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Chemistry · 2026 · 5 marks
Haloalkanes and HaloarenesChemical Reactions of Haloalkanes and Haloarenes5 marksUnderstandlong answer
CBSE 2026 · Region 5 · Set 1 · Q33
(a) (i) (I) Which of the following is more reactive towards S_N 1 reaction: 2-Bromo-2-methylbutane or 1-Bromopentane (II) What type of halide is…
(i)
(I)
Which of the following is more reactive towards $\displaystyle \mathrm{S}_{\mathrm{N}} 1$ reaction : $\displaystyle 2$-Bromo-$\displaystyle 2$-methylbutane or $\displaystyle 1$-Bromopentane
(II)
What type of halide is present in the following compound :
(III)
Why is chloroform stored in dark coloured bottles ?
(ii)
Define the following terms :
(I)
Ambident Nucleophiles
(II)
Racemic mixture
(i)
Answer the following :
(I)
Which isomer of $\displaystyle \mathrm{C}_{4} \mathrm{H}_{9} \mathrm{Br}$ is most reactive towards $\displaystyle \mathrm{S}_{\mathrm{N}} 1$ reaction?
(II)
Predict the alkene that would be formed by dehydrohalogenation of $\displaystyle 1$-Bromo-$\displaystyle 1$-methylcyclohexane.
(III)
Although chlorine shows strong - I effect, yet it is ortho/para-directing in electrophilic aromatic substitution reactions. Why ?
(ii)
Write the major product in the following reactions :
(I)
(II)
Marking-scheme solution
(i)
(I)
$\displaystyle 2$-Bromo-$\displaystyle 2$-methylbutane
(II)
Vinylic halide
(III)
It is slowly oxidised in presence of light to give poisonous gas
phosgene/
2CHCl3 + O2 $\displaystyle \xrightarrow{\text{light}}$ 2COCl2 + 2HCl
(ii)
(I)
Groups having two nucleophilic centres.
(II)
Equal amounts of dextro and laevo enantiomers in a mixture.
(i)
(I)
Tert-butyl bromide / (CH3)3C−Br / $\displaystyle 2$-Bromo-$\displaystyle 2$-methylpropane
(II)
or
(III)
Because +R effect stabilises the intermediate carbocation.
(ii)
(I)
(II)
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CBSE Class 12 Chemistry past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.