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Chapter 5 Alcohols Thiols Ethers. Chapter 102 Structure of Water and Methanol Oxygen is sp 3 hybridized and tetrahedral. The H—O—H angle in water is 104.5°.

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Presentation on theme: "Chapter 5 Alcohols Thiols Ethers. Chapter 102 Structure of Water and Methanol Oxygen is sp 3 hybridized and tetrahedral. The H—O—H angle in water is 104.5°."— Presentation transcript:

1 Chapter 5 Alcohols Thiols Ethers

2 Chapter 102 Structure of Water and Methanol Oxygen is sp 3 hybridized and tetrahedral. The H—O—H angle in water is 104.5°. The C—O—H angle in methyl alcohol is 108.9°.

3 Chapter 103 Classification of Alcohols Primary: carbon with —OH is bonded to one other carbon. Secondary: carbon with —OH is bonded to two other carbons. Tertiary: carbon with —OH is bonded to three other carbons. Aromatic (phenol): —OH is bonded to a benzene ring.

4 Chapter 104 Examples of Classifications CH 3 C CH 3 CH 3 OH * CH 3 CH OH CH 2 CH 3 * CH 3 CH CH 3 CH 2 OH *

5 Chapter 105 Examples of Classifications CH 3 C CH 3 CH 3 OH * CH 3 CH OH CH 2 CH 3 * CH 3 CH CH 3 CH 2 OH * Primary alcohol

6 Chapter 106 Examples of Classifications CH 3 C CH 3 CH 3 OH * CH 3 CH OH CH 2 CH 3 * CH 3 CH CH 3 CH 2 OH * Primary alcoholSecondary alcohol

7 Chapter 107 Examples of Classifications CH 3 C CH 3 CH 3 OH * CH 3 CH OH CH 2 CH 3 * CH 3 CH CH 3 CH 2 OH * Primary alcoholSecondary alcohol Tertiary alcohol

8 Chapter 108 IUPAC Nomenclature Find the longest carbon chain containing the carbon with the —OH group. Drop the -e from the alkane name, add -ol. Number the chain giving the —OH group the lowest number possible. Number and name all substituents and write them in alphabetical order.

9 Chapter 109 Examples of Nomenclature 2-methyl-1-propanol 2-methylpropan-1-ol 2-methyl-2-propanol 2-methylpropan-2-ol 2-butanol butan-2-ol CH 3 C CH 3 CH 3 OH CH 3 CH CH 3 CH 2 OH CH 3 CH OH CH 2 CH

10 Chapter 1010 Alkenols (Enols) Hydroxyl group takes precedence. Assign the carbon with the —OH the lowest number. End the name in –ol, but also specify that there is a double bond by using the ending –ene before -ol 4-penten-2-ol pent-4-ene-2-ol CH 2 CHCH 2 CHCH 3 OH

11 Chapter 1011 Naming Priority 1.Acids 2.Esters 3.Aldehydes 4.Ketones 5.Alcohols 6.Amines 7.Alkenes 8.Alkynes 9.Alkanes 10. Ethers 11. Halides Highest ranking Lowest ranking

12 Chapter 1012 Hydroxy Substituent When —OH is part of a higher priority class of compound, it is named as hydroxy. 4-hydroxybutanoic acid also known as  -hydroxybutyric acid (GHB) CH 2 CH 2 CH 2 COOH OH carboxylic acid

13 Chapter 1013 Common Names Alcohol can be named as alkyl alcohol. Useful only for small alkyl groups. isobutyl alcohol sec-butyl alcohol CH 3 CH CH 3 CH 2 OH CH 3 CH OH CH 2 CH 3

14 Chapter 1014 Naming Diols Two numbers are needed to locate the two —OH groups. Use -diol as suffix instead of -ol. hexane-1,6- diol

15 Chapter 1015 Glycols 1, 2-diols (vicinal diols) are called glycols. Common names for glycols use the name of the alkene from which they were made. ethane-1,2- diol ethylene glycol propane-1,2- diol propylene glycol

