Structures of compounds

what should be the ideal explanation behind the order of stability of these three compounds?


In these three examples the first two structures have a positive mesomeric effect and it is greater in case of fluorine due to 2p-2p orbital overlap where as in case of chlorine it is a 3p-2p orbital overlap and in the third case there is no such effect. overlapping factor has more importance while considered in acidic strength.

and order of stability should be: i>ii>iii


The Inductive effect has a higher precedence over mesomeric effect in case of halogens present and since F is more electronegative than Cl the least stable structure will be the first one and then the second least stable is the second structure

and order of stability should be: iii>ii>i

which explanation is correct and where am I going wrong?

  • $\begingroup$ Mesomeric effect can only be applied for a conjugated system sind this alkyl halide and alkane are not showing such configuration we'll go with inductive effect $\endgroup$
    – user145624
    Commented Apr 27 at 15:28
  • $\begingroup$ @user145624 Maybe I have misleading phrases in my post. But you are saying a lone pair adjacent to a carbocation cannot stabilize it? $\endgroup$ Commented Apr 27 at 15:55
  • $\begingroup$ It may be called hyperconjugation as by hydrogen in structure II. Halogen have ability to do the same as in the case of bromination of alkene (e.g., bromonium ion intermediate). $\endgroup$ Commented Apr 27 at 22:44


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