Alcohols, Ethers, Thiols and Chirality Chemistry 20 Chapters 5 & 6 Alcohols, Ethers, Thiols and Chirality

Alcohols Alcohols Contain a hydroxyl group (-OH). Phenols Contain a benzene ring with a hydroxyl group (-OH). OH

Naming Alcohols IUPAC name: We replace the -e in alkane name with -ol. Common name: As simple alcohols using the name of the alkyl group followed by “alcohol”. CH4 methane CH3─OH methanol (methyl alcohol) CH3─CH3 ethane CH3─CH2─OH ethanol (ethyl alcohol)

Naming Alcohols Step 1 Step 2 Step 3 Step 4 Select the longest carbon chain that contains the -OH group. Step 2 Number from the end nearest -OH group. Step 3 Change the ending of parent alkane from -e to -ol. Use the number to show the location of -OH. Step 4 Give the location and number of each substituent (alphabetical order) as a prefix to the name of the main chain.

Naming Alcohols CH3─CH2─CH2─OH 1-propanol OH │ CH3─CH─CH3 2-propanol │ │ CH3─CH─CH2─CH2─CH─CH3 5-methyl-2-hexanol 3 2 1 3 2 1 6 5 4 3 2 1

Naming Alcohols OH │ CH3─CH─CH2─CH3 2-butanol CH3 CH3─CH─CH ─CH2─OH 3-chloro-2-methyl-1-butanol CH3─C─CH2─OH 2,2-dimethyl-1-propanol 1 2 3 4 Cl 4 3 2 1 CH3 3 2 1

Diols & Triols Diol: a compound containing two –OH (Hydroxyl groups). Triol: a compound containing three –OH (Hydroxyl groups). CH2 – CH2 CH3 – CH – CH2 CH2 – CH – CH2 OH OH OH OH OH OH OH 1,2-Ethanediol (Ethylene glycol) 1,2-Propanediol (Propylene glycol) 1,2,3-Propanetriol (glycerol, glycerin)

Different types of Alcohols Primary (1º) Secondary (2º ) Tertiary (3º) H CH3 CH3 │ │ │ CH3─C─OH CH3─C─OH CH3─C─OH H H CH3 1 C 2 C 3 C attached attached attached to C-OH to C-OH to C-OH

Phenol Phenol is the IUPAC name for benzene with a hydroxyl group. OH Many are used as antiseptics and disinfectants. Is a weak acid. OH Phenol

Physical Properties of Alcohols Alcohols are polar molecules (because of O-H and C-O). Hydrogen bonding between alcohols molecules. Have higher boiling points than Alkanes, Alkenes, and Alkynes. Molecular weight ↑ : London dispersion forces ↑ : bp ↑ More soluble in water (Molecular weight ↑ : solubility ↓). They are weak acids (weaker than Phenol). polar nonpolar OH

Chemical Properties of Alcohols 1. Acidity of Alcohols: 2. Acid-Catalyzed Dehydration: H2SO4 CH3CH2OH CH2 = CH2 + H2O 180°C Dehydration - C – C - C = C + H20 Hydration H OH 3. Oxidation of Alcohols:

Acid-Catalyzed Dehydration H2SO4 1° CH3CH2OH CH2 = CH2 + H2O High T 180°C OH H2SO4 CH3CHCH3 CH2 = CH - CH2 + H2O 2° Moderate T 140°C OH H2SO4 3° CH3 C CH3 CH3 C = CH2 + H2O Low T 50°C CH3 CH3 1° 2° 3° Ease of dehydration of alcohols

Acid-Catalyzed Dehydration Alkene having the greater number of alkyl groups on the double bond generally predominates.

