[Nitin_Naudiyal]

D - (-) - Fructose

Here does D represent -  Dextro Rotatory ?
and if it does then why is there a  (-) (minus symbol) in the name, isnt - (minus) a symbol for Leavo Rotatory compounds?

Maltose ( α - anomer ) -
It is said that it is a reducing sugar because a free aldehyde group can be produced at C - 1 in second glucose molecule.

But where is the free aldehyde group ?
and it is said it can be produced , but how ?

I have attached the pics for both the compounds

[sjb]

D - (-) - Fructose

Here does D represent -  Dextro Rotatory ?
and if it does then why is there a  (-) (minus symbol) in the name, isnt - (minus) a symbol for Leavo Rotatory compounds?

Maltose ( α - anomer ) -
It is said that it is a reducing sugar because a free aldehyde group can be produced at C - 1 in second glucose molecule.

But where is the free aldehyde group ?
and it is said it can be produced , but how ?

I have attached the pics for both the compounds

Have a look through http://en.wikipedia.org/w/index.php?title=Monosaccharide&oldid=499492229, for instance

[Dan]

Here does D represent -  Dextro Rotatory ?

No, D/L assignment is made based on a structural relationship to glyceraldehyde, not optical rotation.

Here are several threads on the subject:

http://www.chemicalforums.com/index.php?topic=60366.0
http://www.chemicalforums.com/index.php?topic=60121
http://www.chemicalforums.com/index.php?topic=40641.0

It is said that it is a reducing sugar because a free aldehyde group can be produced at C - 1 in second glucose molecule.

But where is the free aldehyde group ?
and it is said it can be produced , but how ?

The functional group at C1 of glucose (glucopyranose) is a hemiacetal. Loook them up, what do you know about the reactivity/stability of hemiacetals?

[Nitin_Naudiyal]

D - (-) - Fructose

Ok . So here D specifies the configuration of the 'C' atom that is present second from the Bottom and since OH is on the Right it is D - Fructose
and (-) specifies that it is laevo rotatory

The functional group at C1 of glucose (glucopyranose) is a hemiacetal. Loook them up, what do you know about the reactivity/stability of hemiacetals?

Hemiacetal are formed by addition of aldehyde and and Alcohol.
and at C - 1 there is a hemiacetal group present because of which it is a reducing sugar

[Dan]

Ok . So here D specifies the configuration of the 'C' atom that is present second from the Bottom and since OH is on the Right it is D - Fructose
and (-) specifies that it is laevo rotatory

Yes

Hemiacetal are formed by addition of aldehyde and and Alcohol.
and at C - 1 there is a hemiacetal group present because of which it is a reducing sugar

The key is that hemiacetal formation is readily reversible:

Alcohol + aldehyde  hemiacetal

Most sugars exist predominantly in cyclic hemiacetal form, but there is a dynamic equilibrium between linear aldehyde form and cyclic hemiacetal form in solution. As a result, sugars exhibit aldehyde reactivity because there is always a small amount of the linear aldehyde form present in solution.

[Nitin_Naudiyal]

Thank You Dan