how do u form mannose w/ glucose through dehydration synthesis. I don't know what a glucose molecule looks like.

if you don`t mind me asking Why do you want to make Mannose? is it as a precursor for Mannitol by any chance?

Mannose is one of the three main hexoses in most organisms and plays a critical role in the glycosylation of many proteins. Mannose is the oxidized form of the sugar alcohol, mannitol, and mannitol can be formed by the reduction of mannose (e.g. with sodium borohydride).

 

In most organisms, glucose is converted to mannose via fructose-6-phosphate, an intermediate in glycolysis. The enzyme phosphomannose isomerase catalyzes this conversion. The enzyme likely catalyzes the formation of an enol which can be tautomerized in a stereospecific manner to generate mannose-6-phosphate. The mannose-6-phosphate is then converted to mannose-1-phosphate using phosphomannomutase. Unphosphorylated mannose is not synthesized in vivo because the phosphorylated (and guanosylated) forms are the most biosynthetically useful.

 

As for how dehydration synthesis fits in, I'm not sure as I don't believe any of the steps involve condensation reactions. Perhaps the chemical synthesis of mannose involes a dehydration step to produce an achiral double bond, which can then be stereospecifically hydrated for form mannose.