Amines JEE Advanced previous year questions with solutions

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1. Q1JEE Advanced Adv 2008 (Paper 2)
   Statement 1 Aniline on reaction with $\mathrm{NaNO}_2 / \mathrm{HCl}$ at $0^{\circ} \mathrm{C}$ followed by coupling with $\beta$-naphthol gives a dark coloured precipitate. Statement 2 The colour of the compound formed in the reaction of aniline with $\mathrm{NaNO}_2 / \mathrm{HCl}$ at $0^{\circ} \mathrm{C}$ followed by coupling with $\beta$-naphthol is due to the extended conjugation.
   1. A.Statement 1 is true, Statement 2 is true, Statement 2 is a correct explanation for Statement 1.
   2. B.Statement 1 is true, Statement 2 is true, Statement 2 is not a correct explanation for Statement 1.
   3. C.Statement 1 is true, Statement 2 is false.
   4. D.Statement 1 is false, Statement 2 is true
   Show answer & solution

   Answer: (A)

   Statement II is correct. Statement I appears correct in the light of Statement II. What is the colour of a dye that dye is not in included in JEE syllabus but what is the cause and understanding behind a colour could be essentially expected. Concept Usually a certain proportion of the flight is absorbed and the rest reflected, the substance has the colour of the reflected light. If only a single band is absorbed, the substance has the complementary colour. - The wavelength of photon absorbed depends on the energy difference between the excited and ground states. The smaller the difference, the longer being the wavelength. - The larger the number of electrons involved in resonance, the smaller is the energy difference between the ground and excited state. Hence, the more extended the conjugation in a molecule and the greater the contribution of charged structures, the longer is the wavelength of the photon required to excite the molecule. - Especially, the presence of $+I /+M$ and $-I /-M$ groups in the conjugated system will both extend the conjugation and increase the contributions of charged structures to the resonance hybrid. Therefore, in these circumstances, the wavelength should become progressively longer. - Depending on this discussion it is apparent that the concerned resultant azodye will absorb higher wavelength. $\begin{array}{ccc}\text { Wavelength } & \text { Colour absorbed } & \text { Complimentary colour } \\ 490-500 & \text { Blue-green } & \text { Red } \\ 580-595 & \text { Yellow } & \text { Blue } \\ 605-750 & \text { Red } & \text { Blue-green }\end{array}$