Structure of alcohol

The melting and boiling points of lower alcohols are much higher than those of hydrocarbons with the same number of carbon atoms, which is the result of hydrogen bond association between alcohol molecules. The experimental results show that it takes about 21 to 30KJ/mol for the hydrogen bond to break, which indicates that it is much weaker than interatomic (105 to 418KJ/mol). Alcohol in solid state, the association is more firm; In the liquid state, the hydrogen bond will re-form after it is broken; However, in dilute solutions of gaseous or non-polar solvents, alcohol molecules are far apart from each other, and each alcohol molecule can exist separately. There are more than two positions in the polyol molecule that can form hydrogen bonds, so the boiling point is higher, such as the boiling point of ethylene glycol at 197 ° C. The intermolecular hydrogen bond increases with the increase of concentration, but the intramolecular hydrogen bond is not affected by the concentration.
Methanol is taken as an example to illustrate the structure of alcohols. In the methanol molecule, the bond length of the carbon-oxygen bond is 143pm, and the bond Angle of ∠COH is 108.9°. It is generally believed that the oxygen atom in the alcohol hydroxyl group is sp³ unequal hybrid, and the 6 electrons in the outermost layer of the oxygen atom are distributed in 4 sp³ hybrid orbitals, of which 2 sp³ orbitals containing single electrons form carbon-oxygen bonds with carbon atoms and hydrogen atoms, respectively. The remaining two pairs of unshared electrons occupy the other two sp³ orbitals. The hydrogen-oxygen bond and the two pairs of unshared electrons on oxygen are in a cross-dominant conformation with the three C-H bonds of the methyl group.