Structures, Names and Physical Properties of Alcohol
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The document discusses the structure, nomenclature, and physical properties of alcohols. It describes the structure of alcohols as similar to water, with an sp3 hybridized oxygen atom bonded to a nonbonding pair of electrons and hydrogen or alkyl groups. Alcohols can be named using common or IUPAC nomenclature. Their physical properties include higher boiling points than alkanes due to hydrogen bonding, and solubility in water governed by hydroxyl group interactions. Characteristic reactions include acid-catalyzed dehydration to alkenes, and oxidation of primary and secondary alcohols to carbonyl compounds.
![• The acid-dissociation constant, Ka, of an alcohol is defined
by the equilibrium
R-OH + H2O R-O- + H3O+
[H3O+][RO-]
[ROH] pKa = - log (K3)
• The more smaller the pKa value, the alcohol is more acidic
Ka
Ka =](https://image.slidesharecdn.com/group2-210626063530/85/Structures-Names-and-Physical-Properties-of-Alcohol-43-320.jpg)
![REACTIVE C-H BONDS
• ([O] = Oxidizer)](https://image.slidesharecdn.com/group2-210626063530/85/Structures-Names-and-Physical-Properties-of-Alcohol-59-320.jpg)
Structures, Names and Physical Properties of Alcohol
- 1. STRUCTURES, NAMES & PHYSICAL PROPERTIES OF ALCOHOL • Structure of Alcohol • Nomenclature • Physical Properties
- 3. WHAT DO WE KNOW ABOUT ALCOHOLS? • An organic compound with a functional group (-OH) (hydroxyl group) • Has 3 classifications: primary(1°), secondary(2°) and tertiary(3°) • Saturated Alcohols – single bonds (alkane) • Unsaturated Alcohols – double/triple bonds (alkene/alkyne)
- 4. • We also know alcohols are found in disinfectant spray or in some beverages • To truly understand the STRUCTURE of an Alcohol, let’s take a look at water structure (H2O), then if we replace (1) one hydrogen with alkyl group, then we have an alcohol.
- 5. But why is it bent structure? That is because of the concept behind Shells, Subshells and Orbitals.
- 7. Key points: • Electrons move around the nucleus in “a cloud” not orbits. • Orbital – the region with a high probability of containing electrons. • Shell (energy level) – Subshells – Orbitals Example: 2nd Shell has (2) Subshells (SP) and 4 Orbitals (1 S orbital & 3 P orbitals) (2s, 2px , 2py, 2pz) • These electron clouds repel each other, they are like magnets with same charge. (closer together = more potential energy, far away with each other = less potential energy)
- 8. ORBITAL HYBRIDISATION & VSEPR THEORY
- 9. Example: H2O To get the hybridization, we will just count the atoms to bond and lone pairs Solution: 2 atom 2 lone pairs__ 4 orbitals ( s, p, p, p ) So it is sp3 hybridized (109.5° tetrahedral) / VSEPR (bent) Example: CH3OH Solution: 4 atoms 0 lone pairs__ 4 orbitals ( s, p, p, p ) sp3 hybridized (109.5° tetrahedral) / VSEPR (tetrahedral)
- 10. Example: C2H4 Solution: 3 atoms 0 lone pairs__ 3 orbitals ( s, p, p, p ) sp2 hybridized (120° planar triangular) / VSEPR (trigonal planar) Example: C2H2 Solution: 2 atoms 0 lone pairs__ 2 orbitals ( s, p, p, p ) sp hybridized (180° linear) / VSEPR (linear)
- 11. Summarize : • Structure of an alcohol is similar to water, having sp3 hybridized tetrahedral oxygen atom with nonbonding pairs of electrons occupying two of the sp3 hybrid orbitals.
