[BMS1011] Mutarotation and Haworth Projections

[alondouek]

I'm having trouble understanding mutarotation and how to draw Haworth projections.

Could someone help me out?

[alondouek]

Bump because I'm kinda struggling

[thushan]

Mutarotation is basically where the alpha and beta forms of the cyclic monosaccharide are in equilibrium via the aldehyde form.

alpha-form <--> aldehyde <--> beta form

Haworth projections are the way VCAA used to draw monosaccharides; it is a visual form of the molecule where you are viewing it from the front.

[alondouek]

Mutarotation is basically where the alpha and beta forms of the cyclic monosaccharide are in equilibrium via the aldehyde form.

alpha-form <--> aldehyde <--> beta form

Thanks! Although, I'm unclear as to how this equilibrium develops. If I were to have one molecule of D-glucopyranose in solution, would it alternate continuously between these forms?

If so, why? The alpha- and beta-forms, as well as the linear aldehyde form, don't appear to be unstable... does it have something to do with the alkanol groups? If that is correct, can the degree of mutarotation of that molecule be altered if I manipulate the conditions/properties of the solution?

Sorry for all the questions, this is all very different to VCE chemistry and it's blowing my mind 

[thushan]

Thanks! Although, I'm unclear as to how this equilibrium develops. If I were to have one molecule of D-glucopyranose in solution, would it alternate continuously between these forms?

If so, why? The alpha- and beta-forms, as well as the linear aldehyde form, don't appear to be unstable... does it have something to do with the alkanol groups? If that is correct, can the degree of mutarotation of that molecule be altered if I manipulate the conditions/properties of the solution?

Sorry for all the questions, this is all very different to VCE chemistry and it's blowing my mind 

None of them are unstable; it's an equilibrium system. Analogy: consider 2 SO2 + O2 <--> 2 SO3. This reaction is reversible, but we don't consider SO2, O2 and SO3 as unstable molecules.

alpha-form <--> aldehyde <--> beta form

All these three structures are similarly thermodynamically favourable (which is why the reaction is reversible).

[alondouek]

All these three structures are similarly thermodynamically favourable (which is why the reaction is reversible).

What exactly do you mean by this? I'd inferred that mutarotation of a molecule occurs spontaneously in solution; so does the fact that the varying forms are "thermodynamically favourable" mean that the process is driving itself with regards to energy?

If that's true, I guess it makes sense given that there's both the exothermic breaking of bonds and the endothermic reforming of bonds occurring.

Alternatively, I could still be looking at this all wrong haha