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Chemistry 203 Review Organic Chemistry Bonding Goal of atoms Filled valence level 1. Ionic bonds 2. Covalent bonds Noble gases (Stable) Bonding Ionic bonds result from the transfer of electrons from one element to another. Cation (Y+) Metals: lose 1, 2 or 3 e- Ions Nonmetals: gain 1, 2 or 3 e- Anion (X-) Cation (Y+): Na+ Li+ Ca2+ Anion (X-): Cl- F- O2- Al3+ Bonding Ionic bonds Metal-Nonmetal Cl: 1s2 2s2 2p6 3s2 3p5 Na: 1s2 2s2 2p6 3s1 Na+: - Cl : 1s2 2s2 2p6 3s2 3p6 1s2 2s2 2p6 Ne Cation Ar Anion Bonding Covalent bonds result from the sharing of electrons between two atoms. Nonmetal-Nonmetal Metalloid-Nonmetal Sharing of valence electrons Lewis Dot Structure H Li He Al C N Cl Lewis Structure H H Or H H Cl Or Cl H H Cl: 1s2 2s2 2p6 3s2 3p5 H: 1s1 Ar: 1s2 2s2 2p6 3s2 3p6 He: 1s2 Intermolecular Forces London dispersion forces Intermolecular Forces Dipole-dipole interaction < Ionic bonds Covalent bonds Intramolecular (Bonding) Forces Hydrogen bonding London dispersion forces Attractive forces between all molecules Only forces between nonpolar covalent molecules _ He He 2+ _ 2+ _ _ He δ- _ _ δ+ 2+ Original Temporary Dipole No Polarity He δ- _ _ δ+ 2+ Original Temporary Dipole He δ- _ _ δ+ 2+ Induced Temporary Dipole He + _ 2+ _ London dispersion forces He: T↓ Kinetic energy ↓ Move slower T = -240°C (1 atm) → liquid Attractive forces become more important liquid Dipole-Dipole Interactions Attractive forces between two polar molecules stronger than London dispersion forces boiling point ↑ Hydrogen bonding Between H bonded to O, N, or F (high electronegativity) → δ+ and a nearby O, N, or F → δhydrogen bond H - + O H H O H H 2O (a) Stronger than dipole-dipole interactions & London dispersion forces Hydrogen bonding δ+ CH3COOH Acetic acid δ- H-bonding in our body H-bond H-bond Protein (α-helix) DNA Intermolecular Forces Solubility polar dissolves polar like dissolves like Nonpolar dissolves nonpolar octane CCl4 octane + CCl4 Organic Compounds Hydrocarbons Large family of organic compounds Composed of only carbon and hydrogen Saturated hydrocarbons Unsaturated hydrocarbons Alkanes H Alkenes, Alkynes & Aromatics H C-C C=C H C C C C C H CC C H Alkanes Chemical reactions of Alkanes Low reactivity 1- Combustion: • Alkanes react with oxygen. • CO2, H2O, and energy are produced. • Alkane + O2 CH4 + 2O2 CO2 + H2O + heat CO2 + 2H2O + energy Chemical reactions of Alkanes Low reactivity 2- Halogenation: Alkanes react with Halogens. CH4 + Cl2 CH3Cl + HCl Chloromethane CH2Cl2 + HCl Dichloromethane CHCl3 + HCl Trichloromethane CCl4 + HCl Tetrachloromethane Heat or light CH3Cl+ Cl2 Heat or light CH2Cl2+ Cl2 Heat or light CHCl3+ Cl2 Heat or light Alkenes & Alkyens Chemical properties of Alkenes & Alkynes More reactive than Alkanes Addition of Hydrogen (Hydrogenation-Reduction) Addition of Hydrogen Halides (Hydrohalogenation) Addition of water (Hydration) Addition of Bromine & Chlorine (Halogenation) Chemical properties of Alkenes & Alkynes Addition reactions –C = C – – C – C– Exothermic reactions Products are more stable (have the lower energy). Chemical properties of Alkenes & Alkynes More reactive than Alkanes 1. Hydrogenation (Reduction): • A hydrogen atom adds to each carbon atom of a double bond. • A catalyst such as platinum or palladium is used (Transition metals). H H │ │ H–C=C–H + H2 Ethene Pt Pt H H │ │ H– C – C– H │ │ H H Ethane Chemical properties of Alkenes & Alkynes More reactive than Alkanes 2. Hydrohalogenation: • A hydrogen halide (HCl, HBr, or HI) adds to alkene to give haloalkane. H H H H │ │ │ │ H–C=C–H + HCl Ethene H– C – C– H │ │ H Cl Chloroethane Chemical properties of Alkenes & Alkynes 2. Hydrohalogenation: - reaction is regioselective. - Markovnikov’s rule: H adds to double bonded carbon that has the greater number of H and halogen adds