Organic 2 Review Problem 151

Organic 2 Review Problem 151 - (although they are not of...

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PREPARATIONS 135 particularly those of reduction and of osazone formation, are due to these groups. H OH HO H V \/ I C • — I 2 HCOH I 3 HOCH \^ I HCOH I HOCH i 2 3 L,J1U I HCOH I HOCH IMU L,W,U11 I UM 1 Ul-I \/ I -i /"* 2 L> I 3 HOCH 2 CO I 3 HOCH I o I o I I o I 4 HCOH I HCOH I I 5 HC 1 HC 1 I 6 CH,OH CH 1 OH 4 5 6 a-Glucose p-Glucose (I)* (II)* HCOH I HCOH I CH 8 OH Glucose (III) 4 HCOH I 5 HCOH I 6 CH, 1 4 HCOH I 5 HCOH I 6 CH 1 OH P-Fmctose Fructose (IV)* (V) It will be seen that the ring form of glucose can exist in two isomeric forms <x and (3, which differ only with regard to the disposition of the H and the OH groups around carbon atom i, since if the ring is regarded (for simplicity) as being in the plane of the paper, a-glucose (I) may have this H atom above, and the OH group below, the plane of the paper, whilst ^-glucose (II) will have the H atom below, and the OH group above this plane. These ring structures for a and {3-glucose can alternatively be represented by (VI) and (VII). a and OH OH (VI)* (VII)* p-glucose, when dissolved in water, have different optical rotatory powers
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Unformatted text preview: (although they are not of course optical enantiomorphs, as the above formulae show): the optical rotation of each solution changes slowly on stand-ing, and the final value attained is identical in each case, i.e. . a mixture of both forms in equilibrium is ultimately obtained from either a or p-glucose. The difference between a- and (3-glucose disappears in the straight chain form (III), and since it is in this form that glucose often appears to react, this difference between the a and P forms can often be ignored in practical work. Fructose exists similarly in two forms, determined by the disposition of the OH and * Structures (I), (II) and (IV) are convenient projection formulae; formulae such as (IV) and (VII) are more realistic representations, but even these are only approximations as the rings are not flat....
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This note was uploaded on 09/19/2011 for the course CHM 2211 taught by Professor Castalleano during the Fall '06 term at University of Florida.

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