Organic Chemistry II - Carboxylic Acids and their Derivatives - Quick Guides

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Study GuideOrganic Chemistry II–Carboxylic Acids and theirDerivatives1.Introduction to Carboxylic AcidsCarboxylic acidsare an important class of organic compounds. They all contain a special functionalgroup called thecarboxyl group, written as–COOH.This group consists of a carbonyl group (C=O) and a hydroxyl group (–OH) bonded to the samecarbon atom.Carboxylic acids and their related compounds make up a large portion of organic chemistry. Manyeveryday substances, such as vinegar and fatty acids, belong to this family.1.Common Derivatives of Carboxylic AcidsCarboxylic acids can form several closely related compounds, calledderivatives, by replacing the–OH part of the carboxyl group. The most important derivatives are:•Acid halides:–COX (where X is a halogen like Cl or Br)•Acid anhydrides:–CO–O–CO–

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Study Guide•Esters:–COOR•Amides:–CONH₂These derivatives are very common in organic reactions and are widely used in synthesis.2.Nomenclature of Carboxylic AcidsCarboxylic acids are named usingtwo systems:1.Thecommon naming system2.TheIUPAC naming system

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Study Guide3.Common NamesCommon names often come fromLatin or Greek wordsthat describe where the acid occursnaturally. For example:•Formic acidcomes fromformica(Latin for ant), because it was first isolated from ants.•Acetic acidcomes fromacetum(Latin for vinegar).•Butyric acidcomes frombutyrum(Latin for butter).These names are still widely used in chemistry and everyday language.4.IUPAC Naming of Carboxylic AcidsTo name a carboxylic acid using theIUPAC system, follow these steps:1.Find the longest carbon chainthat includes the carboxyl group.2.Take the name of the correspondingalkanewith the same number of carbon atoms.3.Remove the final “-e”from the alkane name and add“-oic acid.”

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Study Guide4.Number the carbon chain, starting from the carboxyl carbon (this carbon is always carbonnumber 1).5.Identify and name any substituents, giving their positions based on the numbering.Using these rules, a compound can be named correctly, such as2-ethyl-4-methylpentanoic acid.5.Naming Salts of Carboxylic AcidsWhen a carboxylic acid forms asalt, the name changes slightly:•Replace the“-ic acid”ending with“-ate.”•Then add the name of the metal ion.For example:•CH₃COO⁻K⁺is calledpotassium acetate(common name) orpotassium methanoate(IUPAC name).6.Acidity of Carboxylic AcidsCarboxylic acids areweak acids, but they are stronger than alcohols and phenols. TheirKa valuesare usually between10⁻⁴ and 10⁻⁵, which means they readily react with common bases like sodiumhydroxide and sodium bicarbonate.Why Are Carboxylic Acids Acidic?Their acidity comes from two main reasons:1.Resonance Effect

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Study GuideThe hydrogen in the–OH group is slightly positive because electrons are shared across thecarboxyl group. This makes it easier for the hydrogen ion (H⁺) to leave.2.Resonance Stabilization of the Conjugate BaseWhen a carboxylic acid loses a hydrogen ion, it forms acarboxylate ion.This ion is very stable because the negative charge is spread evenly over two oxygen atomsthrough resonance.7.Effect of Substituents on AcidityThe acidity of a carboxylic acid can be increased by addingelectron-withdrawing groups, such ashalogens, to the carbon chain.•These groups pull electron density away from the carboxyl group.•This makes it easier for the acid to lose a hydrogen ion.This effect isstrongest when the substituent is close to the carboxyl group(especially at theα-carbon) and becomes weaker as the substituent moves farther away.Key Takeaway•Carboxylic acids contain the–COOH functional group.•They have several important derivatives, including esters, amides, and acid halides.•Naming can be done usingcommon namesorIUPAC rules.•Carboxylic acids areweak acids, but stronger than many other organic compounds.•Their acidity is explained byresonance stabilizationandelectron-withdrawing effects.

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Study Guide2.Preparation of Carboxylic AcidsCarboxylic acids are commonly prepared byoxidation reactionsor by transforming other functionalgroups into the carboxyl group. Let’s go through the most important and commonly used methodsstep by step.1. Oxidation of AlkenesAlkenes can be converted into carboxylic acids usingstrong oxidizing agentssuch as:•Potassium permanganate (KMnO₄)•Potassium dichromate (K₂Cr₂O₇)When alkenes are heated with these oxidizing agents, thecarbon–carbon double bond breaks, andeach carbon is oxidized to form a carboxylic acid (or sometimes a ketone, depending on structure).Example:2-Pentene, when oxidized with hot KMnO₄, produces:•Ethanoic acid•Propanoic acid2. Ozonolysis of AlkenesOzonolysisis another useful method to prepare carboxylic acids indirectly.•First, ozone (O₃) reacts with an alkene to formaldehydes.•These aldehydes can then befurther oxidized easilyto carboxylic acids using mild oxidizingconditions.

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Study GuideThis method is especially useful when you want to break a double bond at a specific position.3. Oxidation of Primary Alcohols and AldehydesPrimary alcohols are easily oxidized to aldehydes, and aldehydes are further oxidized to carboxylicacids.Important points to remember:•Strong oxidizing agentssuch as KMnO₄, K₂Cr₂O₇, or chromium trioxide (CrO₃) convertprimary alcohols directly into carboxylic acids.•Aldehydes formed during the reaction do not remain stable under strong oxidation and arequickly converted into acids.Note:Mild oxidizing agents such as manganese dioxide (MnO₂) or Tollens’ reagent are only strong enoughto oxidize alcohols to aldehydes, not to acids.4. Oxidation of Alkyl BenzenesAlkyl benzenes that containbenzylic hydrogens(hydrogen atoms on the carbon next to the benzenering) can be oxidized to carboxylic acids.

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Study Guide•Strong oxidizing agents like hot KMnO₄convertany alkyl side chain(no matter how long)into a–COOH group.•The final product is alwaysbenzoic acid.Examples:•Propylbenzene → Benzoic acid•Isopropylbenzene → Benzoic acid•t-Butylbenzene does NOT reactbecause it hasno benzylic hydrogen.5. Hydrolysis of NitrilesNitriles (–C≡N) can be converted into carboxylic acids throughhydrolysis.

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Study Guide•This reaction can occur inacidic or basic conditions.•The nitrile is first converted into anamide, which is then further hydrolyzed to form acarboxylic acid.Example:•Propanenitrile → Propanoic acid•Benzonitrile → Benzoic acidKey idea:The reaction proceeds through several steps involving protonation, water attack, amide formation,and finally hydrolysis to the acid.The mechanism for these reactions involves the formation of an amide followed by hydrolysis of theamide to the acid. The mechanism follows these steps:1. The nitrogen atom of the nitrile group is protonated.

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Study Guide2. The carbocation generated in Step 1 attracts a water molecule.3. The oxonium ion loses a proton to the nitrogen atom, forming an enol.4. The enol tautomerizes to the more stable keto form.5. The amide is protonated by the acid, forming a carbocation.

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