to the other carbon. CH3 CH=CH2 + HCl Prop ene Cl H CH3 CH-CH2 H Cl CH3 CH-CH2 2-Ch loroprop ane 1-Chlorop ropan e (not formed) The rich get richer! Chemical properties of Alkenes & Alkynes 3. Hydration (addition of water): • Water adds to C=C to give an alcohol. • Acid catalyst (concentrated sulfuric acid). • A regioselective reaction (Markovnikov’s rule). CH3 CH=CH2 Propene CH3 CH3 C=CH2 + + 2-Methylp ropen e H2 O H2 O H2 SO4 OH H CH3 CH-CH2 2-Propan ol CH3 H2 SO4 CH3 C-CH2 HO H 2-Methyl-2-prop anol Chemical properties of Alkenes & Alkynes More reactives than Alkanes 4. Halogenation: • A halogen atom adds to each carbon atom of a double bond. • Usually by using an inert solvent like CH2Cl2. H H │ │ CH3–C=C–CH3 + Cl2 2-Butene CH2Cl2 H H │ │ CH3– C – C– CH3 │ │ Cl Cl 2,3-dichlorobutane Aromatic Hydrocarbons Chemical properties of aromatics No addition reactions (almost unreactive) Aromatic substitution: One of the H atoms is repalecd by some groups. Halogenation Nitration Sulfonation Chemical properties of benzene 1. Halogenation: Cl and Br react rapidly with benzene in the presence of an iron catalyst. H + Cl2 Benzene FeCl3 Cl + HCl Chlorobenzene Chemical properties of benzene 2. Nitration: In presence of concentrated nitric acid and sulfuric acid, one of the H atoms is replaced by a nitro (-NO2) group. H + HNO3 H2 SO4 NO2 + H2 O Nitrob enzene Chemical properties of benzene 3. Sulfonation: In presence of concentrated sulfuric acid and heat, one of the H atoms is replaced by sufonic acid (-SO3H) group. H + H2 SO4 Heat SO3 H + H2 O Benzenes ulfon ic acid Alcohols OH OH + NaOH Phenol H2 O O- Na + + S od ium phenoxide (a w ater-soluble salt) Chemical Properties of Alcohols 1. Acidity of Alcohols: H2 O OH + NaOH Phenol O- Na+ + H2 O S od ium phenoxide (a w ater-soluble salt) 2. Acid-Catalyzed Dehydration: CH3CH2OH -C–CH OH H2SO4 180°C CH2 = CH2 + H2O Dehydration Hydration C = C + H20 3. Oxidation of Alcohols: Acid-Catalyzed Dehydration Alkene having the greater number of alkyl groups on the double bond generally predominates. OH CH3 CH2 CHCH3 2-Butanol H3 PO4 -H2 O CH3 CH=CHCH3 + CH3 CH2 CH=CH2 2-Bu tene 1-Butene (80%) (20%) CH3 CH3 CH3 H2 SO4 CH3 CHCHCH3 CH3 C=CHCH3 + CH3 CHCH=CH2 -H2 O OH 3-Meth yl-2-b utanol 2-Methyl-2-b utene 3-Methyl-1-bu tene (major prod uct) Oxidation of 1° Alcohols In the oxidation [O] of a primary alcohol 1, one H is removed from the –OH group and another H from the C bonded to the –OH. primary alcohol OH │ CH3─C─H │ H ethanol (ethyl alcohol) [O] K2Cr2O7 H2SO4 aldehyde O ║ CH3─C─H + H2O ethanal (acetaldehyde) Oxidation of 2° Alcohols The oxidation of 2 alcohols is similar to 1°, except that a ketone is formed. [O] secondary alcohol OH │ CH3─C─CH3 │ H 2-propanol K2Cr2O7 H2SO4 ketone O ║ CH3─C─CH3 + H2O 2-propanone Oxidation of 3° Alcohols Tertiary 3 alcohols cannot be oxidized. Tertiary alcohol OH │ CH3─C─CH3 [O] no reaction K2Cr2O7 H2SO4 no product │ CH3 no H on the C-OH to oxidize 2-methyl-2-propanol Thiols Chemical Properties of Thiols 1. Thiols are weak acids (react with strong bases). CH3CH2SH + NaOH H2O CH3CH2S-Na+ + H2O Sodium ethanethiolate 2. Oxidation to disulfides: -S-S- disulfide Oxidation 2HOCH3CH2SH + O2 Reduction HOCH2CH2S-SCH2CH2OH Amines NH CH22 CH3 CH3-NH2 C CH3-NH-CH3 Eth ylb enzene Tolu Chemical properties of Amines They are weak bases (like ammonia): react with acids. (to form water-soluble salts) H CH3 N.. + .. H – .. O–H H CH3 H N + H -... . ..O – H H (a) (CH3 CH2 ) 2 NH + HCl (CH3 CH2 ) 2 NH2 + ClD ieth ylammoniu m chloride CH3 COO- + CH3 COOH (b) N N+ H Pyridinium acetate Aldehydes & Ketones Chemical properties of Aldehydes and Ketones 1. Oxidation: only for aldehydes (not for ketones). O O CH3─CH2─CH2─CH2─C─H = = K2Cr2O7 CH3─CH2─CH2─CH2─C─OH H2SO4 Pentanal Pentanoic acid K2Cr2O7: Oxidizing agent Liquid aldehydes are sensetive to oxidation. O