Organic Chemistry Carboxylic Acids

Question 1

___ contain a hydroxyl group (-OH) attached to a carbonyl carbon (C||O), represented by the formula -COOH. This functionality is known as a carboxyl group, which is always a terminal group on a molecule. Carboxylic acids are the most highly oxidized organic compounds (other than carbon dioxide). The carbonyl carbon of a carboxylic acid has three bonds to oxygen, two within the carbonyl C||O and the other to the oxygen of the -OH group

Answer 1

carboxylic acids

Question 2

The hydrogen atoms of the -OH group are highly acidic with pK sub a values in the general range of 3 to 6. As with other carbonyl compounds, the C||O group is polarized with a partial positive ___ on the carbon and a partial negative charge on the oxygen. Carboxylic acids occur widely in nature and are synthesized by many living organisms. There are numerous of preparing carboxylic acids, but three are of particular interest: oxidation of alcohols and alkenes, carbonation with Grignard reagents, and hydrolysis of nitriles. These three mechanisms are important to study both as synthetic pathways of carboxylic acids and also as reaction pathways of other compounds. The reactions of carboxylic acids are likewise interrelated with those of other compounds and are often driven by the dipole moment of the carbon-oxygen double bond. Carboxylic acids can be reduced to form alcohols. They can serve as the substrate for nucleophilic attack and substitution to form acyl halides, anhydrides, esters, and amides. They can decarboxylate to produce CO2, and long-chain carboxylic acids can form soaps and micelles

Answer 2

charge

Question 3

In the IUPAC system of ___ carboxylic acids are named by adding the suffix -oic acid to the alkyl root. Since carboxylic acids are highly oxidized, they have very high priority in naming, and the chain is numbered so that the carboxyl group receives the lowest possible number

Answer 3

nomenclature

Question 4

___ were among the first organic compounds discovered. Their original names continue today in the common system of nomenclature

Answer 4

carboxylic acids

Question 5

Cyclic carboxylic acids are usually named as ___. The carbon atom to which the carboxyl group is attached is numbered 1 because of the group’s high priority. When a carboxylic acid is deprotonated, its name is changed to end in the suffix -ate. Thus, acetic acid becomes acetate when ionized and is called sodium acetate when in its sodium salt form

Answer 5

cycloalkane carboxylic acids

Question 6

___ - compounds with two carboxyl groups - are common in biological systems. The first six straight-chain terminal dicarboxylic acids are oxalic malonic, succinic, glutaric, adipic, and pimelic acids. Their IUPAC names are ethanedioic acid, propanedioic acid, butanedioic acid, pentanedioic acid, hexanedioic acid, and heptanedioic acid

Answer 6

dicarboxylic acids

Question 7

Carboxylic acids are polar and form hydrogen bonds between the -OH group of one molecule and the lone pairs of electrons on the oxygen of another molecule. As a result, carboxylic acids can form dimers: pairs of molecules connected by hydrogen bonds. The boiling points of carboxylic acids are therefore even higher than those of the corresponding alcohols. The ___ follow the usual trend of increasing the molecular weight

Answer 7

boiling points

Question 8

The ___ of carboxylic acids is due to the resonance stabilization of the carboxylate anion (the conjugate base). When the hydroxyl proton dissociates from the acid, the negative charge left on the carboxylate group is delocalized an shared by both oxygen atoms

Answer 8

acidity

Question 9

___ on carbon atoms adjacent to a carboxyl group can influence acidity. Electron-withdrawing groups such as -Cl or -NO2 further delocalize the negative charge and increase acidity. Electron-donating groups such as -NH2 or -OCH3 destabilize the negative charge, making the compound less acidic.

Answer 9

substituents

Question 10

In dicarboxylic acids, one -COOH group (which is electron withdrawing) influences the other, making the first carboxyl group more acidic than the analogous monocarboxylic acid. The ___ group is then influenced by the carboxylate anion. Ionization of the second group will create a doubly charged species, in which the two negative charges repel each other. Since this is unfavorable, the second proton is less acidic than that of a monocarboxylic acid

Answer 10

second carboxyl

Question 11

beta-dicarboxylic acids are notable for the high acidity of the ___ located between the two carboxyl groups (pK sub a ~ 10). Loss of this acidic hydrogen atom produces a carbanion that is stabilized by the electron-withdrawing effect of the two carboxyl groups

