Note that propane and ethanol have nearly the same molar mass, but their melting points differ by 120 degrees C.Butane and propanol also have nearly the same molar mass, and their boiling points vary by almost 97 degrees C.This is dramatic experimental evidence of the effect of polarity and hydrogen bonding on the strength of intermolecular forces.
The term “miscible” means that two substances will form a mixture in any proportion. So, for instance, 50 mL of water plus 50 mL of ethanol will form a mixture. But 1 mL of ethanol will mix with 99 mL of water just as well as 1 mL of water will mix with 99 mL of ethanol.Solubility is the maximum amount of a solute that can be dissolved in a given amount of solvent. In this case, solubility is expressed in units of moles solute per 100 grams water.
Note that the ratio of carbons to hydroxyl groups is 2:1 for the 1,4-butanediol, the same as the ratio for ethanol. And both ethanol and 1,4-butanediol are completely miscible with water.
4-methyl-3-hexanol is the reactant.The two products are 2-hexene and 3-hexene. 3-hexene is more highly substituted and is the major product.
The reactant is 2-methyl-2-propanol.There is only one product because the molecule is symmetric around the carbon attached to the hydroxyl group.The product is 2-methyl-1-propene.
The reactant is 2-methylcyclohexanol.The two products are 1-methylcyclohexene and 3-methylcyclohexene.Since 1-methylcyclohexene has the more highly substituted double bond, it is the major product.
Oxidation requires that a second oxygen-carbon bond be formed to the carbinol carbon. In the case of primary and secondary alcohols, there is a hydrogen also attached to the carbinol carbon, and its loss allows the carbinol carbon to form another bond to oxygen. [Remember, carbon can only form four bonds!] For a tertiary alcohol, there are only alkyl groups attached to the carbinol carbon (no hydrogens) in addition to the hydroxyl group. The only way another carbon-oxygen bond could form would be if one of the alkyl groups left the carbinol carbon. And this would no longer be an oxidation reaction, because the ending product(s) would be different from the initial alcohol in other ways besides just having one more oxygen-carbon bond.
Preparation of acetone:Hydration: Add water across the double bond. According to Markovnikov’s rule, the OH will be on carbon 2.Oxidation: Adding an oxidizing agent to the alcohol makes it into a ketone (C-O changed to C=O).
Chapter 12Alcohols, Phenols, Thiols, and Ethers 1
1. Alcohols: structure and propertiesThe functional group found on all alcohols is the hydroxylgroup, -OH.Alcohols are like water molecules, but with an alkyl group(-R) substituted for one of the hydrogens. H-OH R-OH 2
1. Alcohols: structure and propertiesSince oxygen is moreelectronegative than carbonand hydrogen, the hydroxylgroup makes alcohol moleculespolar.This polarity, along with thehydrogen bonded to oxygen,allows alcohols to hydrogen-bond. 3
1. Alcohols: structure and propertiesThe strength of hydrogen-bonding causes alcohols tohave higher melting and boiling points than thecorresponding hydrocarbons. Compound Molar Mass Boiling Point CH3CH2CH3 44 g/mol -42 oC CH3CH2OH 46 g/mol +78.5 oC CH3CH2CH2CH3 58 g/mol -0.5 oC CH3CH2CH2OH 60 g/mol 97.2 oC 5
1. Alcohols: structure and propertiesSmall alcohol molecules (1-4 carbons) are very soluble inwater.Alcohols with 5-6 carbons are moderately soluble inwater.Larger alcohols are not appreciably soluble in water. WHY? 6
1. Alcohols: structure and propertiesName Formula Water solubility*methanol CH3OH miscibleethanol C2H5OH misciblepropanol C3H7OH misciblebutanol C4H9OH 0.11pentanol C5H11OH 0.030hexanol C6H13OH 0.0058heptanol C7H15OH 0.0008 *mol/100g at 25oC 7
1. Alcohols: structure and propertiesThe hydroxyl end of an alcohol molecule is hydrophilic. “Water-loving”The nonpolar hydrocarbon portion of the alcoholmolecule is hydrophobic. “Water-fearing”As the nonpolar portion becomes larger relative to thepolar portion, water solubility decreases. 8
1. Alcohols: structure and properties The presence of multiple hydroxyl groups on a carbon chain will increase solubility.Name Formula Water solubility*butanol 0.111,4-butanediol miscible Tegrity lecture video 9