C 2 H O C + O2 2 OH No oxidizing agent Benzaldehyde Benzoic acid Chemical properties of Aldehydes and Ketones 2. Reduction: Like reducing the alkene (C = C) to alkane (C – C): – Reduction of an aldehyde gives a primary alcohol (-CH2OH). – Reduction of a ketone gives a secondary alcohol (-CHOH-). = O + H2 Pentanal 1-Pen tan ol = O CH3─C─CH2─CH3 2-butanone CH3─CH2─CH2─CH2─CH2─ OH + H 2 tran si ti o n m etal catal y st OH - CH3─CH2─CH2─CH2─C─ H tran si ti on metal cataly st CH3─CH─CH2─CH3 2-butanol Chemical properties of Aldehydes and Ketones 3. Addition of alcohols (hemiacetals): H of the alcohol adds to the carbonyl oxygen and OR adds to the carbonyl carbon. O H C + O-CH2 CH3 H Benzaldehyde Ethanol O-H C OCH2 CH3 H A hemiacetal unstable Chemical properties of Aldehydes and Ketones 3. Addition of alcohols (Acetals): O-H Acid C OCH2 CH3 + H O-CH 2 CH 3 H A hemiacetal Ethanol O CH2CH3 C OCH2 CH3 + H2O H An Acetal Chemical properties of Aldehydes and Ketones 3. Addition of alcohols (hemiacetals): If –OH is part of the same molecule that contains C=O. O 5 4 3 2 1 H O-H 4-Hyd roxypentanal redraw to show the -OH an d -CHO clos e to each oth er 3 2 1 4 5 O H C H O H O-H O A cyclic hemiacetal Carboxylic Acids carbonyl group O CH3 — C—OH hydroxyl Carboxyl group Chemical properties of Carboxylic Acids 1- Reaction with bases: COOH + NaOH H2 O Ben zoic acid (slightly soluble in water) COOH + + COO Na + H2 O Sodiu m b enzoate (60 g/100 mL water) NH3 Benzoic acid (s ligh tly solub le in w ater) H2 O - COO NH4 + Ammoniu m b enzoate (20 g/100 mL water) Chemical properties of Carboxylic Acids 2- Reduction: Resistant to reduction Using a powerful reducing agent: LiAlH4 (Lithium aluminum hydride). 1° alcohol O COH 3-cyclopentenecarboxylic acid LiAlH4, ether H2O CH2OH 4-Hydroxymethylcyclopentene Chemical properties of Carboxylic Acids 3- Fischer Esterification: - A carboxylic acid reacts with an alcohols to form an ester. - Using an acid catalyst such as concentrated sulfuric acid. O H2 SO4 CH3 C-OH + H-OCH2 CH3 Ethanoic acid Ethanol (Acetic acid) (Ethyl alcohol) O CH3 COCH2 CH3 + H2 O Ethyl ethanoate (Ethyl acetate) The best way to prepare an ester. Chemical properties of Carboxylic Acids 4- Decarboxylation: Loss of CO2 from a carboxyl group. O RCOH decarboxylation Heat RH + CO 2 Esters & Amides O CH3 — C — NH2 Amide group Formation of Esters O RCO H A carboxylic acid Fischer Esterification O RC- OH H-OR' A carboxylic acid An alcohol H2SO4 O RCOR' + H2O An ester Chemical Reactions of Esters 1. Hydrolysis: reaction with water. (breaking a bond and adding the elements of water) O RCOR' + H2O An ester Heat Acid O RC- OH A carboxylic acid + H-OR' An alcohol Chemical Reactions of Esters 2. Saponification (Hydrolysis): an ester reacts with a hot aqueous base. O RCOR' + NaOH Heat H2O An ester O CH3COCH2CH3 + NaOH Ethyl Ethanoate O + RCO-Na + A sodium salt H- OR' An alcohol O - + CH3CO-Na + CH3CH2OH Sodium acetate Ethanol Chemical Reactions of Esters 3. Esters react with ammonia and with 1° and 2° amines to form amides. O O OCH2 CH3 + N H3 Ethyl 2-phenyl acetate N H2 + CH3 CH2 OH 2-Phenylacetamide Thus, an amide can be prepared from a carboxylic acid by first converting the carboxylic acid to an ester by Fischer esterification and then reaction of the ester with an amine. Formation of Amides O RCO H A carboxylic acid O RC- OH H-NHR' A carboxylic acid An Amine O CH3 C- OH + HHNCH2 CH3 Acetic acid Ethanamine Heat O RCNHR' + H2O An amide O CH3 C- NHCH2 CH3 + H2 O N-ethylethanamide Chemical Reactions of Amides Such as esters: Hydrolysis in hot aqueous acid or base. O CH3 CH2 CH2 CNH2 + H2 O + HCl H2 O heat Butanamide O CH3 CNH Acetanilide + NaOH H2 O heat O + CH3 CH2 CH2 COH + NH4 Cl Butanoic acid O CH3 CO-Na+ + H2 N Sodium acetate Aniline Chemical Reactions of Amides Amides do not react with ammonia or with amines.