12.2 Properties of Alcohols | Organic Chemistry

This paragraph introduces the topic of alcohol properties, focusing on solubility in water, boiling points, and acidity. It explains how the hydroxyl group's ability to form hydrogen bonds significantly influences these properties. As the carbon chain in alcohols lengthens, solubility in water decreases due to the increasing hydrophobicity. The paragraph also compares the boiling points of alcohols to similar molecular weight compounds, highlighting that alcohols have higher boiling points due to stronger intermolecular forces. Lastly, it touches on the acidity of alcohols, which is influenced by the electronegativity of oxygen and the solubility of the conjugate base in water.

The second paragraph delves into the acidity of alcohols, noting a trend where secondary and tertiary alcohols are less acidic than primary alcohols. It emphasizes the role of solubility in water for the conjugate base in determining acidity. The discussion then shifts to phenols, which are more acidic than typical alcohols due to resonance stabilization of the conjugate base, the phenoxide ion. The paragraph also explains the concept of ortho, meta, and para positions relative to a functional group on a benzene ring and how they relate to the acidity of phenols.

This paragraph explores how different groups attached to a phenol can alter its acidity. It categorizes these groups into electron-donating and electron-withdrawing groups, each with varying strengths. Electron-withdrawing groups increase the acidity of phenols by stabilizing the conjugate base, while electron-donating groups have the opposite effect. The paragraph also discusses the significance of the position of these groups, with the ortho and para positions having the greatest impact due to resonance effects. It concludes by introducing the concept of strong electron-withdrawing groups like carbonyl, nitro, and cyano groups, which have an even more pronounced effect on acidity.

The fourth paragraph provides a deeper understanding of electron-donating and withdrawing groups, particularly in the context of conjugated systems. It explains that groups like alkyl or aryl, as well as nitrogen or oxygen with lone pairs, can donate electrons through resonance, making them electron-donating groups. In contrast, groups with a positive formal charge or those attached to electronegative atoms are electron-withdrawing. The paragraph also clarifies that the impact of these groups depends on their position relative to the functional group and the nature of the conjugated system involved.

This paragraph guides through the process of ranking the acidity of phenols with different substituents. It explains that electron-withdrawing groups make phenols stronger acids, while electron-donating groups make them weaker. The position of the substituent on the phenol ring is also crucial, with the ortho position having the most significant impact. The paragraph outlines how to identify and categorize substituents as either donating or withdrawing and uses this information to rank the acidity of four example phenols provided in the study guide.

The final paragraph discusses the practical aspect of deprotonating alcohols and phenols to form alkoxides and phenoxides, respectively. These negatively charged species are strong nucleophiles and bases, which are useful in organic synthesis, such as in SN2 reactions. The paragraph explains that phenols, being more acidic, can be deprotonated with sodium hydroxide, while alcohols require stronger bases like sodium hydride or metallic sodium or potassium. It also mentions the irreversibility of these reactions due to the formation of hydrogen gas and encourages viewers to like, share, and ask questions for further clarification.