Ochem -- Berkeley Review Full Length Error or what?

[MCAT guy]

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[MCAT guy]

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[orgohacks]

They even say in the solution that they are both tetra substituted but then upon hydrolysis, how does the OCH3 come off????

They are both tetrasubstituted, but if you look at the 4-position of the galactose (the one on the right) it is not attached to a methyl group, but to the mannose.

This is acidic hydrolysis. The anomeric positions go from acetals to hemiacetals. Since the glycosidic linkage is 1,4 , hydrolysis means that the 4-position of the galactose will go from O-mannose to OH.

 

[MCAT guy]

They are both tetrasubstituted, but if you look at the 4-position of the galactose (the one on the right) it is not attached to a methyl group, but to the mannose.

This is acidic hydrolysis. The anomeric positions go from acetals to hemiacetals. Since the glycosidic linkage is 1,4 , hydrolysis means that the 4-position of the galactose will go from O-mannose to OH.

Yeah but the anomeric carbon for galactose (carbon 1 which was methylated) is not methylated in the final product. I see the acetal change, I'm talking about the one NOT involved in th glycosidic linkage, it still has disappeared on galactose carbon 1

 

[orgohacks]

Yeah but the anomeric carbon for galactose (carbon 1 which was methylated) is not methylated in the final product. I see the acetal change, I'm talking about the one NOT involved in th glycosidic linkage, it still has disappeared on galactose carbon 1

Acidic hydrolysis will replace *all* anomeric OR groups with OH, whether they are involved in glycosidic linkages or not.
hope this helps - James

 

[MCAT guy]

Acidic hydrolysis will replace *all* anomeric OR groups with OH, whether they are involved in glycosidic linkages or not.
hope this helps - James

thanks dude, totally didn't remember that all anomeric OR groups change. Not sure if I ever learned that or what.