Molecular Structure and Properties
The epoxy cycle of ethylene oxide is an almost regular triangle with bond angles of about 60° and a significant angular stress corresponding to the energy of 105 kJ/mol. For comparison, in alcohols the C–O–H angle is about 110°; in ethers, the C–O–C angle is 120°. The moment of inertia about the principal axes are IA = 32.921×10−40 g·cm², IB = 37.926×10−40 g·cm² and IC = 59.510×10−40 g·cm². The dipole moment at a temperature in the range 17–176 °C is 6.26×10−30 C·m.
The relative instability of the carbon-oxygen bonds in the molecule is revealed by the comparison in the table of the energy required to break two C–O bonds in the ethylene oxide or one C–O bond in ethanol and dimethyl ether:
| Reaction | ΔH°298, kJ/mol | Method |
|---|---|---|
| (C2H4)O → C2H4 + O (cleavage of two bonds) | 354.38 | Calculated, from atomic enthalpies |
| C2H5OH → C2H5 + OH (breaking one bond) | 405.85 | Electron impact |
| CH3OCH3 → CH3O + CH3 (breaking one bond) | 334.72 | Calculated using enthalpies of radicals formation |
This instability determines the chemical activity of ethylene oxide and explains the ease of opening its cycle in addition reactions (see Chemical properties).
Read more about this topic: Ethylene Oxide
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