3
$\begingroup$

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 .

Improve this question
$\endgroup$

1 Answer 1

Reset to default
4
$\begingroup$

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

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

Similarly Beta D-fructo furanose gives an intermediate 3 and 4 by protonation at anomeric carbon. enter image description here

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

enter image description here

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

The above diagrams are author drawn in CHEM DRAW

Improve this answer
$\endgroup$
4
  • 1
    $\begingroup$ This entire answer appears to be copy-pasted from Bruice's Organic chemistry. If you are quoting third-party sources, or using any graphics/data/plots that are not made by you, put an appropriate reference and denote the part that is quoted with proper markup (>). Keep in mind that if you don't that you may eventually be accused of plagiarism. $\endgroup$
    – andselisk ♦
    Commented May 26, 2019 at 7:23
  • $\begingroup$ @user226375 your question is answered now, $\endgroup$
    – Chakravarthy Kalyan
    Commented May 26, 2019 at 8:42
  • $\begingroup$ @andselisk you were correect .This was taken from Bruice's Organic chemistry.(missed reference ).How ever the answer is rewritten ti the question asked .The diagrams are mine , drawn on CHEMDRAW. $\endgroup$
    – Chakravarthy Kalyan
    Commented May 26, 2019 at 8:44
  • 2
    $\begingroup$ @andselisk I MISSED QUOTING REFERENECE IN HURRY TO ANSWER .MY APOLOGIES .THIS WAS NOT DONE ON PURPOUSE. $\endgroup$
    – Chakravarthy Kalyan
    Commented May 26, 2019 at 8:52

Not the answer you're looking for? Browse other questions tagged or ask your own question.