6_Alcohols and phenols.pdf

Organic Chemistry 6: Alcohols and Phenols 1 Chapter Outline 1 Functional Groups 2 Classification of Alcohols 3 Naming Alcohols 4 Physical Properties of Alcohols 5 Chemical Properties of Alcohols 6 Common Alcohols 7 Phenols 8 Properties of Phenols 2 Classification of Alcohols 3 • Alcohol...

Organic Chemistry 6: Alcohols and Phenols 1 Chapter Outline 1 Functional Groups 2 Classification of Alcohols 3 Naming Alcohols 4 Physical Properties of Alcohols 5 Chemical Properties of Alcohols 6 Common Alcohols 7 Phenols 8 Properties of Phenols 2 Classification of Alcohols 3 • Alcohols are classified as primary (1°), secondary (2°), or tertiary (3°) depending on whether the carbon atom to which the –OH group is attached is directly bonded to one, two, or three other carbon atoms respectively. H C C C C OH C C OH C OH C C H primary (1o) secondary (2 ) alcohol alcohol H o tertiary (3o) alcohol 4 5 6 •Polyhydroxy alcohols and polyols are general terms for alcohols that have more than one –OH group per molecule. •Polyhydroxy compounds are very important molecules in living cells, as they include the carbohydrate class of biochemicals. 7 Structural Representations of Alcohols • An alcohol such as 2-butanol can be written in a single-line formula by enclosing the – OH group in parentheses and placing it after the carbon to which it is bonded. OH CH3CH2CHCH3 = CH3CH2CH(OH)CH3 8 Application to Biochemistry Blood sugar (glucose) contains five alcohol groups. Using the structure of glucose shown here, label each group as 1°, 2°, or 3°. O=CHCH(OH)CH(OH)CH(OH)CH(OH)CH2OH 9 Ethanol Menthol Cholesterol 10 Naming Alcohols 11 IUPAC Rules for Naming Alcohols 1. Select the longest continuous chain of carbon atoms containing the –OH group. 2. Number the carbon atoms in this chain so that the one bearing the -OH group has the lowest possible number. 12 IUPAC Rules for Naming Alcohols 3. Form the parent alcohol name by replacing the final –e of the corresponding alkane by –ol. When isomers are possible, locate the position of the –OH group by placing the number (hyphenated) of the carbon atom to which the –OH is bonded immediately before the parent alcohol name. 4. Name each alkyl side chain (or other group), and designate its position by number. 13 Name CH3CH2CH2CH2OH 4 3 2 1 CH3CH2CHCH2OH 1-butanol 14 Nomenclature of Alcohols OH CH3 H3C CH CH3 2-propanol (isopropyl alcohol) OH cyclohexanol H3C CH CH2CH2OH 3-methyl-1-butanol HO OH 1,3-cyclohexanediol 15 Physical Properties of Alcohols 16 Physical Properties of Alcohols • The physical properties of alcohols are related to those of both water and alkane hydrocarbons. • An alcohol molecule is made up of a water like hydroxyl group joined to a hydrocarbon like alkyl group. O H O H water R H alcohol 17 Boiling Points of Alcohols • Alcohols have relatively high boiling points. • The boiling points of the normal alcohols increase in a regular fashion with increasing number of carbon atoms. • Branched-chain alcohols have lower boiling points than corresponding straight-chain alcohols. 18 19 • Alcohols containing up to three carbon atoms are infinitely soluble in water. • The –OH group on the alcohol molecule is responsible for both the water solubility and relatively high boiling points of the low-molar-mass alcohols. 20 Hydrogen Bonding in Alcohols H O H H R O R O H O H H R H O O O H O R H R H H water-alcohol alcohol-alcohol 21 22 23 Glucose is one of the most important carbohydrates in biochemistry. It has six carbons and five alcohol groups (molar mass = 180.2 g). How would you predict the water solubility of glucose to differ from that of 1-hexanol? 24 H OH H OH OH C C C C C O H OH H H CH2OH 95 g of glucose will dissolve in 100 g of water. OH 0.6 g of 1-hexanol will dissolve in 100 g of water.25 Chemical Properties of Alcohols 26 Chemical Properties of Alcohols • • • • Acidic and Basic Properties Oxidation Dehydration Esterification 27 Basic Properties • If an alcohol is mixed with a strong acid, it will accept a proton (act as a Brønsted-Lowry base) to form a protonated alcohol or oxonium ion. H H3C O H + H2SO4 H3C - + HSO4 O H 28 Acidic Properties • • 2 H3C Alcohols can also act as BrønstedLowry acids. The resulting anion in the alcohol reaction is known as an alkoxide ion (RO-). H2 C O H + 2 Na 2 H3C H2 C Na+ O + H2 (g) sodium ethoxide 29 Oxidation 30 H R O O C OH [O] R C H + H2O aldehyde H o primary (1 ) [O] R C OH carboxylic acid alcohol R R O C OH [O] R C R ketone H o secondary (2 ) alcohol The –OH group gives an organic compound the capability of forming an aldehyde, ketone, or carboxylic acid. R R C OH [O] No reaction R o tertiary (3 ) alcohol 31 Common Oxidizing Agents • KMnO4 • K2Cr2O7 • O2 32 Dehydration • Alcohols can be dehydrated with sulfuric acid to form alkenes. H H H C C H OH 96% H2SO4 H H heat H H C C H + H2O 33 Dehydration • For many alcohols, there is more than one way to remove water. Therefore the double bond can be located in different positions. • The major product in such cases is the alkene in which the C=C bond has the greatest number of alkyl substituents on it (or the least number of hydrogens). H H3C H H C C 96% H2SO4 CH2 H3C heat H OH H 2-butanol C H C CH3 + H3C 2-butene (major product) H2 C H C CH2 + H2O 1-butene 34 Phenols 35 Phenols • The term phenol is used for the class of compounds that have a hydroxy group attached to an aromatic ring. OH 36 Naming Phenols • Many phenols are named as derivatives of the parent compound, via the general methods for naming aromatic compounds. OH OH OH Br phenol m-bromophenol NH2 p-aminophenol 37 Common Phenols OH OH OH HO HO resorcinol catechol (m-dihydroxybenzene) (o-dihydroxybenzene) OH hyrdroquinone (p-dihydroxybenzene) 38 Properties of Phenols 39 Properties of Phenols • Colorless, crystalline solid, mp = 41 °C • Highly poisonous • More acidic than alcohols and water - O Na+ OH + NaOH phenol ROH + NaOH alcohol + H2O sodium phenoxide no reaction 40 Quiz 41 42