Fructose contains a keto group, yet it reduces Fehling solution and Tollen's reagent. Why ?

Fructose although contains a ketone group yet it acts as a reducing sugar. This is explained by the formation of glucose from fructose by enolisation. Enolisation results in the formation of glucose from fructose and vice versa. (Lobry de Bruyn Van Ekenstein rearrangement).

There are two -NH2 groups in semicarbazide that might react with a ketone or aldehyde. Explain why the reaction occurs with only one -NH2.

The -NH₂ group closer to the carbonyl group is deactivated (resonance-stabilized) compared with the other end -NH₂ group:

Related Questions:

Penta-1,3-diene is more stable than penta-1,4 -diene. Why?

Phenoxide ion is more stable than an alkaoxide. why?

Why does aqueous sodium bicarbonate solution dissolve carboxylic acids but not phenol though they are also acidic ?

Why enol form of Beta Dicarbonyl compound more stable than those of monocarbonyl compounds?

Why enol form of phenol is more stable than its keto isomers?

Reactivity order of Pyrrole, Furan and Thiophene towards Electrophilic substitution :

Phenyl group is known to extract negative inductive effect, but each phenyl ring in biphenyl is more reactive than benzene towards Electrophilic substation. Why?

Chloroform is more acidic than fluoroform why?

Fluorine is more electronegative than chlorine even then, p-flurobenzoic acid is weaker acid than p-chlorobenzoic acid explain ? 

Trifluoroethyl carbocation is less stable than trifluromethyl carbocation why ?

Why is the Tropylium carbocation less stable than the tricyclopropylmethyl carbocation?

How does it account for benzene's extraordinary stability ? Give an orbiial picture of benzene ?

The ring is comprised of six sp2 hybridized carbon's each sigma bonded  to carbon’s and an H. (Fig-1) Each Carbon  also has a "p" AO with one electron :  the AO's project above and below the plane of the ring which is a nodal plane. Rather than form three localized alternating doubic bonds (cycIohexatriene). these "p" AO's overlap  laterally to form an extended π-system in which the electrons  are symmetrically delocalized over all six carbon's making the Carbon's equivalent . (Fig-2) Delocalization results in less electron repulsion, greater stabilizalion, and lower energy.

Related Questions: 
Is Benzene same as 1,3,5-Cyclohexatriene ?
Which halogen best delocalises electron density to benzene ring?
Nitrobenzene and not benzene, is used as a solvent for Friedel Craft alkylation of bromobenzene. Why ?
Why tetraalkylammonium ion ((CH3)4 N+) is neither an electrophile nor a nucleophile and H3O+ is not nucleophile but electrophile although it contains a lone pair of electrons.
Why does not carbon form C+4 or C-4 ions? Explain.
Which halogen best delocalises electron density to benzene ring ?
What is Lindlar’s catalyst and does Lindlar’s catalyst use ?
Fluorine is more electronegative than chlorine even then, p-flurobenzoic acid is weaker acid than p-chlorobenzoic acid explain ?