the double helix is hydrogen bonded through the bases only so the bases are inside the helix only
as adenine combines with thymine and guanine with cytosine
phosphate are in the exterior of it
sugar groups constitute the double helix.
The reason does FeCl3 serve in the electrophilic sweet-smelling substitution response amongst chlorine and benzene is that it fills in as a Lewis corrosive impetus by responding with the Cl2 and along these lines actuates it toward assault by benzene's π electrons.
