17: Alcohols and Phenols
- Page ID
- 448722
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)When you have completed Chapter 17, you should be able to
- fulfill all of the detailed objectives listed under each individual section.
- design a multi‑step synthesis using any of the reactions introduced in this chapter, together with any number of the reactions discussed in Chemistry 350.
- solve “road‑map” problems that require a knowledge of the chemistry of alcohols and phenols, in addition to the chemistry of the other classes of compounds discussed in Chemistry 350.
- define, and use in context, the key terms introduced in this chapter.
In this chapter, we examine the chemistry of the alcohol family of compounds. Alcohols can undergo a wide variety of reactions, and because of this reactivity and because they can be prepared in a number of different ways, alcohols occupy an important position in organic chemistry.
The discussion begins with an outline of the nomenclature of alcohols and phenols. We review the physical properties of these compounds, and discuss methods used to obtain the lower members of the series on an industrial scale. A detailed discussion of the laboratory preparation of alcohols follows, with particular emphasis on those methods that involve either the reduction of a carbonyl compound or the use of a Grignard reagent.
Certain reactions of alcohols were discussed in previous chapters. In this chapter, we concentrate on the oxidation of alcohols to carbonyl compounds. We also introduce the concept of protecting a sensitive functional group during an organic synthesis. The discussion then turns to the uses of phenols, their preparation and their chemical reactivity.
Infrared, nuclear magnetic resonance and mass spectroscopy each can provide valuable information about alcohols and phenols, and we illustrate the application of these techniques to the identification of unknown alcohols and phenols with a number of examples.
- 17.0: Why This Chapter?
- Alcohols and phenols can be thought of as organic derivatives of water in which one of water’s hydrogens is replaced by an organic group: H–O–H versus R–O–H and Ar–O–H. In practice, the name alcohol is restricted to compounds that have their –OH group bonded to a saturated, sp³-hybridized carbon atom, while compounds with their –OH group bonded to a vinylic, sp²-hybridized carbon are called enols.
- 17.1: Naming Alcohols and Phenols
- Alcohols are classified as primary (1°), secondary (2°), or tertiary (3°), depending on the number of organic groups bonded to the hydroxyl-bearing carbon.
- 17.2: Properties of Alcohols and Phenols
- Alcohols and phenols have nearly the same geometry around the oxygen atom as water. The R–O–H bond angle has an approximately tetrahedral value (108.5° in methanol, for instance), and the oxygen atom is sp³-hybridized.
- 17.3: Preparation of Alcohols- A Review
- Alcohols are considered on of the more important functional groups in organic chemistry. They can be prepared from compounds containing a wide assortment of functional groups. Also, the can be used to create compounds with a wide variety of functional groups such as: alkenes, ketones, carboxylic acids, and others. Many functional group conversions can be accomplished through the preparation of an alcohol giving them an important central position in organic synthesis.
- 17.4: Alcohols from Carbonyl Compounds - Reduction
- The most general method for preparing alcohols, both in the laboratory and in living organisms, is by reduction of a carbonyl compound. Just as reduction of an alkene adds hydrogen to a C=C bond to give an alkane, reduction of a carbonyl compound adds hydrogen to a C=O bond to give an alcohol. All kinds of carbonyl compounds can be reduced, including aldehydes, ketones, carboxylic acids, and esters.
- 17.5: Alcohols from Carbonyl Compounds - Grignard Reagents
- Grignard reagents (RMgX), prepared by reaction of organohalides with magnesium (Section 10.6), react with carbonyl compounds to yield alcohols in much the same way that hydride reducing agents do. Just as carbonyl reduction involves addition of a hydride ion nucleophile to the C=O bond, Grignard reaction involves addition of a carbanion nucleophile.
- 17.6: Reactions of Alcohols
- We’ve already seen several reactions of alcohols—their conversion into alkyl halides and tosylates in Section 10.5 and their dehydration to give alkenes in Section 8.1—albeit without mechanistic details.
- 17.7: Oxidation of Alcohols
- Perhaps the most valuable reaction of alcohols is their oxidation to give carbonyl compounds—the opposite of the reduction of carbonyl compounds to give alcohols. Primary alcohols are oxidized either to aldehydes or carboxylic acids, and secondary alcohols are oxidized to ketones, but tertiary alcohols don’t normally react with most oxidizing agents.
- 17.8: Protection of Alcohols
- It often happens, particularly during the synthesis of complex molecules, that one functional group in a molecule interferes with an intended reaction on another functional group elsewhere in the same molecule. We saw earlier in this chapter, for instance, that a Grignard reagent can’t be prepared from an alcohol-containing halidel because the C–Mg bond is not compatible with the presence of an acidic –OH group in the same molecule.
- 17.9: Phenols and Their Uses
- The outbreak of World War I provided a stimulus for the industrial preparation of large amounts of synthetic phenol, which was needed as a raw material to manufacture the explosive, picric acid (2,4,6-trinitrophenol). Today, approximately 132 million tons of phenol is manufactured worldwide each year for use in such products as Bakelite resin and adhesives for binding plywood.
- 17.10: Reactions of Phenols
- The hydroxyl group is a strongly activating, ortho- and para-directing substituent in electrophilic aromatic substitution reactions. As a result, phenols are highly reactive substrates for electrophilic halogenation, nitration, sulfonation, and Friedel–Crafts reactions.
- 17.11: Spectroscopy of Alcohols and Phenols
- The section on spectroscopy of alcohols and phenols discusses how these compounds are characterized using infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy. It highlights the distinct IR absorption peaks associated with hydroxyl (-OH) groups and how NMR can provide insights into the structure of alcohols and phenols through chemical shifts and splitting patterns. These techniques are essential for identifying functional groups and understanding the molecular environment.
- 17.12: Chemistry Matters—Ethanol- Chemical, Drug, and Poison
- The section discusses ethanol as a significant chemical in both recreational and medicinal contexts. It highlights ethanol's role as a central nervous system depressant, its therapeutic uses, and potential toxicity at high levels. The effects of ethanol consumption, such as impairment and addiction, are also noted, alongside its classification as a drug and poison. Understanding ethanol's chemical properties and biological effects is crucial for its safe use.
- 17.14: Summary
- This summary highlights the key features of alcohols and phenols, including their structures, properties, and classifications. It discusses how alcohols can be primary, secondary, or tertiary based on their carbon bonding. The reactivity of alcohols, their role in various reactions, and their importance in biological systems are also emphasized. Phenols are noted for their distinct properties and applications.
- 17.15: Summary of Reactions
- This section summarizes the key reactions of alcohols and phenols, including oxidation, dehydration, and substitution reactions. Alcohols can be converted into alkyl halides and ethers, while phenols can undergo electrophilic aromatic substitution. Additionally, alcohols can be oxidized to aldehydes or ketones and then to carboxylic acids. The synthesis and reactivity of these compounds illustrate their importance in organic chemistry and biochemistry.