Define ambident nucleophile with an example.

The nucleophiles that can attack through two different sites are known as ambident nucleophiles . For ex :- CN - , NO 2 - , - O - CH = S A cyanide ion can attack through either C atom or N atom to form alkyl cyanide or alkyl isocyanide.

Identify the chiral molecule in the following pair:

For a molecule to be chiral it must have a non-superimposable mirror image. For this, an asymmetric carbon atom (an atom attached to four different atoms or group of atoms) must be present in the molecule. The '*' carbon is asymmetric, therefore, molecule (i) is a chiral molecule.

Predict the major product formed when 2-Bromopentane reacts with alcoholic KOH .

When 2-Bromopentane is treated with an alcoholic KOH nucleophilic substitution reaction takes place and pent-2-ene, pent-1-ene are formed. Pent-2-ene is major product also known as Saytzeff's product, and it is more stable alkene. This reaction involves elimination of β -hydrogen and hence this reaction is called β -elimination reaction.

Give one use of CHI 3 .

CHI 3 is prepared industrially by the electrolysis of an aqueous solution of ethanol or acetone containing sodium carbonate and potassium iodide. It is used as an antiseptic. Its antiseptic properties are due to the liberation of free iodine.

Name the instrument used for measuring the angle by which the plane polarised light is rotated.

Polarimeter is the instrument used for measuring the angle by which the plane polarised light is rotated. Polarimeter consists of a source of monochromatic light, two Nicol prisms and a tube. One Nicol prism is called polariser and the other is called analyser.

Predict the stereochemistry of the product formed if an optically active alkyl halide undergoes substitution reaction by S N 1 mechanism.

In S N 1 mechanism, there are two steps. The first involves the formation of intermediate carbocation by heterolysis of tertiary compound. This intermediate carbocation contains sp 2 hybridized carbon atom and thus it is planar. In the second step carbocation is attacked by the nucleophile from either side of R + so that a racemic mixture is formed in which the optical activity due to one is opposite of the other. Hence, an optically inactive product is formed when an optically active alkyl halide undergoes substitution reaction by S N 1 mechanism.

Account for the following : t-Butyl chloride on heating with sodium methoxide gives 2-methylpropene instead of t-butylmethylether.

Tertiary alkyl halides on heating with sodium methoxide undergo elimination reaction to yield an alkene as major product. Since, t-butyl chloride is a tertiary halide, the nucleophilic substitution reaction is not possible at the crowded centre. Hence, t-butyl chloride on heating with sodium methoxide gives 2-methylpropene instead of t-butylmethylether.

Write the structure of the alkene formed by dehydrohalogenation of 1 - bromo - 1 - methylcyclohexane with alcoholic KOH .

Dehydrohalogenation of a haloalkane results in the production of an alkene. In general, secondary and tertiary haloalkanes undergo dehydrohalogenation reactions using a strong base in a polar solvent (such as ethanol, EtOH ) at higher temperature (usually heated under reflux). The dehydrohalogenation of 1 - bromo - 1 - methylcyclohexane with alcoholic KOH produces 1 - methylcyclohexene. .

E M B I B E

EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter -1 - Haloalkanes and Haloarenes>CBSE-2018>Q 1

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12th CBSE

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Out of chlorobenzene and benzyl chloride, which one gets easily hydrolysed by aqueous $NaOH$ and why?

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