Why does the fructose monomer in sucrose appear different from isolated fructose?

I understood that the representation of fructose is:


[![enter image description here](https://i.stack.imgur.com/75OfO.png)](https://i.stack.imgur.com/75OfO.png)


But during the formation of sucrose:


[![enter image description here](https://i.stack.imgur.com/F4SYE.jpg)](https://i.stack.imgur.com/F4SYE.jpg) 


How did fructose, whose representation is given in the first picture, turn out to be different in the second. I tried to visualize myself rotating the molecule but the position of oxygen changes and it doesn't match with the one in sucrose.




Ah, a (fairly) common conundrum that assails us Chemistry students when we start Biochem. ;-)


At first glance, the fructose molecule in your first picture, and that in the second picture appear to have different conformations:



> 
> [![enter image description here](https://i.stack.imgur.com/sjHO4.png)](https://i.stack.imgur.com/sjHO4.png)
> [![enter image description here](https://i.stack.imgur.com/EzZ57.jpg)](https://i.stack.imgur.com/EzZ57.jpg)
> 
> 
> 


Believe me, they're the same. "How?" you ask? Stay with me here (it requires a little imagination):


Draw a vertical line/axis on your first diagram along the plane of the furanose ring, connecting the oxygen atom at the apex, right down to the middle of the C3-C4 bond. Then rotate the molecule 180 degrees *counter-clockwise*. 


Now compare this with the fructose residue in sucrose.


(*I lack the necessary Org. Chem. sketching tools to depict this... apologies*) 




---


If you weren't able to wrap your head around "rotation" bit, then, let's assign locant numbers to the carbon atoms in the two diagrams and *then* compare them:



> 
> [![enter image description here](https://i.stack.imgur.com/bLTBR.jpg)](https://i.stack.imgur.com/bLTBR.jpg)
> [![enter image description here](https://i.stack.imgur.com/sPY6r.jpg)](https://i.stack.imgur.com/sPY6r.jpg)
> 
> 
>  I've drawn them tiny, my bad 
> 
> 
> 


Must've clicked by now ;)


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