9 topics with a brief review: definitions, key facts, and classroom questions.
This section focuses on oxygen-containing organic compounds, which form the structural basis of major metabolites and most pharmaceutical drugs. Here, we thoroughly analyze the chemistry of alcohols and phenols, aldehydes and ketones, as well as carboxylic acids and their esters. Special emphasis is placed on heterofunctional organic acids and their derivatives—molecules containing multiple different functional groups, which is critical for understanding biochemical processes in the body.
During practical classes and colloquia, instructors most frequently ask about the mechanisms of nucleophilic addition to the carbonyl group, esterification reactions, and the specific acid-base properties of phenols. Be prepared to explain how the mutual influence of atoms in molecules of heterofunctional acids (e.g., hydroxy or keto acids) determines their specific reactivity in vivo and in vitro.
Why are the boiling points of alcohols much higher than those of hydrocarbons of similar mass?
Alcohols contain a polar hydroxyl group and hydrogen bonds that strongly attract molecules to each other. In non-polar hydrocarbons, intermolecular interaction is very weak.
Why do ethanol and dimethyl ether have completely different boiling points despite having the same molecular formula?
Ethers lack intermolecular hydrogen bonds, so significantly less energy is required to vaporize them. Ethanol boils at 78 °C, whereas dimethyl ether boils at -24.8 °C.
Why is phenol referred to as carbolic acid if it does not belong to the class of carboxylic acids?
This is a historical trivial name reflecting its acidic nature. Due to the conjugation of the hydroxyl group with the ring, phenol readily dissociates a proton to form salts, surpassing certain inorganic acids in strength (e.g., orthosilicic acid).
What is the main structural difference between an aldehyde and a ketone?
In aldehydes, the functional group $-CHO$ is always located at the end of the carbon chain and bonded to a hydrogen atom. In ketones, the carbonyl group $C=O$ is situated between two hydrocarbon radicals.
Why are nucleophilic addition reactions atypical for carboxylic acids?
The presence of the hydroxyl group blocks this pathway. Following nucleophilic addition, the elimination of a water molecule would be required, which is energetically highly unfavorable. Therefore, substitution reactions proceed instead.
Where does the oxygen come from when water is formed in the esterification reaction?
The oxygen in the eliminated water molecule originates from the carboxyl group of the acid, which was proven by the oxygen-18 isotope experiment.
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