Q&A: Need Orgo Help… “Alkenes Reactions”?

Question by asdig23: Need Orgo help… “alkenes reactions”?
I need help with h/w… which does not have answer on the back of the textbook…

If……

…. 1-methylcyclopentanol under goes “sulfuric acid, 80C” what is the major product (Use the E/Z notation when necessary)

…. 3-chloro-3-methylpentane under goes “sodium ethoxide, ethanol, 70°C” what is the major product (Use the E/Z notation when necessary)

If…

…. 1-iodo-3,3-dimethylpentane under goes “potassium tert-butoxide, tert-butyl alcohol, 100°C” how many alkenes forms?

…. 1-iodo-2,4,6-trimethylcyclohex… under goes “sodium ethoxide, ethanol, 70°C” how many alkenes forms?

Best answer:

Answer by Peter B
… protonation of alcohol, H20 leaves giving 3° carbocation. elimination of beta-H gives: 1-methylcyclopentene (E1)
… symmetrical alkyl halide, then basic elimination of (equivalent) beta-H leads to E-3-methyl-2-pentene (E2)
… huge bulky strong base, great leaving group, only one beta-H that might be removed gives 3,3-dimethyl-1-pentene; only product(E2, Hoffman product)
… symmetrical alkyl halide, makes both available beta-H’s equivalent leading to one elimination product: 1,3,5-trimethylcyclohexene; only product (E2)

Note in above reactions, the use of heat encourages Elimination and minimizes substitution products.

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