Answer 11

alpha-hydrogens

Question 12

The same ___ is also seen in beta-ketoacids

Answer 12

effect

Question 13

___ can be prepared via oxidation of aldehydes, primary alcohols, and certain alkylbenzenes. Any strong oxidizing agent, including KMnO4, K2Cr2O7, and CrO3, will create a carboxylic acid. A primary alcohol can also be oxidized first with PCC to create an aldehyde and then further oxidized with Tollen’s reagent to create the carboxylic acid

Answer 13

carboxylic acids

Question 14

Carboxylic acids can also be ___ by the oxidative cleavage of alkenes

Answer 14

prepared

Question 15

___, such as Grignard reagents, react with carbon dioxide (CO2) to form carboxylic acids. This reaction is useful for the conversion of tertiary alkyl halides into carboxylic acids, which cannot be accomplished through other methods. Note that this reaction adds one carbon atom to the chain.

Answer 15

organometallic reagents

Question 16

___, also called cyanides, are compounds containing the functional group -C|||N. The cyanide atom CN- is a strong nucleophile and will displace primary and secondary halides in typical SN2 fashion. Nitriles can be hydrolyzed under either acidic or basic conditions. The products are carboxylic acids and ammonia (or ammonium salts). This allows the conversion of alkyl halides into carboxylic acids. As in the carbonation reaction, an additional carbon atom is introduced to the carbon chin. For instance, if the desired product is acetic acid, a possible starting material would by methyl iodide

Answer 16

nitriles

Question 17

Many of the reactions of ___ can be explained by a single mechanism: nucleophilic substitution. This mechanism is very similar to nucleophilic addition to a carbonyl. The key difference between the two is that nucleophilic substitution concludes with re-formation of the C||O double bond and elimination of a leaving group

Answer 17

carboxylic acids

Question 18

___ occupy the most oxidized position of the oxidation-reduction continuum. Carboxylic acids can be reduced with lithium aluminum hydride (LAH) to their corresponding primary alcohols. Note that this reaction will not occur when the milder reducing agent NaBH4 is used. Aldehyde intermediates that may be formed in the course of the reaction with LAH are also reduced to the primary alcohol. The reaction occurs by nucleophilic addition of hydride (the H- ion) to the carbonyl group and elimination of water as a leaving group

Answer 18

Carboxylic acids

Question 19

Carboxylic acids react with alcohols under acidic conditions to form ___ and water. In acidic solution, the oxygen on the carbonyl group can become protonated. This increases the polarity of the carbon-oxygen bond, putting even more positive charge on the carbon and making it even more susceptible to nucleophilic attack. Again, water is eliminated as a leaving group and the carbonyl re-forms. This condensation reaction occurs most rapidly with primary alcohols.

Answer 19

esters

Question 20

Acyl halides, also called ___, are compounds with carbonyl groups bonded to halides. Several different reagents can accomplish this transformation; thionyl chloride, SOCl2, is the most common. Acid chlorides are very reactive, as the greater electron-withdrawing power of the Cl- makes the carbonyl carbon more susceptible to nucleophilic attack than the carbonyl carbon of a carboxylic acid. Also, chlorine is an excellent leaving group, making acid chlorides highly reactive. They are frequently used as intermediates in the conversion of carboxylic acids to esters and amides.

Answer 20

acid halides

Question 21

Carboxylic acids can undergo decarboxylation reactions, resulting in the loss of ___ and thus loss of the entire carboxyl group.
1,3-dicarboxylic acids and other beta-keto acids may spontaneously decarboxylate when heated. The carboxyl group is lost and replaced with a hydrogen. the reaction proceeds through a six-membered ring transition state. The enol initially formed tautomerizes to the more stable keto form as the final product

Answer 21

carbon dioxide

Question 22

When long-chain ___ carboxylic acids react with sodium or potassium hydroxide, they form salts. These salts, called soaps, are able to solubilize nonpolar organic compounds in aqueous solutions because they possess both a nonpolar “tail” and a polar carboxylate “head.”

Answer 22

hydrocarbon

Question 23

When placed in aqueous solution, soap molecules arrange themselves into spherical structures called ___. The polar heads face outward, where they can be solvated by water molecules, and the nonpolar hydrocarbon chains re inside the sphere, protected from the solvent. Nonpolar molecules such as grease can dissolve in the hydrocarbon interior of the spherical micelle, while the micelle as a whole is soluble in water because of its polar shell

Answer 23

micelles