1. Alcohols: structure and properties Here’s Journal question number one!tag = alcohols What characteristic of alcohols is responsible for both their high boiling points and their high degree of solubility in water? How does this characteristic cause high boiling points and high solubilities? 11
2. Alcohols: Nomenclature1) Name the parent compound based on the longest carbon chain or the carbon ring.2) Replace the parent name ending –e with –ol.3) Number the parent chain to give the hydroxyl carbon the lowest possible number.4) Identify, name, and number all additional substituents. 12
2. Alcohols: Nomenclature1) Name the parent compound based on the longest carbon chain or the carbon ring. butane2) Replace the parent name ending –e with –ol. butanol3) Number the parent chain to give the hydroxyl carbon the lowest possible number. 2-butanol4) Identify, name, and number all additional substituents. 3-methyl-2-butanol 13
2. Alcohols: NomenclatureName the following compounds: pencast 14
2. Alcohols: NomenclatureDraw structures for the following compounds: 2-methyl-1-propanol 2-chlorocyclopentanol pencast 2,4-dimethylcyclohexanol 2,3-dichloro-3-hexanol 1,2,3-pentanetriol 15
4. Classification of alcoholsIn an alcohol, the carbon atom with the hydroxyl group (-OH) attached to it is called the .What distinguishes the four carbinol carbons above? 16
4. Classification of alcoholsMethanol is in a class by itself, with 0 carbons/3hydrogens attached to the carbinol carbon.Primary (1o) alcohols have 1 carbon/2 hydrogensattached to the carbinol carbon. ethanolSecondary (2o) alcohols have 2 carbons/1 hydrogenattached to the carbinol carbon. 2-propanolTertiary (3o) alcohols have 3 carbons/0 hydrogensattached to the carbinol carbon. 2-methyl-2-propanol 17
4. Classification of alcoholsMethanol(1o)(2o)(3o) 18
4. Classification of alcohols Alcohols often react differently depending on their classification as 1o, 2o, or 3o. A fourth classification is aromatic alcohol, with the hydroxyl group attached to a carbon on an aromatic ring. The simplest of these is phenol.Tegrity lecture video 19
4. Classification of alcoholsName each alcohol and classify it as 1o, 2o, or 3o. pencast 20
5. Reactions involving alcoholsPreparation of alcohols: hydration of an alkene See slides 39-42 of the Chapter 11 powerpoint. Remember that Markovnikov’s rule applies. 21
5. Reactions involving alcoholsPreparation of alcohols: hydrogenation of aldehydesand ketones. Addition of H2 to a double bond (C=O) These reactions are also called reductions (fewer C-O bonds, more C-H bonds) catalyst catalyst 22
5. Reactions involving alcoholsWrite a balanced equation for the hydrogenation ofethanal (two-carbon aldehyde).Name the product. pencast 23
5. Reactions involving alcoholsWrite a balanced equation for the hydrogenation of 2-hexanone (six-carbon ketone). pencastName the product. 24
5. Reactions involving alcoholsDehydration of alcohols Dehydration is the reverse of hydration. Dehydration is a type of elimination reaction. In the presence of heat and a strong acid, -OH and –H are removed from adjacent carbon atoms. A double bond is formed between these atoms. 25
5. Reactions involving alcoholsSometimes, more than one product of dehydration ispossible. major product minor product 2-butanol 2-butene 1-buteneZaitsev’s rule: In an elimination reaction, the morehighly substituted product alkene will be the majorproduct. 26
5. Reactions involving alcoholsGive the product(s) of dehydration of the followingalcohol. Name the reactant and the product(s). pencast 27
5. Reactions involving alcoholsGive the product(s) of dehydration of the followingalcohol. Name the reactant and the product(s). pencast 28
5. Reactions involving alcoholsGive the product(s) ofdehydration of thisalcohol. Name thereactant and theproduct(s). pencast 29
5. Reactions involving alcoholsOxidation reactions in organic chemistry Oxidation is a gain of a bond to oxygen and loss of a bond to hydrogen. Reduction is the flip side of oxidation—loss of a bond to oxygen and gain of a bond to hydrogen.An oxidizing agent causes oxidation to take place and isitself reduced. basic potassium permanganate (KMnO4/OH-) chromic acid (H2CrO4) general symbol [O] over the reaction arrow 30
5. Reactions involving alcohols Oxidation reactions in organic chemistryTegrity lecture video 31
