Some Basic Principles and Techniques

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. 

15. These are position isomers as if two or more compounds differ in the position of substituents, functional groups, or multiple bonds but if the molecular formula is same then these are said to be position isomers. Here the functional groups are attached to different carbon atoms in the carbon chain, but the molecular formula is the same. They are not metamers because the number of C atoms on either side of-S- are the same.

14. Carbon is known to be more electronegative than Magnesium and hence Mg acquires partial positive charge while C acquires partial negative charge because the bonded pair of electrons is attracted towards it.

13. Electronegativity of an element is directly proportional to its  s-character. If C is sp3hybridized then s- character is 25%, if it is sp2 hybridized then s-character is 33% and if sp hybridized then s-character is 50%. Hence, sp hybridized carbon has strong hybridization, s electrons are more strongly attracted by nucleus than p-electrons thus electronegativity of carbon increases with increase in s-character.