16 Chapter 1016 Phenol Nomenclature —OH group is assumed to be on carbon 1. For common names of disubstituted phenols, use ortho- for 1,2; meta- for 1,3; and para- for 1,4. Methyl phenols are cresols. 3-chlorophenol (meta-chlorophenol) 4-methylphenol (para-cresol)

17 Chapter 1017 Give the systematic (IUPAC) name for the following alcohol. The longest chain contains six carbon atoms, but it does not contain the carbon bonded to the hydroxyl group. The longest chain containing the carbon bonded to the —OH group is the one outlined by the green box, containing five carbon atoms. This chain is numbered from right to left in order to give the hydroxyl-bearing carbon atom the lowest possible number. The correct name for this compound is 3-(iodomethyl)-2-isopropylpentan-1-ol. Solved Problem 1 Solution

18 Chapter 1018 Physical Properties Alcohols have high boiling points due to hydrogen bonding between molecules. Small alcohols are miscible in water, but solubility decreases as the size of the alkyl group increases.

19 Chapter 1019 Boiling Points of alcohols Alcohols have higher boiling points than ethers and alkanes because alcohols can form hydrogen bonds. The stronger interaction between alcohol molecules will require more energy to break them resulting in a higher boiling point.

20 Chapter 1020 Solubility in Water Small alcohols are miscible in water, but solubility decreases as the size of the alkyl group increases.

21 Chapter 1021 Methanol “Wood alcohol” Industrial production from synthesis gas Common industrial solvent Toxic Dose: 100 mL methanol Used as fuel at Indianapolis 500 – Fire can be extinguished with water – High octane rating – Low emissions – Lower energy content – Invisible flame

22 Chapter 1022 Ethanol Fermentation of sugar and starches in grains 12–15% alcohol, then yeast cells die Distillation produces “hard” liquors Azeotrope: 95% ethanol, constant boiling Denatured alcohol used as solvent Gasahol: 10% ethanol in gasoline Toxic dose: 200 mL

23 Chapter 1023 Acidity of Alcohols pK a range: 15.5–18.0 (water: 15.7) Acidity decreases as the number of carbons increase. Halogens and other electron withdrawing groups increase the acidity. Phenol is 100 million times more acidic than cyclohexanol!

24 Chapter 1024 Table of K a Values

25 Chapter 1025 Formation of Alkoxide Ions Ethanol reacts with sodium metal to form sodium ethoxide (NaOCH 2 CH 3 ), a strong base commonly used for elimination reactions. More hindered alcohols like 2-propanol or tert-butanol react faster with potassium than with sodium.

26 Chapter 1026 Formation of Phenoxide Ion The aromatic alcohol phenol is more acidic than aliphatic alcohols due to the ability of aromatic rings to delocalize the negative charge of the oxygen within the carbons of the ring.

27 Chapter 1027 Charge Delocalization on the Phenoxide Ion The negative charge of the oxygen can be delocalized over four atoms of the phenoxide ion. There are three other resonance structures that can localize the charge in three different carbons of the ring. The true structure is a hybrid between the four resonance forms.

28 Chapter 1028 Synthesis of Alcohols (Review) Alcohols can be synthesized by nucleophilic substitution of alkyl halide. Hydration of alkenes also produce alcohols:

29 Chapter 1029 Synthesis of Vicinal Diols Vicinal diols can be synthesized by two different methods: Syn hydroxylation of alkenes – Cold, dilute, basic potassium permanganate

30 Chapter 1030 Reduction of Carbonyl Reduction of aldehyde yields 1º alcohol. Reduction of ketone yields 2º alcohol. Reagents: – Sodium borohydride, NaBH 4 – Lithium aluminum hydride, LiAlH 4 – Raney nickel

31 Chapter 1031 Sodium Borohydride NaBH 4 is a source of hydrides (H - ) Hydride attacks the carbonyl carbon, forming an alkoxide ion. Then the alkoxide ion is protonated by dilute acid. Only reacts with carbonyl of aldehyde or ketone, not with carbonyls of esters or carboxylic acids.

