What is structure of lactose? [closed]

Please look at stereochemistry of anomeric carbon or carbon no. 1 of glucose unit. Which among two is correct structure of lactose?

If, both are correct, then how?

Note : Image 1 is from Harper biochemistry

• – Anubhav Goel Aug 13 '17 at 22:40

1 Answer

Both of the images are lactose. The first image is $\alpha$-lactose and the second is $\beta$-lactose. The difference between $\alpha$ and $\beta$ lactose is the orientation of the most right hydroxy (OH) group in the pictures.

• Sorry, can you please focus on OH group at carbon 1.. – Anubhav Goel Aug 13 '17 at 22:06
• When you say carbon 1, I assume you are refering to the carbon next the red "1". There is no OH group at this particular carbon. The four bonds to this carbons is -O-, -O-, -C- and -H – Erik Kjellgren Aug 13 '17 at 22:08
• Sorry again, anomeric carbon please. – Anubhav Goel Aug 13 '17 at 22:11
• @AnubhavGoel I edited my answer to include this difference – Erik Kjellgren Aug 13 '17 at 22:17
• But both show beta glycosidic bonds? – Anubhav Goel Aug 13 '17 at 22:20