Alcohol

Alcohol concept：

  Alcohol refers to a compound formed by linking a hydroxyl group to an aliphatic hydrocarbon group; The hydroxyl group is attached to the benzene ring, and it is classified as a phenol because its chemical properties are different from ordinary alcohols; The hydroxyl group is attached to the sp2. hybrid double-bonded carbon atom and belongs to the enol group, which is mostly unable to exist stably because of its tautomerization into ketone.Important alcohols are: methanol, ethanol, benzyl alcohol, ethylene glycol, etc.

Classification, structure and physical properties of alcohols：

   1. Classification of alcohols According to the classification of the carbon atoms connected by the hydroxyl group, the alcohol with the hydroxyl group attached to the primary carbon atom is called the primary alcohol, also known as the primary alcohol; An alcohol with a hydroxyl group attached to a secondary carbon atom is called a secondary alcohol, also known as a secondary alcohol; An alcohol with a hydroxyl group attached to a tertiary carbon atom is called a tertiary alcohol, also known as a tertiary alcohol. The alcohol attached to the unsaturated carbon atom by the hydroxyl group is very unstable and is called enol, which will soon isomerize into aldehydes and ketones.

   2. The melting and boiling points of alcohols The melting and boiling points of lower alcohols are much higher than those of hydrocarbons with the same number of carbon atoms, because there are hydrogen bonding associations between alcohol molecules. When the alcohol is in the solid state, the association is relatively strong, and in the liquid state, after the hydrogen bond is broken, it will be formed again, but in the gas phase or in the dilute solution of non-polar solvents, the alcohol molecules are far from each other, and the individual alcohol molecules can exist independently. The intermolecular hydrogen bonds increase with increasing concentration, while the intramolecular hydrogen bonds are not affected by the concentration.

   3. The structure of alcohol In general, the two largest groups on the adjacent two carbon atoms are in the most stable in the cross-conformation, which is the dominant conformation, and when these two groups may be associated with hydrogen bonds, the stability of the molecule can be increased due to the formation of hydrogen bonds. The two 

Acidity and alkalinity of alcohol

   1.The acidity and alkalinity of acid alcohols are related to the electronic effect of the hydrocarbon groups attached to oxygen, and the stronger the electron-absorbing ability of the hydrocarbon groups, the weaker the alkalinity and the stronger the acidity of the alcohol. On the contrary, the stronger the electron-donor ability of the hydrocarbon group, the more basic and less acidic the alcohol. The steric hindrance of the hydrocarbon group also has an effect on the acidity and alkalinity of the alcohol, so it is important to analyze the electronic effect and steric hindrance of the hydrocarbon group

Alcohol properties：

  Generally, alcohols are colorless liquids or solids, unary n-carbon alcohols containing less than 12 carbon atoms are liquids, 12 or more are solids, and polyols (such as glycerol) are syrupy substances. Monoalcohols are soluble in organic solvents, and alcohols below three carbons are soluble in water. The melting and boiling points of lower alcohols are much higher than those of hydrocarbons with the same number of carbon atoms, which is due to the presence of hydrogen bonds in the alcohol molecule, and association occurs. Saturated alcohols do not discolor bromine water. Alcohols are chemically active, and the carbon-oxygen bonds and hydrogen-oxygen bonds in the molecule are both polar bonds. With the hydroxyl group as the center, two types of reactions can be carried out: hydrogen-oxygen bond cleavage and carbon-oxygen bond cleavage. In addition, carbon atoms attached to hydroxyl groups are susceptible to oxidation to form aldehydes, ketones, or acids.