Glucose exists in humans predominantly as a-D-(d) glucopyranose

NEET SS
#1

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

    1. a
    1. b
    1. ce
    1. ae
    1. 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 :-
  1. 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 (-)