Class 11th

27. In this case CH3+ is the most stable species because replacement of H atom by Br atom (-Inductive effect) increases positive charge on the carbon atom and destabilizes the species.

This is a short answer type question as classified in NCERT Exemplar

SO₃ acts as an electrophile as in this, three highly electronegative oxygen atoms are attached to the sulphur atom which makes it electron deficient. It can be shown by resonance that it gets positive charge and acts as an electrophile.

26. (b)CH₃ -CH₂ -CH (Br)-CH₂ -CH₂ -CH₂ -COOH 

26. CH₃ -CH₂ -CH₂ -CH₂ -CH₂ -CH₂ -CH₂Br 

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.