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>> Chemistry Mains-2001
Time : Two hours Max. Marks : 100
1. Compound (X) on reduction with LiAIH4 gives a hydride (Y) containing 21.72 hydrogen along with other products. The compounds (Y) reacts with air explosively resulting in boron trioxide. Identify (X) and (Y). Give balanced reactions involved in the formation of (Y) and its reacton with air. Draw the structure of (Y).
2. A metal complex having compositon Cr (NH3)4 CI2Br has been isolated in two forms (A) and (B). The form (A) reacts with AgNO3 to give a white precipitate readily soluble in dilute aqueous ammonia, whereas (B) givens a pale yellow precipitate soluble in concentrated ammonia. Write the formula of (A) and (B) and state the hybridization of chromium in each. Calculate their magnetic moments (spin-only value).
3. Starting from SiCI4, prepare the following in steps not exceeding the number given in parentheses (give reactions only):
(i) Silicon (1)
(ii) Linear silicone containing methyl groups only (4)
(iii) Na2SiO3 (3)
4. Hydrogen peroxide solution (20 ml) reacts quantitatively with a solution of KMnO4(20 ml) acidified with dilute H2SO4. The same volume of the KMnO4 solution is just decolourised by 10 mL of MnSO4 in neutral medium simultaneously forming a dark brown precipitate of hydrated MnO2. The brown precipitate is dissolved in 10 ml of 0.2 M sodium oxalate under boiling condition in the presence of dilute H2SO4. Write the balanced equations involved in the reactions and calculate the molarity of H2O2.
5. How would you synthesise 4-methoxyphenol from bromobenzene in NOT more than five steps? State clearly the reagents used in each step and show the structures of the intermediate compounds in your synthetic scheme.
6. Cyclobutyl bromide on treatment with magnesium in dry ether forms an organometallic (A). The organometallic reacts with ehtanal to give an alcohol (B) after mid acidification. Prolonged treatment of alcohol (B) with an equivalent amount of HBr gives 1-bromo-1-methylcyclopentane (C). Write the structures of (A), (B) and explain how (C) is obtained from (B).
7. Aspartame, an artificial sweetener, is a peptide and has the following structure:
(i) Identify the four functional groups.
(ii) Write the zwitterionic structure.
(iii) Write the structures of the amino acids obtained from the hydrolysis of aspartame.
(iv) Which of the two amino acids is more hydrophobic?
8. An alkene (A) C16H16 on ozonolysis gives only one product (B) C8H8O. Compound (B) on reaction with NaOH/I2 yields sodium benzoate. Compound (B) reacts with KOH/NH2NH2 yielding a hydrocarbon (C) C8H10. Write the structures of compounds (B) and (C). Based on this information two isomeric structures can be proposed for alkene (A). Write their structures and identify the isomer which on catalytic hydrogenation (H2/Pd – C) gives a racemic mixture.
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