Chemistry NCERT Exemplar Solutions Class 11th Chapter Twelve

18. In this structure  i.e.,   3-nitrocyclohex-l-en (Carbon atoms of the ring are numbered in such a way that double bonded carbon gets the lowest number followed by the nitro group -NO₂.    

24. In this structure i.e., 3-ethyl, 4-methylhept-5-en-2-one. (the longest carbon  chain is selected in such a way that the functional group > C = O gets the lowest possible locant.

22. Four possible carbocations can be obtained from 2- methyl butane  are 

Generally, order of stability follows the order-

1° carbocation < 2 carbocation < 3 carbocation 

Order of increasing stability of the given structures is-

I < IV < II < III.

21. Triphenylmethyl cation is found to be very much stable as this positive charge on methyl carbon is delocalized in three phenyl rings. In each phenyl ring, positive charge is developed on 2 ortho position and para position, i.e., three resonating structures. Total resonating structures given by triphenylmethyl cation are nine. Hence, it is very stable. These structures can be shown as.

20. The structure A is more stable than structure B. This is because carbocation A is more Planar and? electrons from the ring shift to the side group and are stabilized by resonance while structure B is non-planar and does not undergo resonance. Also, double bond is more stable within the ring as compared to the side chain.

19. The resonating structures can be drawn as-

In structure I, CH₂ group has the positive charge which means octet is not completed, but in structure II, both the carbon atoms and oxygen atom have complete octet hence, more stable.

18. If a liquid compound decomposes at its boiling point but is steam volatile and insoluble in water and stable at low pressure. Then steam distillation method can be used for its purification. 

Note : Answer the questions 35 to 38 on the basis of information given below:

“Stability of carbocations depends upon the electron releasing inductive effect of groups adjacent to positively charged carbon atom involvement of neighbouring groups in hyperconjugation and resonance.”

17. In DNA and RNA, nitrogen is present in heterocyclic base and also present in the ring but not as a substituent. Therefore, nitrogen present in the ring cannot be converted into (NH₄ )2SO₄. Hence, it cannot be estimated by Kjeldahl method. 

16. In accordance with the IUPAC nomenclature, the longest carbon chain is selected such that it must have maximum functional groups present in the compound. Therefore, only in one selected chain of 4 carbon atoms including both the functional group is corrected one. 

While in the other three, carbon atoms are in the selected chain, but both the functional groups are not included.