Alcohols , enols and phenols

1. Alcohols, enols and phenols

2. Classification • Alcohols and alkyl halides are classified asprimary secondary tertiaryaccording to their "degree of substitution." • Degree of substitution is determined by countingthe number of carbon atoms directly attached tothe carbon that bears the halogen or hydroxyl group.

3. CH3 CH3CHCH2CH2CH3 CH3CCH2CH2CH3 Br OH Classification H CH3CH2CH2CH2CH2F OH primary alkyl halide secondary alcohol secondary alkyl halide tertiary alcohol

4. IUPAC Nomenclatureof Alcohols

5. CH3 CH3CCH2CH2CH3 OH CH3CHCH2CH2CH2CH3 OH Functional Class Nomenclature of Alcohols • Name the alkyl group and add "alcohol" as aseparate word. CH3CH2OH

6. CH3 CH3CCH2CH2CH3 OH CH3CHCH2CH2CH2CH3 OH Functional Class Nomenclature of Alcohols • Name the alkyl group and add "alcohol" as aseparate word. CH3CH2OH Ethyl alcohol 1,1-Dimethylbutylalcohol 1-Methylpentyl alcohol

7. CH3 CH3CCH2CH2CH3 OH CH3CHCH2CH2CH2CH3 OH Substitutive Nomenclature of Alcohols • Name as "alkanols." Replace -e ending of alkanename by -ol. • Number chain in direction that gives lowest numberto the carbon that bears the —OH group. CH3CH2OH

8. CH3 CH3CCH2CH2CH3 OH CH3CHCH2CH2CH2CH3 OH Substitutive Nomenclature of Alcohols • Name as "alkanols." Replace -e ending of alkanename by -ol. • Number chain in direction that gives lowest numberto the carbon that bears the —OH group. CH3CH2OH Ethanol 2-Methyl-2-pentanol 2-Hexanol

9. OH CH3 CH3 OH Substitutive Nomenclature of Alcohols • Hydroxyl groups outrank alkyl groups when it comes to numberingthe chain. • Number the chain in thedirection that gives the lowest number to thecarbon that bears theOH group

10. OH CH3 CH3 OH Substitutive Nomenclature of Alcohols 6-Methyl-3-heptanol 5-Methyl-2-heptanol

11. Dipole Moments • alcohols and alkyl halides are polar  = 1.9 D  = 1.7 D

12. Effect of Structure on Boiling Point • 46 • +78 • 1.7 CH3CH2OH Highest boiling point;strongest intermolecularattractive forces. Hydrogen bonding isstronger than other dipole-dipole attractions. Molecularweight Boilingpoint, °C Dipolemoment, D

13. Hydrogen bonding in ethanol

14. O O R'CCl R'COR Reaction of Alcohols with Acyl Chlorides • high yields • not reversible when carried outin presence of pyridine + + ROH HCl

15. O O R'COH R'COR Esterification • a condensation reaction • called Fischer esterification • acid catalyzed • reversible H+ + + ROH H2O

16. O O O O R'COCR' R'COR R'COH Reaction of Alcohols with Acid Anhydrides • analogous to reaction with acyl chlorides + + ROH

17. + (HO)3P O Esters of Inorganic Acids ROH + HOEWG ROEWG + H2O EWG is an electron-withdrawing group – HONO2 (HO)2SO2

18. O O O OH RCHR' Oxidation of Alcohols Primary alcohols RCH2OH RCH RCOH Secondary alcohols from H2O RCR'

19. + NAD (a coenzyme) + H O NAD CH3CH H Enzyme-catalyzed + CH3CH2OH alcohol dehydrogenase + +

20. HIO4 C C C O O HO OH Cleavage of Vicinal Diols by Periodic Acid + C

21. Enols and Enolates

22. OH O CH3CH H2C CH OH O CH3CCH3 H2C CCH3 Enol-oxo tautomerism K = 3 x 10-7 K = 6 x 10-9

23. •• O •• R2C CR' H •• O H •• R2C CR' Mechanism of Enolization(In general)

24. OH O R2CHCR' R2C CR' Enol Content • percent enol is usually very small • keto form usually 45-60 kJ/mol more stablethan enol keto enol

25. Phenols

26. OH CH3 Cl Nomenclature • named on basis of phenol as parent • substituents listed in alphabetical order • lowest numerical sequence: first point ofdifference rule 5-Chloro-2-methylphenol

27. OH OH OH OH OH OH Nomenclature 1,2-Benzenediol 1,3-Benzenediol 1,4-Benzenediol (common name:pyrocatechol) (common name:resorcinol) (common name:hydroquinone)

28. OH CO2H Nomenclature • name on basis of benzoic acid as parent • higher oxidation states of carbon outrankhydroxyl group p-Hydroxybenzoic acid

29. Structure of Phenol • phenol is planar • C—O bond distance is 136 pm, which isslightly shorter than that of CH3OH (142 pm)

30. Physical Properties The OH group of phenols allows hydrogen bondingto other phenol molecules and to water.

31. O O H Hydrogen Bonding in Phenols

32. Acidity of Phenols • most characteristic property of phenols is their acidity

33. – •• •• O O H •• •• •• Ka = 10-10 + H Ka = 10-16 – •• •• + CH3CH2O CH3CH2O H H •• •• •• Compare + +

34. OH OH OH NO2 NO2 O2N NO2 NO2 NO2 Effect of strong electron-withdrawing groupsis cumulative Ka: 7 x 10-8 1 x 10-4 4 x 10-1

35. Example: Thymol OH CH3 CH(CH3)2 Thymol(major constituent of oil of thyme)

36. Example: 2,5-Dichlorophenol OH Cl Cl 2,5-Dichlorophenol(from defensive secretion ofa species of grasshopper)

37. O OH OC(CH2)6CH3 O + CH3(CH2)6CCl O-Acylation • in the absence of AlCl3, acylation of the hydroxyl group occurs (O-acylation) (95%)

38. SN2 + + NaX ONa OR RX Typical Preparation is by Williamson Synthesis

39. acetone + CH3I OCH3 ONa heat (95%) Example

40. OH O Na2Cr2O7, H2SO4 H2O OH O Quinones • The most common examples of phenol oxidationsare the oxidations of 1,2- and 1,4-benzenediolsto give quinones. (76-81%)

41. OH OH CH3 CH3 Quinones • The most common examples of phenol oxidationsare the oxidations of 1,2- and 1,4-benzenediolsto give quinones. O O Ag2O diethyl ether (68%)

42. O OH OH O Some quinones are dyes Alizarin(red pigment)

43. O CH3 CH3O CH3O n O Some quinones are important biomolecules Ubiquinone (Coenzyme Q) n = 6-10 involved in biological electron transport

44. O CH3 CH3 CH3 CH3 CH3 CH3 O Some quinones are important biomolecules Vitamin K (blood-clotting factor)