Question

14. Consider some of the 16 different stereoisomers of the following sugar: CHO ÇHO сно CHO CHO H OH HOHH OHHO+ HH OH H-OH нон HO+H HOTH Антон H OH нон H +OHH OHHO+H H-OH H+OH Антон нон нтон снуон CH OH CHO CHOH CHOH D-allose D-aitrose D-glucose D-mannose D-gulose - 140 +33° +53 +14° -20° CHO HO+ HO+H HO+H HO- H CHOH L-allose CHO CHO сно CHO H+H HOH OH OH HO- H нон нон нонн HO+H Нонн нонн ннон HOH HOHHOHHOH CH2OH CH201 CH2OH CHOH L-altrose L-glucose L-mannose L-gulose -140 200 - 140 -330 -53 What is the relationship between D-allose and L-allose? Compare their optical rotations. What is the relationship between D-allose and D-altrose? Compare their optical rotations, The molecule, D-talose, shown below is another stereoisomer of allose. Comment on its optical rotation. CHO HOH HO+H HO+H НЕОН Сн,он D-talose

Answer 1

Relation bro D-allose and L-allose. HO TH HOTH HOFAH To check CHO Relation - Enantiomersets - CHO H-T — он : .. Но —н по пеr oPrico4 , we Hou QH. но * Н rotation, HOH Н -- Оңкно — на OH Сн, оң CH₂OH &H₂O4 CHROM D-allose L-allose 1140 . -14° use a mirror to find check the the steresisomer we often relation between out if they are mirror images or not. Suppose, we put a mirror between D-allose & L-allose, we can see they that the compounds are mirror images of each other as there is an inversion of compound but when we try to put one above thera other. They don't super pose. . overall conclusion we can make is they are non-superposable mirror images nages. and and such such comp compounds are called Enantiomer and this is also the definition of Enantiomers. Now, let's talk about optial rotation /optical activity. D-allose and L-allose are seperatly optically, active i.e. They rotate monochromatic light at some angle but as we have concluded. above that they are enantiomers Tomers and and and and equimmoder equimoker af sdurion o Cmentiomer is called a macemic mixture, which is optically fnactive, HOW? Let's see, , An equimolar mixture means they are present in same amount. Now, as we know they are seperately optically active but the Onantiomers fact about is First compound rotates the Other light at to them the rotates it of at -A as in D and light at ti4o L-allose. D-allose and talloses at 2140. Therefore, there will be no net (0°) rotates rotation in a racemic mixture. b-all i Thallosa equinolay Solution ay D-allose and 'L-allose. Note :~ The magnitude of optical rotation ignore the sign. but with sign rotarion, of both are same if we they have opposite oprical Scanned with CamScanner

Relation between D-allose and Doeltrose. | CHO ! CHO Melation – diastereomers. H-TOH 1 HotOH : 1 H OH 1 H- OH D-dtrose has higher optical rotation, H — он - OH +140 CHOH cң, он D-allose D-altrose. . : +33° In this compound even if we seperate thew by a mirror, they do not form a mirray images, as a red marked Carbon has -OH on the .R. His.. Therefore, they are not mirror images althourlyn The commectivity of group is still the same. Such relations are Go Called diastereomers. Therefore, the compounds are diastereomers. D-altrose has higher optial rotation than D-allose in the same at direction. Therefore, they are oprically to active and theist solution will also be oprically active. . CHO H047H но—— Н HO- HY H OH ch,он E De Talose D-talose is opti@ally active. To find out jj a molecule is chiral Coprically active) we look for elements of symmetry in it. If any type of element of symmetry is present then the molecule is optically inactive. Similarly in D- talosé There is no element of symmetry like plane of Symmetry ar center of Symmetry. Therefore the compound is optically active and has some Optical rotation. Note that it is also a diastereomer of allose. Scanned with CamScanner

One more thing is that optical rotation is not possible to measured theoretically without knowing its observed rotation. We can only say if a compound is optically active or inactive I.e, it either have optical rotation or it doesn't by looking at the elements of symmetry or we can say centre or plane of symmetry. Optical rotation do not depend on the axis of symmetry. But in case you need it optical rotation of D- talose is around +23⁰.

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