Question

What are the observations against an open-chain structure for the glucose molecule?

Answer 1

Open-chain structure for the glucose

• When glucose is heated with methyl alcohol in the presence of dry HCl gas, it produces two isomeric methyl glucosides.

${\mathrm{C}}_6{\mathrm{H}}_{12}{\mathrm{O}}_6+{\mathrm{CH}}_3\mathrm{OH}\to \mathrm{\alpha }-{\mathrm{C}}_6{\mathrm{H}}_{11}{\mathrm{O}}_6{\mathrm{CH}}_3+\mathrm{\beta }-{\mathrm{C}}_6{\mathrm{H}}_{11}{\mathrm{O}}_6{\mathrm{CH}}_3$

• The open chain structure of glucose does not predict this test.
• Despite having an aldehydic group, glucose does not give the 2,4-DNP test, Schiff's test, or hydrogen sulphite addition product.
• The ring structure of glucose explains this phenomenon.