CBSE Class 12 Chemistry Notes: Biomolecules – Important Question for JEE

Prob 6.  Complete the following reaction:

Sol.

Prob 7. In the structure of aspartame (an artificial sweetner) which is a peptide

i)  Identify the four functional groups

(ii) Write the zwitterionic structure

(iii) Write the structure of amino acids obtained from the hydrolysis of aspartame

Sol.  (i)   Four functional groups in aspartame are

– NH₂ (amino group)

– COOH (carboxyl group)

(ii)

(iii) Hydrolysis of aspartame gives following two amino acids

Prob 8.       Following two amino acids lysine and glutamine form dipeptide linkage. What are two possible dipeptide?

Sol.

Prob 9. Complete the following reactions

Sol.

Prob 10.

Sol.

Prob 11.     Give the classification of polymers obtained from esters of acrylic acid  (CH₂ = CH.COOH)

Sol.

Formula of monomer	Polymer	Characteristics	Uses
		Hard transparent, high optical clarity. It is capable of acquiring different colours and tints	Lenses, transparent object domes and skylights plastic jewellery
		Tough and rubbery polymer	Similar to above
		Hard, horney and high melting material	Used in preparing cloth, carpets and blankets

 

Prob 12.  When primary bromides are treated with a solution of NaI in pure acetone precipitate generates within 3 minutes at 25°C whereas primary chlorides when treated with same reagent precipitate generates within 6 minutes at 50°C. Explain.

 

Sol.The reaction is probably of the S_N2 type involving a bimolecular attack of the iodide ion upon the carbon atom carrying the chloride or bromine. Now Br^– is better leaving group when Cl^– (as it is a weaker base). So the rate of the reaction for bromides is faster.

RBr + NaI -> RI + NaBr|

RCl + NaI -> RI + NaCl|

 

Prob 13. Glucose and fructose give the same osazone? Explain

 Sol. During osazone formation reaction occurs only at C₁and C₂ while rest of the molecule remains same, and glucose & fructose differ from each other only in arrangement of atoms at C₁ and C₂, so they give same osazone

Prob 14. Specific rotations of α-anomer of given mono saccharide is + 112^o and for  β-anomer is + 19^o. Specific rotation of equilibrium mixture is 52.7^o calculate % composition of  α and  β anomers in the equilibrium mixture.

Sol. Suppose fraction of andanomers is X and Y respectively

X + Y = 1 ……………………..(1)

112X + 19Y = 52.7……………(2)

By solving above two equations

X = 36.2%,   Y = 63.8%

 

Prob 15. Predict the products of the treatment of glycine with

(a)  Aqueous NaOH

(b)  Aqueous HCl

(c)  Acetic anhydride

(d)  NaNO₂ + HCl

 

Sol.  (a)  H₂N.CH₂COO^–Na⁺

(b)  Cl^– + H₃N^ÅCH₂COOH

(c)

(d) HOCH₂COOH + N₂

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