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StudentNotesSection13 - Section 13: Alcohols, Phenols,...

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Section 13: Alcohols, Phenols, Ethers and Epoxides 179 Section 13: Alcohols, Phenols, Ethers and Epoxides 13.1 Nomenclature and Properties of Alcohols & Phenols 13.1.1 Nomenclature Alcohols and phenols contain a hydroxyl (-OH) group. In alcohols, this group is attached to an alkyl chain; in phenols the group is attached directly to an aromatic ring. In a manner similar to alkyl halides, alcohols may be classified as primary, secondary or tertiary. This is based on the number of groups attached to the carbon atom directly attached to the hydroxyl group The nomenclature of alcohols is surprisingly straightforward – the hydroxyl group has priority (of the groups considered thus far). The parent chain is the chain which includes the hydroxyl group – the –e suffix of the parent name alkane is replaced by –ol.
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Section 13: Alcohols, Phenols, Ethers and Epoxides 180 13.1.2 Physical Properties Alcohols and phenols contain a hydroxyl group that is capable of forming hydrogen-bonded complexes with other alcohol or phenol molecules. They tend to have relatively high boiling points (or higher than expected), and the smaller alcohols are water miscible . It should be noted that the effect on water solubility (and the difference between the boiling points of alcohols, and, say alkyl halides) is diminished with increasing length of the alcohol chain, and the degree of substitution around the carbon attached to the hydroxyl group. The latter effect can be thought of as a combination of hydrophobicity and steric demand near the hydroxyl group. 13.1.3 Acidity and Basicity of Alcohols Alcohols and phenols may be considered to be organic analogues of water, and under the right conditions, may act as a Brønsted acid or base.
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Section 13: Alcohols, Phenols, Ethers and Epoxides 181 We can measure the pK A constants for alcohols and phenols in water. Alcohol pK A Phenol pK A tert -butanol 18.0 p -aminophenol 10.46 isopropanol 17.0 p -methoxyphenol 10.21 ethanol 16.0 p -methylphenol 10.17 water 15.7 phenol 9.89 methanol 15.5 p -chlorophenol 9.38 2,2,2-trifluoroethanol 12.4 p -bromophenol 9.35 nonafluoro-tert-butanol 5.4 p -nitrophenol 7.15 2,4,6-trinitrophenol (picric acid) 0.60
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Section 13: Alcohols, Phenols, Ethers and Epoxides 182 We note that once again, the phenoxide anion may be stabilized by the presence of electron withdrawing groups. Thus, p -nitrophenol ( pK A = 7.15) is more acidic than p - methylphenol ( p K A = 10.17). N O O OO O H 3 C no resonance stabilization inductive and resonance stabilization N O O O 13.2 Preparation of Alcohols & Phenols 13.2.1 Preparation of Alcohols from Alkenes As we know from earlier discussions, alcohols may be prepared from alkenes via a number of methods: Treatment of the alkene with borane, followed by oxidation with basic peroxide. 1. BH 3 /THF 2. H 2 O 2 , HO - /H 2 O OH Treatment of the alkene with mercuric acetate, with reductive cleavage of the resultant organomercuric compound with sodium borohydride.
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StudentNotesSection13 - Section 13: Alcohols, Phenols,...

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