Chapter 14 Alcohols, Ethers, and Thiols Alcohols, Ethers, and Thiols

Alcohols Alcohol:OH(hydroxyl) groupAlcohol: an -OH (hydroxyl) group bonded to a tetrahedral carbon Nomenclature 1.longest chain with the -OH group numbered lowest possible (rings OH=1) eol 2.change the ending of the parent alkane from - e to -ol 3.name and number substituents and list them in alphabetical order

Nomenclature

Nomenclature Problem:Problem: write the IUPAC name for each alcohol

Nomenclature Solution:Solution:

Nomenclature diol triol –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 on –IUPAC names for diols, triols, and so on retain the final "-e" in the name of the parent alkane glycols –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

Physical Properties –bp increases as MW increases –solubility in water decreases as MW increases

Acidity of Alcohols Alcohols have about the same pK a values as water; aqueous solutions of alcohols have the same pH as that of pure water phenols contain an OH group that is more acidic –phenols are weak acids and react with NaOH and other strong bases to form water-soluble salts

Dehydration Dehydration:Dehydration: elimination of a molecule of water from adjacent carbon atoms gives an alkene –heating an alcohol with either 85% H 3 PO 4 or concentrated H 2 SO 4 –1° alcohols are the most difficult to dehydrate –2° alcohols undergo reaction at lower temperatures –3° alcohols easily undergo acid-catalyzed dehydration at temperatures only slightly above room temperature

Dehydration

Your Lab Work BP = 160 o C BP = 89 o C

Dehydration –when isomeric alkenes can be obtained, the alkene having the greater number of alkyl groups on the double bond predominates –examples:

Dehydration-Hydration competing reactions –the following equilibrium exists –in accordance with Le Chatelier's principle, excess water favor alcohol formation, whereas removal of water from the equilibrium mixture favors alkene formation

Addition or Elimination Here A is acting negative and Q is acting positive. If you can remove A or Q from the reaction what happens? If you can remove the alkene from the reaction what happens? If you can precipitate the product from this reaction what happens?

Eliminations This reaction is run is a solvent which the product salt is insoluble. How would you make the chlorocyclohexane from the cyclohexane?

3 More electrophylic Additions

Oxidation Oxidation of a 1° alcohol gives an aldehyde or a carboxylic acid –1° alcohol to acid is carried out using K 2 Cr 2 O 7 in aqueous sulfuric acid –it may be possible to stop the oxidation at the aldehyde stage by distilling the mixture; the aldehyde usually has a lower boiling point than either the 1° alcohol or the carboxylic acid

Oxidation –oxidation of a 2° alcohol gives a ketone –tertiary alcohols are resistant to oxidation

Ethers etherThe functional group of an ether is an oxygen atom bonded to two carbon atoms –the simplest ether is dimethyl ether –the most common ether is diethyl ether

Nomenclature Although ethers can be named according to the IUPAC system, chemists almost invariably use common names for low-molecular-weight ethers –common names are derived by listing the alkyl groups bonded to oxygen in alphabetical order and adding the word "ether” –alternatively, name one of the groups on oxygen as an alkoxy group

Nomenclature Cyclic ether:Cyclic ether: an ether in which one of the atoms in a ring is oxygen –cyclic ethers are also known by their common names –ethylene oxide is an important building block for the organic chemical industry; it is also used as a fumigant in foodstuffs and textiles, and in hospitals to sterilize surgical instruments –tetrahydrofuran is a useful laboratory and industrial solvent

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

Making an Ether Williamson Ether Synthesis

Symmetrical Ethers

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 H 2 in the presence of a transition metal catalyst –they are not affected by most acids or bases at moderate temperatures (but can eliminate) 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

Thiols Thiol:SH(sulfhydryl) groupThiol: a compound containing an -SH (sulfhydryl) group –the most noteworthy physical property of low-molecular- weight thiols is their stench –they are responsible for scents such as those from rotten eggs and sewage –Skunk scent is due to a molecule which has two thiols

Thiols - Nomenclature IUPAC names are derived in the same manner as are the names of alcohols -e -thiol –to show that the compound is a thiol, the final -e of the parent alkane is retained and the suffix -thiol added mercaptanCommon names for simple thiols are derived by naming the alkyl group bonded to -SH and adding the word "mercaptan"

Physical Properties Because of the small difference in electronegativity between sulfur and hydrogen ( = 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

Reactions of Thiols Thiols are weak acids (pK a 10), and are comparable in strength to phenols –thiols react with strong bases such as NaOH to form water-soluble thiolate salts

Reactions of Thiols disulfide(-S-S-) bondThe most common reaction of thiols in biological systems is their oxidation to disulfides, the functional group of which is a disulfide (-S-S-) bond –thiols are readily oxidized to disulfides by O 2 –they are so susceptible to oxidation that they must be protected from contact with air during storage –disulfides, in turn, are easily reduced to thiols by several reducing agents.

Important Alcohols

Acid Base Equilibrium and

Basic conditions What? Substitution or Elimination –Leaving group must be weak base. –Attaching group is stronger base which is negatively charged or neutral with lone pair electrons.

Acidic Conditions What? Substitution or Elimination –Acid activates the leaving group so that it is a weak base. –Attaching group is a neutral lone pair atom.

End Chapter 14 Alcohols, Ethers, and Thiols

Review Alkanes – Reactions of only –Combustion –Radical Halogenation

Review Aromatic – Reactions of only –Substitution (Electrophilic Aromatic Substitution)

Review Alkenes – Reactions of –Electrophilic Addition

Review Alkenes – Synthesis –Elimination Basic Acidic

Review Alkynes –Just do everything twice 2 eliminations Or Two additons

Review Alcohols –Synthesis

Review Alcohols –Reactions of

Review Thiols –Synthesis

Review Thiols –Reactions

Review Alkylhalides –Synthesis

Review Alkylhalides –Reactions of