32 Chapter 1032 Lithium Aluminum Hydride LiAlH 4 is source of hydrides (H - ) Stronger reducing agent than sodium borohydride, but dangerous to work with. Reduces ketones and aldehydes into the corresponding alcohol. Converts esters and carboxylic acids to 1º alcohols.

33 Chapter 1033 Reduction with LiAlH 4 The LiAlH 4 (or LAH) will add two hydrides to the ester to form the primary alkyl halide. The mechanism is similar to the attack of Grignards on esters.

34 Chapter 1034 Reducing Agents NaBH 4 can reduce aldehydes and ketones but not esters and carboxylic acids. LiAlH 4 is a stronger reducing agent and will reduce all carbonyls.

35 Chapter 1035 Catalytic Hydrogenation Raney nickel is a hydrogen rich nickel powder that is more reactive than Pd or Pt catalysts. This reaction is not commonly used because it will also reduce double and triple bonds that may be present in the molecule. Hydride reagents are more selective so they are used more frequently for carbonyl reductions.

36 Chapter 1036 Thiols (Mercaptans) Sulfur analogues of alcohols are called thiols. The —SH group is called a mercapto group. Named by adding the suffix -thiol to the alkane name. They are commonly made by a substitution. Primary alkyl halides work better.

37 Chapter 1037 Synthesis of Thiols The thiolate will attack the carbon displacing the halide. This is a substitution reaction methyl halides will react faster than primary alkyl halides. To prevent dialylation use a large excess of sodium hydrosulfide with the alkyl halide.

38 Chapter 1138 Alcohol Reactions Dehydration to alkene Oxidation to aldehyde, ketone Substitution to form alkyl halide Reduction to alkane Esterification Williamson synthesis of ether

39 Chapter 1139 Summary Table

40 Chapter 1140 Oxidation States Easy for inorganic salts (reduced, organic oxidized) – CrO 4 2- reduced to Cr 2 O 3 – KMnO 4 reduced to MnO 2 Oxidation: loss of H 2, gain of O, O 2, or X 2 Reduction: gain of H 2 or H -, loss of O, O 2, or X 2 Neither: gain or loss of H +, H 2 O, HX

41 Chapter 1141 Oxidation States Easy for inorganic salts (reduced, organic oxidized) – CrO 4 2- reduced to Cr 2 O 3 – KMnO 4 reduced to MnO 2 Oxidation: loss of H 2, gain of O, O 2, or X 2 Reduction: gain of H 2 or H -, loss of O, O 2, or X 2 Neither: gain or loss of H +, H 2 O, HX

42 Chapter º, 2º, 3º Carbons

43 Chapter 1143 Oxidation of 2° Alcohols 2° alcohol becomes a ketone Reagent is Na 2 Cr 2 O 7 /H 2 SO 4 = H 2 CrO 4 Active reagent probably H 2 CrO 4 Color change: orange to greenish-blue =>

44 Chapter 1144 Oxidation of 1° Alcohols 1° alcohol to aldehyde to carboxylic acid Difficult to stop at aldehyde Use pyridinium chlorochromate (PCC) to limit the oxidation. PCC can also be used to oxidize 2° alcohols to ketones.

45 Chapter ° Alcohols Don’t Oxidize Cannot lose 2 H’s Basis for chromic acid test

46 Chapter 1146 Alcohol as a Nucleophile ROH is weak nucleophile RO - is strong nucleophile New O-C bond forms, O-H bond breaks.

47 Chapter 1147 Alcohol as an Electrophile OH - is not a good leaving group unless it is protonated, but most nucleophiles are strong bases which would remove H +. Convert to tosylate (good leaving group) to react with strong nucleophile (base).  + + C-Nuc bond forms, C-O bond breaks

48 Chapter 1148 Reduction of Alcohols Dehydrate with conc. H 2 SO 4, then add H 2

49 Chapter 1149 Reaction with HBr -OH of alcohol is protonated -OH 2 + is good leaving group 3° and 2° alcohols react with Br - via S N 1 1° alcohols react via S N 2

50 Chapter 1150 Reaction with HCl Chloride is a weaker nucleophile than bromide. Add ZnCl 2, which bonds strongly with -OH, to promote the reaction. The chloride product is insoluble. Lucas test: ZnCl 2 in conc. HCl – 1° alcohols react slowly or not at all. – 2  alcohols react in 1-5 minutes. – 3  alcohols react in less than 1 minute.

