There are two types of oxygen-containing organic compounds. In some cases, when they contain the same number of carbon atoms, they have the same molecular formula, but different structures. They belong to functional group isomers of each other. These two types of compounds are alcohols and ethers.
How is Alcohols Classified?
Compounds in which hydrogen atoms in aliphatic hydrocarbon molecules or hydrogen atoms on aromatic hydrocarbon side chains are replaced by hydroxyl groups are called alcohols. Hydroxyl is the functional group of alcohols.
Alcohols can be classified according to the number of hydroxyl groups contained in the molecule. Alcohols containing one hydroxyl group are called monohydric alcohols, those containing two hydroxyl groups are called dihydric alcohols, and alcohols with more than two hydroxyl groups are collectively called polyhydric alcohols. Alcohols can also be classified according to the level of the carbon atom to which the hydroxyl group is connected. Alcohols with hydroxyl groups connected to the primary carbon atom are called primary alcohols; alcohols with hydroxyl groups connected to the secondary carbon atom are called secondary alcohols; and alcohols with hydroxyl groups connected to the tertiary carbon atom are called tertiary alcohols.
What are the Physical Properties of Alcohols?
Some monohydric saturated alcohols are colorless neutral liquids with a special smell and spicy taste. Water and alcohols both have hydroxyl groups and can form hydrogen bonds with each other. According to the rule that like dissolves like, methanol, ethanol and propanol can be dissolved in water in any proportion; alcohols with 4 to 11 carbons are oily liquids and can only be partially soluble in water. As the relative molecular mass increases, the influence of the alkyl group on the entire molecule becomes greater and greater, making the physical properties of higher alcohols similar to those of alkanes. Although the density of monohydric saturated alcohols is greater than that of the corresponding alkanes, it is still lighter than water.
What are the Typical Reactions of Alcohols?
Reaction of alcohols with oxygen-containing inorganic acids
Alcohols react with oxygen-containing inorganic acids to lose a molecule of water and form inorganic acid esters. For example: The reaction process of alcohol and nitric acid is as follows: the alcohol molecule acts as a nucleophile to attack the positively charged part of the acid or its derivative, the nitrogen-oxygen double bond opens, and then the hydrogen-oxygen bond of the alcohol molecule breaks, and the nitric acid part loses a molecule of water to re-form the nitrogen-oxygen double bond, for example:
Displacement reaction of alcohol hydroxyl
Generally, hydrohalic acid reacts with alcohol to form halogenated hydrocarbons, and the alcohol hydroxyl group is replaced by a halogen atom in the reaction,
Oxidation reaction of alcohol
Primary alcohols and secondary alcohols have hydrogen on the carbon atom connected to the alcohol hydroxyl group, which can be oxidized to aldehydes, ketones or acids; tertiary alcohols have no hydrogen on the carbon atom connected to the alcohol hydroxyl group, and are not easily oxidized. For example, under acidic conditions, they are easily dehydrated to olefins, and then the carbon-carbon bond is oxidized and broken to form small molecular compounds. For example, secondary alcohols are oxidized to ketones:
How is Ethers Classified?
Compounds in which both hydrogen atoms in a water molecule are replaced by hydrocarbon groups are called ethers. Ether compounds all contain ether bonds (C-O-C).
Ethers with the same two hydrocarbon groups are called symmetrical ethers, also called simple ethers. Ethers with different hydrocarbon groups are called asymmetrical ethers, also called complex ethers.
According to the types of the two hydrocarbon groups, ethers can also be divided into aliphatic ethers and aromatic ethers.
In aliphatic ethers, ethers without rings in the molecule are called acyclic ethers. They can also be further divided into saturated ethers and unsaturated ethers. Ethers with hydrocarbon groups forming a ring are called cyclic ethers. Ethers containing oxygen on the ring are called inner ethers or epoxy compounds. Large ring ethers containing multiple oxygens are called crown ethers because they are shaped like a crown.
What are the Physical Properties of Ethers?
Most ethers are volatile and flammable liquids. Unlike alcohols, ether molecules cannot form hydrogen bonds, so their boiling points are much lower than those of alcohols of the same composition. For example, the boiling point of ethanol is 78.4℃, and the boiling point of methyl ether is -24.9℃; the boiling point of n-butanol is 117.8℃, and the boiling point of ethyl ether is 34.6℃.
Most ethers are insoluble in water, but commonly used tetrahydrofuran and 1,4-dioxane are completely miscible with water because they easily form hydrogen bonds with water. Although the number of carbon and oxygen atoms in ether is the same as that in tetrahydrofuran, the latter's oxygen and carbon frame together form a ring, which is easy to form hydrogen bonds with water, while the oxygen atoms in ether are difficult to form hydrogen bonds with water, so ether is only slightly soluble in water.
What are the Typical Reactions of Ether?
Oxidation reaction of ether
If ether and other ethers are often in contact with air or exposed to light, they can generate non-volatile peroxides (peroxides), such as:
Carbon-oxygen bond cleavage reaction of ether
The carbon-oxygen bond breaks when ether is heated with hydroiodic acid. This cleavage is the reaction of acid and ether, and then, depending on the nature of the alkyl group, SN1 or SN2 reaction occurs. Primary alkyl groups undergo SN2 reactions, while tertiary alkyl groups easily undergo SN1 reactions to generate iodoalkanes and alcohols. In the presence of excess acid, the alcohol produced is also converted into iodoalkanes, such as:
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