The bonds attaching the sugar ring to the -CH2OH and to the purine are freely rotating
When both are beta, the 5’-OH can be in ideal distance to H-bond with either N3 of purine or O1 of sugar
The latter already accounted for in YCCY
H-bond with N3 strong even though it forms ring of 8 large atoms.
Needs correction of +0.86 for 84 analogs