- 12. NOMENCLATURE
- 13. NOMENCLATURE Common Name and (IUPAC) naming system Common Name • the name we use in our regular life (e.g. isopropyl & ethyl alcohol) • There are also unusual common names based on the person who discover, shapes, places etc. (e.g. megaphone, moronic acid, traumatic acid)
- 14. Common name: Prefix “n-” (normal) n-pentane n-pentanol Prefix “iso” isopentane isopentyl alcohol Prefix “neo” neopentane neopentyl alcohol
- 15. Common name: Prefix “sec” or ”s” sec-butanol (functional group bonded to secondary carbon) Prefix “tert” or ”t” tert-butanol (functional group bonded to tertiary carbon)
- 16. IUPAC system • The name for an alcohol uses the “-ol” suffix with the name of the parent alkane, together with a number to give the location of the hydroxyl group. 3 Steps 1. Name the longest carbon chain that contains the –OH group then drop the “- e” (alkane name) and add “-ol” 2. Number the longest carbon chain nearest to –OH group and use appropriate number to indicate the position of –OH group. 3. Name the substituents
- 21. PHYSICAL PROPERTIES • Alcohols are polar compounds • Both the C – O and O – H bonds are polar covalent • Alcohols associate in the liquid state by hydrogen bonding. • Hydrogen Bonding the attractive force between a partial positive charge on hydrogen and partial negative charge on a nearby oxygen, nitrogen, or fluorine atom. • The strength of hydrogen bonding in alcohols is approximately 2 to 5 kcal/mol.
- 22. PHYSICAL PROPERTIES Boiling Point • Alcohols have higher boiling points and are more soluble in water than hydrocarbons. • Alcohol have higher boiling points than alkanes of similar molecular weight. Alcohol boiling points increase as carbon-chain length increases. Structural Formula Name Molecular Weight (g/mol) Boiling Point (C°) Solubility in Water CH3OH CH3CH3 Methanol Ethane 32 30 65 -89 Infinite Insoluble CH3CH2OH CH3CH2CH3 Ethanol Propane 46 44 78 -42 Infinite Insoluble CH3CH2CH2OH CH3CH2CH2CH3 1-propanol Butane 60 58 97 0 Infinite Insoluble CH3CH2CH2CH2CH2OH HOCH2CH2CH2CH2OH CH2CH2CH2CH2CH2CH3 1-pentanol 1,4-butanediol Hexane 88 90 86 138 230 69 2.3g/100g Infinite Insoluble
- 23. PHYSICAL PROPERTIES Solubility • The solubility of alcohol in water is governed by the hydroxyl group present. • The hydroxyl group in alcohol is involved in the formation of intermolecular hydrogen bonding. Thus, the hydrogen bonds are formed between water and alcohol molecules which make alcohol soluble in water. • However, the alkyl group attached to the hydroxyl group is hydrophobic in nature. Thus, the solubility of alcohol decreases with the increase in the size of the alkyl group.
- 24. PHYSICAL PROPERTIES Acidity • Alcohols react with active metals such as sodium, potassium etc. to form the corresponding alkoxide. These reactions of alcohols indicate their acidic in nature. • The acidic nature of alcohol is due to the polarity of –OH bond. • The acidity of alcohols decreases when the electron-donating group is attached to the hydroxyl group as it increases the electron density on the oxygen atom. • Thus, primary alcohols are generally more acidic than secondary and tertiary alcohols.
- 25. CHARACTERISTIC REACTIONS OF ALCOHOLS • Acidity of Alcohols • Acid – Catalyzed Dehydration of Alcohols • Oxidation of Primary and Secondary Alcohols
- 27. REACTIONS OF ALCOHOLS 1. Reaction with Metals to form Salt • Alcohols react with Li, Na, K to liberate hydrogen and metal oxides.
- 28. REACTIONS OF ALCOHOLS 2. Formation of alkyl halides • Alcohols react with HBr or HI to produce alkyl bromides or alkyl halides.
- 29. REACTIONS OF ALCOHOLS 2. (A) Action of halogen acids on alcohol (Formation of alkyl halides) • Alcohols react with HBr or HI to produce alkyl bromides or alkyl halides.
- 30. REACTIONS OF ALCOHOLS 2. (B) Action of Phosphorus halides on alcohol (Formation of alkyl halides) • Alcohols react with phosphorus halides to produce alkyl halides.
- 31. REACTIONS OF ALCOHOLS 2. (C) Action of thionyl chloride on alcohol (Formation of alkyl halides) • Alcohols react with thionyl chloride in the presence of pyridine to produce alkyl halides.
- 32. REACTIONS OF ALCOHOLS 3. Formation of Ester • Alcohols react with carboxylic acid in the presence of strong acid to form esters.
