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SC CHEM 334 - Carboxylic acids

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Chem 334 1nd Edition Lecture 13Outline of Last Lecture I. Acetals and oxidation of aldehydesOutline of Current Lecture II. NomenclatureIII. Physical propertiesIV. Synthesis of Carboxylic acidsCurrent LectureNomenclature:Dicarboxylic acids are created when you have two carboxylic acids in the same molecule. When naming dicaroxylic acids, leave the “e” on the end of the name of the carbon chain, and instead add “dioic acid” to the end of the molecule name. O O OH OH Pentane dioic acidPhysical properties:Carboxylic acids associate through hydrogen bonds, which increases the boiling point. You can see this when you compare the boiling points molecules with similar molecular weights O O OH OH HBp: 118⁰C Bp: 97⁰C Bp: 48⁰CH2O solubility is also higher for carboxylic acids due to their hydrogen bondsSolubility:O O OH > OH > HThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.Acidity:Resonance structures makes the carboxylate more acidic than the other two structures above, as it’s possible for the molecule to share a negative charge between oxygens. Substituent and inductive effects: O O Cl O OH Cl OH Cl OHPka: 4.76 Pka: 2.86 Pka: 1.48Having more substituents on the carboxylic acid will lower pka. Similarly, inductive effects, which come from the polarization of a covalent bond by adjacent electronegative atoms, will also lower the pka. The partial positive charge of the carbon attached to the substituent will help to stabilize the negative charge.However, inductive effects drop off with distance. The longer the carbon chain is between the substituent and the C=O bond, the greater the pka. So, once the partial positive charge is so far away, it can no longer help to stabilize the negative charge.Acidity of Substituted benzoic acids: O OH Pka 4.46O O OH Pka 4.16 O OH pka 3.42O2NElectron drawing groups on the ring decreases acidity, as it puts electron density into ring which doesn’t help to stabilize the negative. On the other hand, electron withdrawing groups increase acidity by helping to stabilize the negative.Solubility of carboxylic acid depends on the environment and pH of the solution.O O OH NaOH O- Not H2O soluble H2O solubleSynthesis of Carboxylic Acids:1. Oxidation of Alkenes:A. KMnO4 OH + O O OH KMnO4 O OH O OHB. Change Ozonolysis Workup O3 O O H2O2 + OH OHP O3 O H2O2 OH x2 Ph O3 OH O H2O2 + O OH2. Oxidation of primary alcohols and aldehydesOH OR KMnO4 R OHOH OR H2CrO4 R OHOH O R H KMnO4 R OH H2CrO4OH O R H Ag2O,OH- R OH H3O3. Oxidation of Benzylic position O KMnO4 OH O KMnO4 OH OH O H2CrO4 OH4. Hydrolysis of Nitriles:Acidic conditions: R–≡N H+, H2O Δ O R OHBasic conditions: R–≡N H+, H2O Δ O H3O Workup O R O R OHAcidic Mechanism: N–H N–H H–O+–H R–≡N: H–O+–H R–≡N+–H H–O–H R O+–H R OH H H H2O HH–N–H H–N–H H–N–H H R OH H–O–H R OH R OH H–O–H H–N–H H–O+–H H2O OH H R OH HO:R OH R OH H–O H2O O O ≡N H+, H2O, Δ OH O I NaCN ≡N H3O, Δ OHBasic Mechanism: N N–H N–H H–O+–H R–≡N: HO- R OH H–O–H R OH R OH OH OH NH2 NH2 R O–H R O R OH R OH H–O–H O NH3 -OH OO–H OH O ≡N OH, H2O, Δ OH H3O, wkup OPrimary and secondary alkyl halides  Nitrile adds one carbon to carboxylic acid or aldehyde5. Carbonation of Grignards or organolithiums (adds CO2) O OR–Cl Mg R–MgCl CO2 R O- H+workup R OH Et2O Mechanism:R–MgCl O O H3O OH O R O Wkup R


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SC CHEM 334 - Carboxylic acids

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