How are glycosidic linkages formed?

Consider glycosidic linkages in disaccharides.


I know a condensation reaction occurs, with the loss of water.


But which OH is lost? The O in the linkage belongs to which monosaccharide?


Example: take sucrose, the O in the linkage belongs to fructose or glucose?


I couldn't find any literature regarding this. Any help is appreciated .




In sucrose molecule the glycosidic linkage is formed by the OH group on the anomeric carbon of α-D-glucose and the OH group on the anomeric carbon of β-D-fructose.


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


source : 


<https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Map%3A_Organic_Chemistry_(McMurry)/Chapter_25%3A_Biomolecules%3A_Carbohydrates/25.08_Disaccharides>


As seen, in either alpha d-glucose or beta d-fructo furanose may react to give sucrose.


Let us examin.


Alpha D-gluco Pyranose gives an intermediate **1** and **2** by protonation at anomeric carbon. 


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


Similarly Beta D-fructo furanose gives an intermediate **3** and **4** by protonation at anomeric carbon.
[![enter image description here](https://i.stack.imgur.com/DJkfD.png)](https://i.stack.imgur.com/DJkfD.png)


If you examine , structure 3 is more stable then structure 4.


[![enter image description here](https://i.stack.imgur.com/z0Psx.png)](https://i.stack.imgur.com/z0Psx.png)


The negative inductive effect of CH2OH in fructofuranose destablizes this intermediate 4.


Hence structure 2 , an intermediate of aplha D-gluco pyranose (**more stable**) attacks beta D-fructo furanose togive sucrose.


[![enter image description here](https://i.stack.imgur.com/xvFO3.png)](https://i.stack.imgur.com/xvFO3.png) 




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The above diagrams are author drawn in CHEM DRAW


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