Chemistry 2100 Chapter 14

ALCOHOLS ETHERS THIOLS

alcohol ether thiol / mercaptan (sulfhydryl)

Common Nomenclature IUPAC Nomenclature • dialkyl "ether" • alkyl "alcohol" • "e" "ol" • locator numbers

Alcohols Alcohol: A compound that contains an -OH (hydroxyl) group bonded to a tetrahedral carbon. Methanol, CH3OH, is the simplest alcohol. Nomenclature 1. Select the longest carbon chain that contains the -OH group as the parent alkane and number it from the end that gives the -OH the lower number. 2. Change the ending of the parent alkane from -e to -ol and use a number to show the location of the -OH group; for cyclic alcohols, the carbon bearing the -OH group is carbon-1. 3. Name and number substituents and list them in alphabetical order.

Nomenclature In the IUPAC system, a compound containing two hydroxyl groups is named as a diol, one containing three hydroxyl groups as a triol, and so forth. IUPAC names for diols, triols, and so on retain the final "-e" in the name of the parent alkane. We commonly refer to compounds containing two hydroxyl groups on adjacent carbons as glycols.

Physical Properties Alcohols are polar molecules. The C-O and O-H bonds are both polar covalent.

Physical Properties In the liquid state, alcohols associate by hydrogen bonding.

boiling points (°C) CH3OH 65° CH3CH2CH2OH 97° CH3CH3 -88° CH3CH2CH2CH3 0° CH3Cl -24° CH3CH2CH2Cl 46° PhOH 182° CH3CH2CH2CH2OH 118° PhCH3 110° (CH3)2CHCH2OH 108° PhCl 132° (CH3)3COH 83°

solubility (g / 100 mL H2O) CH3CH2OH CH3CH2CH2OH CH3CH2CH2CH2OH CH3CH2CH2CH2CH2OH CH3CH2CH2CH2CH2CH2OH CH3CH2CH2CH2CH2CH2CH2CH2OH CH3CH2OCH2CH3 (CH3)2CHCH2OH (CH3)3COH C6H11OH ∞ 8.3 2.4 0.6 0.05 7.8 10.0 3.6

Acidity of Alcohols Alcohols have about the same pKa values as water. Aqueous solutions of alcohols have the same pH as that of pure water. Alcohols and phenols both contain an OH group. Phenols are weak acids and react with NaOH and other strong bases to form water-soluble salts. Alcohols are weaker acids than phenols and do not react in this manner. n

Preparing Alcohols Fermentation Alkene Hydration H H H H H H H H zymase sucrose ethanol Alkene Hydration H H H H H H H H

Dehydration

Oxidation of Alcohols (1°) (2°)

Ethers

Common Nomenclature IUPAC Nomenclature • dialkyl "ether" • dialkyl "ether" • "alkoxy"

Physical Properties Ethers are polar molecules in which oxygen bears a partial negative charge and each carbon bonded to it bears a partial positive charge.

Physical Properties However, only weak forces of attraction exist between ether molecules in the pure liquid. Consequently, boiling points of ethers are close to those of hydrocarbons of similar molecular weight. Ethers have lower boiling points than alcohols of the same molecular formula.

Reactions of Ethers Ethers resemble hydrocarbons in their resistance to chemical reaction. They do not react with oxidizing agents such as potassium dichromate. They do not react with reducing agents such as H2 in the presence of a transition metal catalyst or with hydride reducing agents such as NaBH4. They are not affected by most acids or bases at moderate temperatures. Because of their general inertness and good solvent properties, ethers, such as diethyl ether and THF, are excellent solvents in which to carry out organic reactions.

pentane bp 36°C (diethyl) ether bp 36°C 7.8 g/100 mL 1-butanol bp 118°C 8.3 g/100 mL

Anesthetics

p. 409

Thiols

Thiols Thiol: A compound containing an -SH (sulfhydryl group). The most outstanding property of low-molecular-weight thiols is their stench. They are responsible for smells such as those from rotten eggs and sewage. The scent of skunks is due primarily to these two thiols.

Naming thiols Alkane + thiol 1-propanethiol 2-propene-1-thiol

Physical Properties Because of the small difference in electronegativity between sulfur and hydrogen (2.5 - 2.1 = 0.4), an S-H bond is nonpolar covalent. Thiols show little association by hydrogen bonding. Thiols have lower boiling points and are less soluble in water and other polar solvents than alcohols of similar molecular weight.

CH3CH2OH (bp 78°C) CH3OCH3 (bp -24°C) CH3CH2SH (bp 35°C) CH3SCH3 (bp 37°C)

Oxidation sulfide (thioether) sulfoxide sulfone

cysteine

-helix

-helix -helix

-helix -helix

-helix -helix

-helix -helix -pleated sheet

-pleated sheet -helix -helix -pleated sheet

-pleated sheet -helix salt bridge -helix -pleated sheet

-pleated sheet -helix salt bridge -helix hydrogen bond -pleated sheet

-pleated sheet -helix hydrogen bond salt bridge -helix hydrogen bond -pleated sheet

hydrophilic interaction to water -pleated sheet -helix hydrogen bond salt bridge -helix hydrogen bond -pleated sheet

hydrophilic interaction to water -pleated sheet -helix hydrogen bond hydrophobic interaction salt bridge -helix hydrogen bond -pleated sheet

hydrophilic interaction to water -pleated sheet -helix hydrogen bond hydrophobic interaction salt bridge -helix hydrogen bond -pleated sheet

hydrophilic interaction to water -pleated sheet -helix hydrogen bond hydrophobic interaction salt bridge disulfide bond -helix hydrogen bond -pleated sheet