We are asked to determine the major factors responsible for the difference in boiling points of the two ethers:
Recall that there are several types of intermolecular forces (IMF):
1. Ion-dipole interaction – occurs between an ion and a polar covalent compound; strongest IMF
2. Hydrogen bonding – occurs in compounds where hydrogen is directly connected to an electronegative element such as N, O, or F; 2nd strongest IMF
3. Dipole-dipole interaction – occurs between two polar covalent compounds; 3rd strongest IMF
4. Dispersion forces – occurs in all compounds and is the primary IMF exhibited by nonpolar compounds; weakest IMF
Ethylene glycol (HOCH2CH2OH), the major substance in antifreeze, has a normal boiling point of 198 oC. By comparison, ethyl alcohol (CH3CH2OH) boils at 78 oC at atmospheric pressure. Ethylene glycol dimethyl ether (CH3OCH2CH2OCH3) has a normal boiling point of 83 oC, and ethyl methyl ether (CH3CH2OCH3) has a normal boiling point of 11 oC.
What are the major factors responsible for the difference in boiling points of the two ethers?