Questions: Experimental H NMR spectrum: This experiment In the current experimen
ID: 1058214 • Letter: Q
Question
Questions: Experimental H NMR spectrum:This experiment In the current experiment you will dehydrate cis/trans-4-methylcyclohexanol to form 4-methyl- 1-cyclohexene using concentrated phosphoric acid. Sulphuric acid is a much stronger acid that phosphoric acid, but phosphoric acid will still promote the dehydration reaction via carbocation formation, and will avoid the possible side reactions that can occur with sulphuric acid. The product alkene will be removed by simple distillation and analyzed by IR and NMR spectroscopy.
Explanation / Answer
a) Yes. The reaction mixture indeed contains the unreacted methyl cyclohexanol. The cis: trans isomers are in the ratio of 1.93: 1
b) It would be obvious to expect the formation of three alkenes: 1-methyl-1-cyclohexene, 3-methyl-1-cyclohexene, 4-methyl-1-cyclohexene. There is a very little chance that the fourth one can be found. The forth would be methylenecyclohexane.
c) The major product is 4-methyl-1-cyclohexene. The mole fraction of the major product is 0.79 [The % compositions are: 81.4 (4-methyl-1-cyclohexene), 10.4 (3-methyl-1-cyclohexene), 8.45 (1-methyl-1-cyclohexene), 1.96 (methylenecyclohexane)].
Mole fraction of major is = no. of moles of major product/ total number of moles.
d) It requires two hydride shifts for the carbocation to attain the most stable (tertiary) status and since the conjugate base of the phosphoric acid is a strong, it continuously tries to abstract the proton and hence the carbcation tries to settle by the formation of a double bond.
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