Question

Five-membered ring structures of fructose are given below. Mark the incorrect statement.

A) The five-membered ring structures are named furanose structures
B) The cyclic structures represent two anomers of fructose
C) Five-membered ring structures are named pyranose structures
D) These are also called Haworth structures

Answer 1

Hint:The furanose ring has an oxygen atom in it. Anomers are the structures which are cyclic monosaccharides that are epimers of each other. Analyze the given options carefully and relate the terms with the given structures and select out the incorrect statement.

Complete step by step answer:
1) First of all we will observe the given structures and relate them with the given options one by one. The structure given is fructose which has a different arrangement at carbon number one.
2) Option A states that both the structures are named as furanose which is a correct statement as both the rings of the structure contain oxygen atoms in it which is named as furanose. Hence, this option is correct.
3) Now the option B states that the cyclic structures represent two anomers of fructose. The anomers are the structures which are the monosaccharide cyclic structures which differ from each other at the C-1 in the structure. In this case, the arrangement of molecules is different at C-1 which shows this option is correct.
4) In option C states that the structure is pyranose. In the structure of pyranose, there are six-membered rings which have five carbon in it and this doesn’t match with the given structures. Hence, this option is incorrect.
5) The option D states that these structures are Haworth structures which is correct as they show three dimensional perspectives. Hence this statement is correct.
Therefore, the statement in option C is incorrect and the correct choice of answer.

Note: Furanose structure is a five-membered ring having four carbon atoms and one oxygen atom in it. In the case of pyranose, it is a six-membered ring having four carbon atoms and one oxygen atom. The carbon atoms where the epimers are present are called anomeric carbon or anomeric center which in the case of fructose is C-1.