- 33. REACTIONS OF ALCOHOLS 4. Formation of Carboxylic Acid Oxidation of primary alcohols and aldehydes: Primary alcohols and aldehydes on oxidation with sodium or potassium dichromate and sulphuric acid, or potassium permanganate, give the corresponding carboxylic acids.
- 34. REACTIONS OF ALCOHOLS 5. Dehydration of Alcohol • When alcohol is heated in the presence of sulfuric acid to form alkene by elimination of water.
- 35. REACTIONS OF ALCOHOLS 5. (A) E1 Dehydration of Alcohol • When alcohol is heated in the presence of sulfuric acid to form alkene by elimination of water.
- 36. REACTIONS OF ALCOHOLS 5. (B) E2 Dehydration of Alcohol • When alcohol is heated in the presence of sulfuric acid to form alkene by elimination of water.
- 37. REACTIONS OF ALCOHOLS 6. Oxidation of Alcohol • Alkyl halide undergo reduction with nascent hydrogen in presence of reducing agent like Zn/HCl to form alkanes.
- 38. REACTIONS OF ALCOHOLS 7. Catalytic Dehydrogenation of Alcohol • Alkyl halide undergo reduction with nascent hydrogen in presence of reducing agent like Zn/HCl to form alkanes.
- 39. REACTIONS OF ALCOHOLS 8. Reaction with Grignard Reagents (Formation of Alkanes) • Alkyl react with Grignard reagents(R-Mg-X) to form alkanes.
- 40. REACTIONS OF ALCOHOLS 9. Reduction of alcohol to form alkane • Alcohol undergo reduction with concentrated hydriodic acid and phosphorus to form alkanes.
- 42. • Alcohol weakly acidic. • In aqueous solution, alcohol will donated its proton to water molecule to give an alkoxide ion (R-O-). • R-OH + H2O R-O- + H3O+ Ka = ~10-16 to 10- 18 Example CH3CH2-OH + H2O CH3CH2-O- + H3O+
- 43. • The acid-dissociation constant, Ka, of an alcohol is defined by the equilibrium R-OH + H2O R-O- + H3O+ [H3O+][RO-] [ROH] pKa = - log (K3) • The more smaller the pKa value, the alcohol is more acidic Ka Ka =
- 44. • Alcohol is weakly acidic. • In aqueous solution, alcohol will donated its proton to water molecule to give an alkoxide ion (R-O-).
- 45. Compound Structural Formula pKa Hydrogen Chloride HCl -7 Acetic Acid CH3COOH 4.8 Methanol CH3OH 15.5 Water H2O 15.7 Ethanol CH3CH2OH 15.9 2-Propanol (CH3)2CHOH 17 2-Methyl-2-propanol (CH3)3COH 18 STRONGER ACID WEAKER ACID *Also given for comparison are pKa values for water, acetic acid, and hydrogen chloride.
- 46. H2O Water CH3OH Methanol CH3CH2OH Ethanol CH3CH2(OH)CH3 2-Propanol pKa = 15.7 pKa = 15.5 pKa = 15.9 pKa = 17 • Acidity depends primarily on the degree of stabilization and solvation of the alkoxide ion.
- 47. • The negatively charged oxygens of methanol and ethanol are about as accessible as hydroxide ion for solvation; these alcohols are about as acidic as water. • As the bulk of the alkyl group increases, the ability of water to solvate the alkoxide decreases, the acidity of the alcohol decreases, and the basicity of the alkoxide ion increases. • The Alkoxide ion (RO-) -the negative charge is confined to the oxygen and is not spread over the alkyl group. -this makes the RO- ion less stable and more susceptible to attack by positive ions such as H+ ions.
- 48. EFFECTS OF ACIDITY • The acidity decreases as the substitution on the alkyl group increase. -Ethyl group is an electron-donating group strengthens the –O-H bond harder to release a proton. i.e.: Methanol is more acidic than t-butyl alcohol
- 49. The present of electrons-withdrawing atoms enhances the acidity of alcohols. • The electron withdrawing atom helps to stabilized the alkoxide ion. • i.e.: 2-chloroethanol is more acidic than ethanol because the electron- withdrawing chlorine atom helps to stabilize the 2-chloroethoxide ion. • Alcohol with more than one electron withdrawing atoms are more acidic. i.e. 2,2,-dichloroethanol is more acidic than 2-chloroethanol. • Example of electron-withdrawing atom/groups: • Halogens atoms and NO2.
