Quiz!
Note:
Although the questions are in English, you may answer them in Dutch.
The table below summarises energy-differences between axial and equatorial conformations for some alkylcylcohexanes. What is the reason for the big increase at
tert
-butylcyclohexane (look at the models)?
molecule
energy difference (equatorial - axial) in kJ/mole
methylcyclohexane
6.17
ethylcyclohexane
6.11
isopropylcyclohexane
7.65
tert
-butylcyclohexane
19.52
methyl, equatorial
methyl, axial
ethyl, equatorial
ethyl, axial
isopropyl, equatorial
isopropyl, axial
tert
-butyl, equatorial
tert
-butyl, axial
In 1,2-dimethylcyclohexane, the methyl groups can occupy the axial and equatorial positions in three combinations: axial/axial, axial/equatorial, and equatorial/equatorial. (In the next chapter we will discuss the stereochemistry of these compounds).
Calculate the energies of these three combinations. Use the molecule editor with
cyclohexane
(it will pop up in a separate window). Substitute the appropriate hydrogens by methyl, press "continue" twice, and wait for the result to appear.
Type the Heat of Formation (HoF) values, listed as "rel. energy" in the output, in the area below, and please remember that -200 is lower than -190!
Are the values in the relative order you expect? Explain!
HoF axial/axial: HoF axial/equatorial: HoF equatorial/equatorial:
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and
the answers!
