How do you explain the presence of all the six carbon atoms in glucose in a straight chain?

Explanation

Glucose on heating with HI produces n-hexane,
`overset(" "CHO)overset(|)underset(" ""Glucose")underset(" "CH_(2)OH)underset(|)(" "(CHOH)_(4))overset(HI)underset(Delta)rarr CH_(3)-CH_(2)-underset("n-hexane")(CH_(2)-CH_(2))-CH_(2)-CH_(3)`
This suggests that all the six carbon atoms of glucose are linked in a striaght chain.