Question

Question 1: Compare the possible ring structures and conformers for fructose and decide which is preferred (if any). There are four main hemi-ketal rings, one of which is shown below. What factors might influence the preference for 5- or 6-membered rings?

Question 2: Make a model of vitamin C. Note the lactone link that forms the ring, rather than the hemi-ketal that is present in fructose. Do you think the presence of sp² carbons in the ring induce strain? Does this influence the conformer shape? How many possible stereoisomers are theoretically possible for this molecule? Explain your answer.

Question 3: Draw a Fischer Projection of D-Fructose. Use Fischer Projections to represent all possible stereo-isomers of D-Fructose. Would any of these form more stable hemi-ketal ring structures than D-fructofurnaose?

Question 4: Compare the possible conformers for the following molecule and decide which is preferred (if any).

Question 5: What happens to the shape of the molecule shown below when it undergoes a conformational change form chair to chair? Explain your answer.

CH-Oн ОН Но CH-ОН OH B-D-Fructofuranose OH HO H =O Na OH

Answer 1

1 Fischers pection of D-fructose Passible steaeoisomers of -futose CH20H where, CH20H 1 iral of Ho-c-H Cetres = 2 22 2-g H-C-0H HO-C as h aun hel CH0H HO-C CH2CH D-fuctose (IT. Enan tiomers CH20H CH20H CH20H CH 20H =0 H-C-CH HOC HO H H H CH2OH CH20H CH2OH (T) Enowt oncy Ene ntcnmers HDLH H- Ho--H CH2OH Hon Enantrme he: 4 Conforncer the felaAing Profearedcenyfaus matum arbotkbutg) T930 P Ge ee-p CSchon D ga alions. (T Other cenfus meas f e,e-isoer CIZ (TU) Trans 1.S-di-4 -buty! decali Ca,a-isomev ciss-di-butyl de cod

Gues Conformational changes Char to chai 1 more ste le Less Stable (I) Trans- 2,6-Dimethyl de caim Tacns-26-Dimethy ecain caa isomer (e,e-isomer) Two axicl mehyl qauups NO gauch butane nte ra ctrems to t gauche butane bence due to equatorial methyl gouups tera ctios' (2+2)4 colfn ole eneasy 3-6 k Hemce 55e1