>> Study Material
>> IIT JEE Chemistry
>> Organic Chemistry
>> Carbohydrates Amino Acids and Peptides
>> Solved Problems on Organic Chemistry
Board Types Questions
Prob 1. In E. coli DNA, the AT/GC ratio is 0.93. If the number of moles of adenine in the DNA sample is 558,000, calculate the number of moles of guanine present
Sol. Number of moles of adenine must be equal to that of thymine
(A + T) = 558,000 + 558,000 = 1116000
Since (A + T)/(C + G ) = 0.93
Therefore, no of moles of C + G
C + G = 1116000/0.93 = 1200000
Since number of moles of C = number of moles of G
Number of moles of guanine =1200000/2 = 600000
Prob 2. How will you synthesize alanine from acetylene?
Prob 3. Write the structure of alanine at pH =2 and pH = 10.
Sol. Amino acids exist as zwitter ions (I) in aqueous solution. In presence of acids (pH=2) basic COO– accepts a proton to give cation (II) but in presence of base (pH = 10), the acidic donates a proton to the base and thus exists as anion (III).
Prob 4. Glycine exists as (H3N+CH2COO–) while anthranilic acid (P–NH2C6H4– COOH) does not exist as dipolar ions.
Sol. – COOH is too weakly acidic to transfer H+ to the weakly basic – NH2 attached to the electron withdrawing benzene ring. When attached to an aliphatic carbon, the – NH2 is sufficiently basic to accept H+ from – COOH group
Sol. A = (NH4)2S2O8
Prob 6. Complete the following reaction:
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)
(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?
Prob 9. Complete the following reactions
Prob 11. Give the classification of polymers obtained from esters of acrylic acid
(CH2 = CH.COOH)
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 SN2 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.
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 -anomer of given mono saccharide is + 112° and for
-anomer is + 19°. Specific rotation of equilibrium mixture is 52.7° calculate % composition of α and β anomers in the equilibrium mixture.
Sol. Suppose fraction of and anomers 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+CH2COOH