Question

Question 12.9 Which of the two: O2NCH2CH2O– or CH3CH2O– is expected to be more stable and why?

Class XI Organic Chemistry : Some Basic Principles and Techniques Page 362

Answer 1

concept :- stability of carboanions depends on the presence of electron withdrawing group. stability of carboanions is increase in the presence of electron withdrawing group while  decrease in the presence of electron releasing group. 

Here in the question, O₂N--CH₂---CH₂O⁻  is more stable carboanion than  CH₃---CHO⁻  because the presentation of --NO₂ group, and --NO₂ is electron withdrawing group due to this it has -I effect, this leads to the dispersal of negative charge. on the other hand -CH₃ group has +I effect{-CH₃ is electron releasing group } . this leads to the intensification of negative charge.
   As you know, in carboanions, dispersal of negative charge is more stable than intensification of negative charge.
that's why O₂N--CH₂---CH₂O⁻ is more stable .
   

Answer 2

Answer:

NO2 group is an electron-withdrawing group. Hence, it shows –I effect. By withdrawing the electrons toward it, the NO2 group decreases the negative charge on the compound, thereby stabilising it. On the other hand, ethyl group is an electron-releasing group. Hence, the ethyl group shows +I effect. This increases the negative charge on the compound, thereby destabilising it. Hence, O2NCH2CH2O– is expected to be more stable than CH3CH2O–.