51 Chapter 1151 Limitations of HX Reactions Poor yields of 1° and 2° chlorides May get alkene instead of alkyl halide

52 Chapter 1152 Reactions with Phosphorus Halides Good yields with 1° and 2° alcohols PCl 3 for alkyl chloride (but SOCl 2 better) PBr 3 for alkyl bromide

53 Chapter 1153 Dehydration Reactions Conc. H 2 SO 4 (or H 3 PO 4 ) produces alkene Carbocation intermediate Zaitsev product Bimolecular dehydration produces ether Low temp, 140°C and below, favors ether High temp, 180°C and above, favors alkene

54 Ethers O H H O H R O R R Hydrogen Oxide Aka Water AlcoholEther Ethers contain an sp 3 hybridized oxygen atom Ethers do not hydrogen bond between each other, but will hydrogen bond with water and alcohols. Ethers are polar and water soluble

55 Ether Nomenclature Common System Give alkyl names to the carbon groups (alkyl groups) bonded to the oxygen, followed by ether. Examples

56 Ether Nomenclature Common System Give alkyl names to the carbon groups (alkyl groups) bonded to the oxygen, followed by ether. Examples Dimethyl ether

57 Ether Nomenclature Common System Give alkyl names to the carbon groups (alkyl groups) bonded to the oxygen, followed by ether. Examples Dimethyl ether Ethylmethyl ether

58 Ether Nomenclature Common System Give alkyl names to the carbon groups (alkyl groups) bonded to the oxygen, followed by ether. Examples Dimethyl ether Ethylmethyl ether Isopropylmethyl ether

59 Ether Nomenclature Common System Give alkyl names to the carbon groups (alkyl groups) bonded to the oxygen, followed by ether. Examples Dimethyl ether Ethylmethyl ether Isopropylmethyl ether Sec-butylcyclopropyl ether

60 Ether Nomenclature IUPAC System Name the longest chain of carbons in the normal fashion. The oxygen containing group is named by giving the carbon portion the Latin root followed by oxy. Examples Methoxymethane

61 Ether Nomenclature IUPAC System Name the longest chain of carbons in the normal fashion. The oxygen containing group is named by giving the carbon portion the Latin root followed by oxy. Examples Methoxymethane Methoxyethane

62 Ether Nomenclature IUPAC System Name the longest chain of carbons in the normal fashion. The oxygen containing group is named by giving the carbon portion the Latin root followed by oxy. Examples Methoxymethane Methoxyethane 2-Methoxypropane

63 Ether Nomenclature IUPAC System Name the longest chain of carbons in the normal fashion. The oxygen containing group is named by giving the carbon portion the Latin root followed by oxy. Examples Methoxymethane Methoxyethane 2-Methoxypropane 2-Cyclopropoxybutane

64 Ether Formation Primary alcohols can dehydrate to ethers This reaction occurs at lower temperature than the competing dehydration to an alkene This method generally does not work with secondary or tertiary alcohols because elimination competes strongly The mechanism is an S N 2 reaction:

65 Williamson Ether Synthesis Good for unsymmetrical ethers

66 Chapter 1166 Dehydration Mechanisms

67 Chapter 1167 Esterification Fischer: alcohol + carboxylic acid Nitrate esters Phosphate esters

68 Chapter 1168 Fischer Esterification Acid + Alcohol yields Ester + Water Sulfuric acid is a catalyst. Each step is reversible.

69 Chapter 1169 Sulfate Esters Alcohol + Sulfuric Acid =>

70 Chapter 1170 Nitrate Esters

71 Chapter 1171 Phosphate Esters =>

72 Chapter 1172 Phosphate Esters in DNA =>

73 Chapter 1173 End of Chapter 5


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