Both 1,2−dihydronaphthalene and 1,4−dihydronaphthalene may be selectively hydrogenated to 1,2,3,4−tetrahydronaphthalene. One of
these isomers has a heat of hydrogenation of 101 kJ/mol (24.1 kcal/mol), and the heat of hydrogenation of the other is 113 kJ/mol (27.1 kcal/mol). Match the heat of hydrogenation with the appropriate dihydronaphthalene.
1 answer:
Answer:
1,4-dihydro = 113 kJ·mol⁻¹
1,2-dihydro = 101 kJ·mol⁻¹
Explanation:
In 1,4-dihydronaphthalene, the 2,3-double bond is isolated from the benzene ring.
In 1,2-dihydronaphthalene, the 3,4-double bond is conjugated with the benzene ring.
Thus, 1,2-dihydronaphthalene is partially stabilized by resonance interactions between the ring and the double bond (think, styrene).
1,2-Dihydronaphthalene is at a lower energy level because of this stabilization.
The heat of hydrogenation of 1,2-dihydronaphthalene is therefore less than that of the 1,4-isomer when each is hydrogenated to the common product, 1,2,3,4-tetrahydronaphthalene.
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Answer:
Reduced species and oxidizing agent: sulfur in the form of sulfate.
Oxidized species and reducing agent: chromium in the form of chromous hydroxide.
Explanation:
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In this case, for the reaction:
We can see that the oxidation states of sulfur and chromium change from +6 to +4 and +3 to +6 respectively; in such a way, since the oxidized species is the same reducing agent because it undergoes an increase in the oxidation state, we infer that chromium is it as it goes from +3 to +6.
Moreover, since the reduced species is the same oxidizing agent because it undergoes a decrease in the oxidation state, we infer that sulfur is it as it goes from +6 to +4.
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