Oxidation of 1° Alcohols In the oxidation [O] of a primary alcohol 1, one H is removed from the –OH group and another H from the C bonded to the –OH. primary alcohol aldehyde OH O │ ║ CH3─C─H CH3─C─H + H2O │ H ethanol ethanal (ethyl alcohol) (acetaldehyde) [O] K2Cr2O7 H2SO4

Oxidation of 2° Alcohols The oxidation of 2 alcohols is similar to 1°, except that a ketone is formed. secondary alcohol ketone OH O │ ║ CH3─C─CH3 CH3─C─CH3 + H2O │ H 2-propanol 2-propanone [O] K2Cr2O7 H2SO4

Oxidation of 3° Alcohols Tertiary 3 alcohols cannot be oxidized. Tertiary alcohol no reaction OH │ CH3─C─CH3 no product CH3 no H on the C-OH to oxidize 2-methyl-2-propanol [O] K2Cr2O7 H2SO4

Oxidation of Alcohols in our body In the body: Enzymes in the liver oxidize ethanol. Blood alcohol over 0.4% can be fatal. O O ║ ║ CH3CH2OH CH3CH CH3COH 2CO2 + H2O + Energy ethanol ethanal acetic acid [O] [O] [O]

Ethers

Ethers An ether: Contains an -O- between two carbon atoms. Is named from alkyl names of the attached groups (in alphabetical order) followed by ether. CH3─O─CH3 CH3─CH2─O─CH3 dimethyl ether ethyl methyl ether

Cyclic Ethers One of the atoms in a ring is oxygen.

Physical Properties of Ethers They are polar compounds (because of C-O). Weak dipole-dipole interactions. Low boiling points: Hydrocarbons < ethers < alcohols. More soluble in water than other hydrocarbons of similar molecular weight (H-bond with water). δ- δ+ C-O (3.5 – 2.5 = 1) H δ+ O H δ-

Chemical Properties of Ethers Ethers are resistant to chemical reactions (inert). Oxidation Reduction Good solvent for organic reactions.

Thiols

Thiols An Thiol: Contains an –SH (sulfhydryl) group. Is named by selecting the longest carbon chain that contain the -SH. We add -thiol to the name of the parent alkane. Parent chain is numbered from the end nearest to the -SH group. CH3─S─H CH3─CH2─S─H Methanethiol Ethanethiol

Naming Thiols Step 1 Step 2 Step 3 Step 4 Select the longest carbon chain that contains the -SH group. Step 2 Number from the end nearest -SH group. Step 3 Add –thiol to the name of the parent alkane. Use the number to show the location of -SH. Step 4 Give the location and name of each substituent (alphabetical order) as a prefix to the name of the main chain.

4-Methyl-1-pentanethiol CH3 CH3CHCH2CH2CH2SH 4-Methyl-1-pentanethiol 5 4 3 2 1 CH3 CH3CHCH2SH 2-Methyl-1-propanethiol 3 2 1 Cl CH3 SH CH3-CH-CH2-CH-CH-CH3 5-Chloro-3-methyl-2-hexanethiol 6 5 4 3 2 1

Physical Properties of Thiols They have unpleasant odors. They are nonpolar compounds. S-H (2.5 – 2.1 = 0.4) nonpolar covalent. 3. Low boiling points (London dispersion forces). 4. Almost insoluble in water.

Chemical Properties of Thiols 1. Thiols are weak acids (react with strong bases). H2O CH3CH2SH + NaOH CH3CH2S-Na+ + H2O Sodium ethanethiolate 2. Oxidation to disulfides: -S-S- disulfide Oxidation 2HOCH3CH2SH + O2 HOCH2CH2S-SCH2CH2OH Reduction

Chirality

same connectivity Stereoisomers Chiral Enantiomers Diastereomers Constitutional Isomers Cis-Trans Isomers with stereocenters without Achiral different

A

superposable mirror images Achiral superposable mirror images 2-propanol This means that the original and its mirror image are the similar molecules.

nonsuperposable mirror images Enantiomers (chiral) nonsuperposable mirror images 2-butanol They have different chemical and physical properties.

stereocenter A carbon with four different groups bonded to it. It usually creates enantiomers.