And so what happens is we have that same type of intramolecular nucleophilic. Additional reaction take place and this attacks this electrophile nucleophilically, forming a purple bond that is shown here. Now, this is an example of the beta Dribribribe. We can also have the alpha D ribofiorness, but only the beta Dribor nose is shown for simplification purposes. Now, unlike six member rings, which exist in the chair confirmation form, five member rings, five member sugar molecules exist in a puckered form we call the envelope form. So why we call it the envelope form?