC Science 2nd PUC Class 12 - Karnataka Board PUC Question Bank Solutions

Predict the products formed when cyclohexanecarbaldehyde reacts with the following reagents.

Semicarbazide and weak acid

Predict the products formed when cyclohexanecarbaldehyde reacts with the following reagents.

Excess ethanol and acid

Acetaldehyde, Acetone, Di-tert-butyl ketone, Methyl tert-butyl ketone (reactivity towards HCN)

How will you bring about the following conversion in not more than two steps?

Bromobenzene to 1-Phenylethanol

Give plausible explanation for the following:

Cyclohexanone forms cyanohydrin in good yield but 2, 2, 6 trimethylcyclohexanone does not.

Give plausible explanation for the following:

There are two −NH₂ groups in semicarbazide. However, only one is involved in the formation of semicarbazones.

Complete the synthesis by giving missing starting material, reagent or product.

\[\ce{C6H5CHO ->[H2NCONHNH2]}\]

Complete the synthesis by giving missing starting material, reagent or product.

Ortho and para nitrophenols are more acidic than phenol. Draw the resonance structures of the corresponding phenoxide ions.

Show how will you synthesize pentan-1-ol using a suitable alkyl halide.

Give the equation of the following reaction:

Oxidation of propan-1-ol with alkaline KMnO₄ solution.

Give the equation of the following reaction: 

Dilute HNO₃ with phenol.

Give the equation of the following reaction: 

Treating phenol with chloroform in the presence of aqueous NaOH.

Write the mechanism of acid-catalysed dehydration of ethanol to yield ethene.

Name the reagent used in the following reaction:

Oxidation of a primary alcohol to carboxylic acid.

Name the reagent used in the following reaction:

Oxidation of a primary alcohol to aldehyde.

Name the reagent used in the following reaction:

Benzyl alcohol to benzoic acid.

When 3-methylbutan-2-ol is treated with HBr, the following reaction takes place:

\[\begin{array}{cc}
\phantom{.......................}\ce{Br}\\
\phantom{......................}|\\
\ce{CH3 - CH - CH - CH3 ->[HBr] CH3 - C - CH2 - CH3}\\
\phantom{.}|\phantom{......}|\phantom{......................}|\phantom{........}\\
\phantom{}\ce{CH3}\phantom{...}\ce{OH}\phantom{...................}\ce{CH3}\phantom{.....}
\end{array}\]

Give a mechanism for this reaction.

(Hint: The secondary carbocation formed in step II rearranges to a more

stable tertiary carbocation by a hydride ion shift from 3rd carbon atom.)

Predict all the alkenes that would be formed by dehydrohalogenation of the following halide with sodium ethoxide in ethanol and identify the major alkene:

1-Bromo-1-methylcyclohexane

Predict all the alkenes that would be formed by dehydrohalogenation of the following halide with sodium ethoxide in ethanol and identify the major alkene:

2-Chloro-2-methylbutane