Organic help

  • Thread starter ddrplayboy
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  • #1
can any body help me to answer this question?
Comoplete hydrogenation of 1,3,5,7-cyclooctatetraene is exothermic by -101 kcal/mole. Hydrogenation of cyclooctene proceeds with delta H equal to -23kcal/mol. On the basis of these data, would you call cyclooctatetraene armotic? Justify your anser. Would you expect more than one distinct isomer of 1,2-dimethylcyclooctatetrane to exist? If so, explain our reasoning.
 

Answers and Replies

  • #2
chem_tr
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Hello, four C=C bonds give 101 kcal/mol when saturated, so one bond would give one fourth of it, equal to 25.25 kcal/mol. The small difference indicates that a tendency to aromatic may be present, but not enough.

About your second question, I'd say that since cyclooctatetraene is a cyclic compound, it is not likely that trans-dimethyl product would be so stable, so only cis-isomer is expected to occur with a considerable magnitude. This is my reasoning, I did not look up anywhere, so I cannot guarantee my last answer.
 
  • #3
GCT
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"Cyclooctatetraene fails both requirements, although it has a ring of sp2 hybridized atoms. This molecule is not planar ( a geometry that would have 135º bond angles ). Angle strain is relieved by adopting a tub-shaped conformation; consequently, the p-orbitals can only overlap as isolated pairs, not over the entire ring. Furthermore, cyclooctatetraene has 8 π-electrons, a number not consistent with the Hückel Rule"

http://www.cem.msu.edu/~reusch/VirtualText/react3.htm
 
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