- 51. ACID-CATALYZED DEHYDRATION OF ALCOHOLS • We can convert an alcohol to an alkene by eliminating a molecule of water from adjacent carbon atoms in a reaction called dehydration. • Dehydration of alcohols is most often brought by heating with either 85% phosphoric acid or concentrated sulfuric acid. • Primary alcohols – the most difficult to dehydrate – generally require heating in concentrated sulfuric acid at temperatures as high as 180°C
- 52. ACID-CATALYZED DEHYDRATION OF ALCOHOLS • Secondary alcohols undergo acid-catalyzed dehydration at somewhat lower temperatures. • Tertiary alcohols generally undergo acid-catalyzed dehydration at temperatures only slightly above room temperature.
- 53. 1° Alcohols, 2° Alcohols, 3° Alcohols • When the acid-catalyzed dehydration of an alcohol yields isomeric alkenes, the alkene having the greater number of alkyl groups on the double bond generally predominates. • Hydration-dehydration reactions are reversible. Ease of Dehydration Alcohols
- 54. • Alkene hydration and alcohol dehydration are competing reactions, and the following equilibrium exists:
- 55. In accordance with Le Chatelier’s principle: • Large amounts of water (using dilute aqueous acid) favor alcohol formation. • Scarcity of water (using concentrated acid) or experimental conditions where water is removed (heating the reaction mixture above 100°C) favor alkene formation.
- 56. OXIDATION OF PRIMARY AND SECONDARY ALCOHOLS
- 57. ALCOHOL OXIDATION • Alcohol oxidation is an important organic reaction. The indirect oxidation of primary alcohols to carboxylic acids normally proceeds via the corresponding aldehyde, which is transformed via an aldehyde hydrate by reaction with water. • Primary alcohols can be oxidized to form aldehydes and carboxylic acids • Secondary alcohols can be oxidized to give ketones • Tertiary alcohols, in contrast, cannot be oxidized without breaking the molecule's C–C bonds.
- 58. OXIDATION REACTIONS • The oxidation, the orange dichromate ion is reduced to the green Cr3+ ion. This can be used to detect alcohols.
- 59. REACTIVE C-H BONDS • ([O] = Oxidizer)
- 60. REAGENTS FOR ALCOHOL OXIDATION FOR THE OXIDATION OF PRIMARY ALCOHOLS TO ALDEHYDES • Cr2O7 2– (dichromate) • CrO3/pyridine (Collins reagent) • Pyridinium chlorochromate (PCC) • Pyridinium dichromate (PDC, Cornforth reagent) • Dess–Martin periodinane • Dimethyl sulfoxide (DMSO)/oxalyl chloride (Swern oxidation)
- 61. REAGENTS FOR ALCOHOL OXIDATION FOR THE OXIDATION OF SECONDARY ALCOHOLS TO KETONES • Cr2O7 2– (dichromate) • CrO3/pyridine (Collins reagent) • Pyridinium chlorochromate (PCC) • Pyridinium dichromate (PDC, Cornforth reagent) • Dess–Martin periodinane • Dimethyl sulfoxide (DMSO)/oxalyl chloride (Swern oxidation) • Dimethyl sulfoxide (DMSO)/oxalyl chloride (Swern oxidation) • CrO3/H2SO4/acetone (Jones oxidation) • Aluminium isopropoxide/acetone (Oppenauer oxidation)
- 62. REAGENTS FOR ALCOHOL OXIDATION FOR THE DIRECT OXIDATION OF PRIMARY ALCOHOLS TO CARBOXYLIC ACIDS • KMnO4 (potassium permanganate) • RuO4 (ruthenium tetroxide) • CrO3/H2SO4/acetone (Jones oxidation)
- 63. GROUP II MEMBERS Mr. Jhonel D. Balmas (Leader)(Structure of Alcohol & Nomenclature) Ms. Mariz Bien (Physical Properties of Alcohols) Ms. Argelyn Bongalbal (Reactions of Alcohols) Ms. Roce Shelle Castillo (Acidity of Alcohols) Ms. Maybel Mata (Dehydration of Alcohol) Ms. Cenia Romo (Alcohol Oxidation)