5. Reactions involving alcohols Here’s Journal question #2.Tag = oxidation Combustion of an alkane to produce carbon dioxide (and water) is an oxidation reaction. Now that you know oxidation involves forming more bonds to oxygen and fewer bonds to hydrogen, give the [hypothetical] steps in the combustion (that is, oxidation) of methane to carbon dioxide. Each step should produce a molecule with one more carbon-oxygen bond and one less carbon-hydrogen bond. Name the molecule produced in each step, ending with carbon dioxide. There are four steps and four product molecules if you include carbon dioxide. 32
5. Reactions involving alcohols Tegrity lecture video 34
5. Reactions involving alcoholsDraw the product of oxidation of the following alcoholsand name the product. propanol pencast cyclohexanol 2-methyl-2-hexanol 1-methyl-1-cyclopentanol 3-phenyl-1-propanol pencastHow can acetone be prepared from propene? 35
5. Reactions involving alcoholsWhen ethanol is metabolized in the liver in the followingseries of reactions, catalyzed by liver enzymes.What causes a hangover? Step 2 of oxidation 36
6. Oxidation and reduction in living systemsIn inorganic reactions, oxidation and reduction are oftenaccompanied by changes in charge and transfer ofelectrons. Oxidation of sodium: Na Na+ + e- Reduction of chlorine: Cl + e- Cl-In organic systems, there are normally no changes incharge or obvious transfers of electrons. Oxidation: more bonds to oxygen or fewer bonds to hydrogen Reduction: fewer bonds to oxygen or more bonds to hydrogen 37
6. Oxidation and reduction in living systems more oxidized formalkane alcohol aldehyde carboxylic acid more reduced form 38
7. PhenolsCompounds with a hydroxyl group attached to a benzenering are called phenols.As with alcohols, the hydroxyl group makes thecompound polar and can participate in hydrogenbonding.Smaller phenols are slightly soluble in water. 39
7. PhenolsThe compound phenol is a solid at room temperatures; is colorless and poisonous; has a penetrating odor; turns red when exposed to air.The acid-base indicatorphenolphthalein has two phenolic hydroxyl groups; is colorless in acidic solution; is deep magenta in basic solution. 40
8. EthersEthers are similar to alcohols, but the –H of the hydroxylgroup is replaced by another –R group. alcohol etherIntermolecular forces are weaker in ethers than inalcohols because the absence of an O-H bond precludeshydrogen bonding.Ethers are slightly polar due to the C-O bonds. 41
8. EthersBoiling points of ethers are higher than for the corresponding alkanes. much lower than for the corresponding alcohols. Tegrity lecture video 42
8. Naming ethersThe IUPAC names for ethers are based on the alkanename of the longest chain attached to the oxygen.The shorter chain is named as an alkoxy substituent, analkane with the -ane replaced by –oxy. CH3CH2CH2CH2CH2-O-CH3 1-methoxypentaneGive the IUPAC names for the ethers on the next slide. 43
8. Naming ethersGive the IUPAC names for the following ethers. pencast 44
8. Synthesis of ethersA dehydration (removal of water) reaction between twoalcohols will produce an ether.Heat and the presence of hydrogen ions are necessary forthe reaction to take place. ethanol + ethanol ethoxyethane + water 45
8. Synthesis of ethersIf two different alcohols undergo a dehydration, amixture of products is possible. methoxyethane ethanol + methanol methoxymethane ethoxyethane 46
8. Synthesis of ethers And finally, Journal question #3.Tag = solubility Compare the relative solubilities in water of alkanes, alcohols, phenols, and ethers. Explain their relative solubilities in terms of their differing molecular structures and their intermolecular forces with water molecules. 47
9. ThiolsThe sulfhydryl group, -SH, is analogousto the hydroxyl group, -OH.A compound with a sulfhydryl group iscalled a thiol.Thiols are named by adding the suffixthiol to the name of the parentcompound. 48
9. ThiolsName the following compounds: pencast 49
9. ThiolsDraw structures for the following compounds: 1,3-butanedithiol 2-methyl-2-pentanethiol pencast 2-chloro-2-propanethiol cyclopentanethiol 50
9. ThiolsTwo thiols can be oxidized (lose hydrogen) to form adisulfide. + 2 H+ + 2 e-Disulfide bonds are important for the structure andshape of many proteins. (more about this in Module 8) 51