Which of the following are enantiomers
a) D-Galactose & L-Glucose
b) d-Galactose & l-Glucose
c) D-Mannose & L-Mannose
d) d-Mannose & l-Mannose
e) D-glucose and L- glucose
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- a
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- b
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- ce
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- ae
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- cd
0 voters
exp:
D-Mannose & L-Mannose & `e’ i.e., D-glucose and L glucose
- Enantiomers are D and L forms of same sugars.
- So, D-glucose and L-glucose are enantiomers of each other. Similarly, D-mannose is enantiomer of L-maimose and D-galactose is enantiomer of L-galactose.
- Option ‘d’ requires some explanation. d-mannose and L-mannose are optical isomers.
- When we use the capital letter, i.e. D or L, it refer to the orientation of H and OH group on penultimate corbon atom, i.e. adjacent to the terminal primary alcohol carbon. If -OH group is on right, it is D-isomer and if-on group is on left it is L-isomer, and both are enantiomers of each other.
- On the other hand, when we use small letters ‘1’ and ‘d’, it refers to optical isomerism. If the polarized light is rotated to the right by a solution of optical isomers, it is called dextrorotatoiy (d) or (+) and if light is rotated to the left, it is called levorotatory (l) or (–).
- So, D-mannose and L-mannose are enantiomers of each other, whereas d-mannose and 1-mannose are optical isomers of each other. Following example will clear all doubts :-
- Glucose exists in humans predominantly as a-D-(d) glucopyranose. This means that the form is a-anomer, D-enantiomer along with rotating to right (dextrotatory) in pyranose form.
- Anomers → α and β
- Enantiomers → -D and -L
- Optical isomers → d- and 1- or (+) and (-)