Doubt in general organic chemistry

general-organic-chemistry
find-delocalisation
aromaticity
unsolved
easy
pp
#1

#2

In 1,4 delocalisation due to conjugation between all pairs i.e resonance. In 2, 3 conjugation not present between all pairs.

#3

Answer given is 2

#4

Ok, I think in 4 pentavalent nitrogen will be formed if resonance takes place so it's not possible, could be similar for 1 also. Don't know about 3rd

#5

In compound 1 and 4 the delocalisation of positive charge is happening because of resonance.

In 2 and 3 positive charge and pie bond are not in conjugate they are parpendicular. So there is no resonance.

#6

In 1st and 4th option delocalisation is not possible as oxygen cannot make more than 3 bonds and nitrogen cannot make more than 4 bonds.In 3rd option +ve charge is on bridge head carbon..so it cannot be delocalised.
In 2nd option if we break double bond between carbon and nitrogen then delocalisation is possible.

#7

Yes you are correct.i didn’t get the number bond of oxygen and nitrogen are forming after resonance.