Actually the mechanism is not like that, that this is just replaced by OH coming from the back side OH means OH from water, okay, because if you look at the configuration, this is S and the product that is also S that means there is retention of configuration, that means this oxygen has not come from the water from the back side, because then it would have been R.
ಅಂದರೆ ಅರ್ಥ, ಆಕ್ಸಿಜನ್  ಹಿಂಬದಿಯಿಂದ ವಾಟರ್ ನಿಂದ ಬಂದಿಲ್ಲ,ಆಗಿದ್ದರೆ, ಇದು  ಆರ್ ಆಗಿರಬೇಕಿತ್ತು.