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Heat of hydrogenation of benzene is 51 kcal/mol and 
its resonance energy is 36 kcal/mol. Then the heats 
of hydrogenation of cyclohexadiene and cyclohexene 
per mole respectively are
  • a)
    58 kcal, 58 kcal
  • b)
    25 kcal, 29 kcal
  • c)
    29 kcal, 58 kcal
  • d)
    58 kcal, 29 kcal
Correct answer is option 'D'. Can you explain this answer?
Verified Answer
Heat of hydrogenation of benzene is 51 kcal/mol andits resonance energ...
Total energy to break 3 bond in benzene is 87 [51+36].
So to break one bond i.e. in cyclohexaene is 87/3= 29kcal/mol.
And to break 2 bond i.e.in cyclohexadiene is 29*2= 58 kcal/mole.
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Most Upvoted Answer
Heat of hydrogenation of benzene is 51 kcal/mol andits resonance energ...
Heat of Hydrogenation and Resonance Energy

- Heat of hydrogenation is the amount of heat released when one mole of a compound is saturated with hydrogen. It is a measure of the stability of the compound.
- Resonance energy is the difference in energy between the actual molecule and the most stable contributing resonance structure. It is a measure of the delocalization of electrons in the molecule.

Heat of Hydrogenation of Benzene

- Benzene has a resonance structure in which the pi electrons are delocalized over the entire ring, making it more stable than a hypothetical cyclohexatriene with localized double bonds.
- The heat of hydrogenation of benzene is less than the heat of hydrogenation of cyclohexatriene because less energy is released when the pi electrons are localized in the latter.

Heat of Hydrogenation of Cyclohexadiene

- Cyclohexadiene has two double bonds, which can be in either a cis or trans configuration.
- The heat of hydrogenation of cis-cyclohexadiene is more than the heat of hydrogenation of trans-cyclohexadiene because the cis isomer has more steric strain.

Heat of Hydrogenation of Cyclohexene

- Cyclohexene has one double bond, which is localized.
- The heat of hydrogenation of cyclohexene is less than the heat of hydrogenation of cis-cyclohexadiene because the pi electrons in cyclohexene are delocalized over the entire ring, making it more stable than the cis isomer.

Solution

- The resonance energy of benzene is 36 kcal/mol.
- The heat of hydrogenation of benzene is 51 kcal/mol.
- The difference between the heat of hydrogenation of benzene and the heat of hydrogenation of cyclohexene is the resonance energy of benzene, which is 36 kcal/mol.
- Therefore, the heat of hydrogenation of cyclohexene is 51 - 36 = 15 kcal/mol.
- The heat of hydrogenation of cyclohexadiene can be calculated as follows:

- The heat of hydrogenation of cis-cyclohexadiene is 49 kcal/mol (approximately the same as that of cyclohexene).
- The heat of hydrogenation of trans-cyclohexadiene is 34 kcal/mol (approximately the same as that of cyclohexene).
- The average of these two values is (49 + 34)/2 = 41.5 kcal/mol.

- Therefore, the heat of hydrogenation of cyclohexadiene is 41.5 kcal/mol.
- The correct answer is option D, which gives the heat of hydrogenation of cyclohexene as 15 kcal/mol and the heat of hydrogenation of cyclohexadiene as 41.5 kcal/mol.
Community Answer
Heat of hydrogenation of benzene is 51 kcal/mol andits resonance energ...
See first total energy to break 3 bond in benzene is 87 [51+36]
.so to break one bond i.e. in cyclohexaene is 87/3=29kcal/mol.
and to break 2 bond i.e.in cyclohexadiene is 58 kcal/mole.
if you find diffulcity ask me i solve it on paper .
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Heat of hydrogenation of benzene is 51 kcal/mol andits resonance energy is 36 kcal/mol. Then the heatsof hydrogenation of cyclohexadiene and cyclohexeneper mole respectively area)58 kcal, 58 kcalb)25 kcal, 29 kcalc)29 kcal, 58 kcald)58 kcal, 29 kcalCorrect answer is option 'D'. Can you explain this answer?
Question Description
Heat of hydrogenation of benzene is 51 kcal/mol andits resonance energy is 36 kcal/mol. Then the heatsof hydrogenation of cyclohexadiene and cyclohexeneper mole respectively area)58 kcal, 58 kcalb)25 kcal, 29 kcalc)29 kcal, 58 kcald)58 kcal, 29 kcalCorrect answer is option 'D'. Can you explain this answer? for NEET 2024 is part of NEET preparation. The Question and answers have been prepared according to the NEET exam syllabus. Information about Heat of hydrogenation of benzene is 51 kcal/mol andits resonance energy is 36 kcal/mol. Then the heatsof hydrogenation of cyclohexadiene and cyclohexeneper mole respectively area)58 kcal, 58 kcalb)25 kcal, 29 kcalc)29 kcal, 58 kcald)58 kcal, 29 kcalCorrect answer is option 'D'. Can you explain this answer? covers all topics & solutions for NEET 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for Heat of hydrogenation of benzene is 51 kcal/mol andits resonance energy is 36 kcal/mol. Then the heatsof hydrogenation of cyclohexadiene and cyclohexeneper mole respectively area)58 kcal, 58 kcalb)25 kcal, 29 kcalc)29 kcal, 58 kcald)58 kcal, 29 kcalCorrect answer is option 'D'. Can you explain this answer?.
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