Formation of sucrose from glucose and fructose

[Stevie D]

This is my first post here, so hello everyone. Making my foray into the wonderful world of science via an Access course (read A-level for mature students) in Marine and Environmental Science. See you at the lab in a few years' time.

 

Anyway, onto the question. Working away on a biochemistry module at the moment (RH5/3/WW/003). Trying to rationalise to myself the formation of sucrose from glucose and fructose, as you may have determined from the thread title.

 

I found this website: http://dl.clackamas.edu/ch106-07/sucrose.htm

 

What I don't understand is their explantion of how b-D-fructose in standard orientation, shown here:

 

 

...gets flipped to b-D-fructose in inverted orientation:

 

 

Are these two separate isomers? I've tried mentally rotating the first molecule in all three dimensions but still can't find a way to do it so that it ends up looking like the second one. I'd appreciate an explanation by more learned people.

 

Cheers,

 

Steve

[science101]

I can ashore you steve that it is not possible. Sorry about your problem, no help here.

[zule]

In order to go from an isomer to the other, the ring has to open ant then to close again in the new conformation. This is called mutarotation.

[Abdulkareem]

the problem u have there is the ring is not easy simplify and u u can find other ring i can explain it for in a simple manner. u know sucrose hydrolysis by formation of glucose and fructose.

[Stevie D]

In order to go from an isomer to the other, the ring has to open ant then to close again in the new conformation. This is called mutarotation.

I see, thanks.

[MBGuru]

Draw a line that goes through the furan ring Oxygen atom and splits in half the bond that connects Carbon atoms 3 and 4, that would be the ones closest to you and each one of them is conected to a -OH group.

 

C4-----C3

 

Now spin the top molecule by 180 degrees and you will get the one on the bottom. But this time C4 will be to your right and C3 to your left.