12th Class Chemistry Sample Paper Chemistry Sample Test Paper-2

  • question_answer   How can we enhance the reactivity of aryl halides?                                                                                                    [2] Or (i) How can you obtain iodoethane from ethanol when no other iodine containing reagent except Nal is available in the laboratory? (ii) Write a test to detect the presence of double bond in a molecule,                                                                              [1+1]

    Answer:

      Aryl halides are less reactive due to stability of (C?X) bond due to resonance effect. (ii) more electronegativity of C on which (X) is attached. (iii) instability of phenyl carbocation reaction is not possible. But reactivity of (C?X) bond can be increased by (i) using high temperature (623 K) and high pressure (300 atm).                                     [1] (ii) using electron-withdrawing group as ??CN, ?COOH in ortho and para-position. (i)         Or                                                                    [1] (ii) (a) water is decolourised by (C=C) bond. (b) Alkenes decolourise alkaline  (Baeyer's reagent)                        [1]


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