University:
Eastern Kentucky University
Course:
CHE 361 | Organic Chemistry I
Academic year:

2020
Views:

24

Pages:

1
Author:

Alma Hester

Organic Chemistry 9: Carboxylic Acid Derivative Amides, Esters, and Anhydrides Reactivity Principles Amides: The condensation product of carboxylic acid and ammonia or an amine. Amides are given the suffix –amide. The alkyl groups on a substituted amide are written at the beginning of the name with the prefix N-. Cyclic amides are called lactams, named with the Greek letter of the carbon forming the bond with the N. N,N-Dimethylpropanamide b-Lactam Esters: The condensation products of carboxylic acids with alcohols, i.e., a Fischer Esterification. Esters are given the suffix –oate. The esterifying group is written as a substituent, without a number. Cyclic esters are called lactones, named by the number of carbons in the ring and the Greek letter of the carbon forming the bond with the oxygen. Triacylglycerols include three ester bonds between glycerol and fatty acids. Isopropyl butanoate b-Propiolactone Anhydrides: The condensation dimers of carboxylic acids. Symmetric anhydrides are named for the parent carb acid, followed by anhydride. Asymmetric anhydrides are named by listing the parent carb acids alphabetically, followed by anhydride. Some cyclic anhydrides can be synthesized by heating dioic acids. Five- or six-membered rings are generally stable. Ethanoic propanoic anhydride Ethanoic anhydride Succinic anhydride Fischer Esterification In Nu- substitution reactions, reactivity is: acid chloride > anhydrides > esters > amides > carboxylate Steric Hindrance: Describes when a reaction cannot proceed (or significantly slows) because substituents crowd the reactive site. Protecting groups, such as acetals, can be used to increase steric hindrance or otherwise decrease the reactivity of a particular portion of a molecule Induction: Refers to uneven distribution of charge across a s bond because of differences in EN. The more EN groups in a carbonyl-containing compound, the greater its reactivity Conjugation: Refers to the presence of alternating single and multiple bonds, which creates delocalized p electron clouds above and below the plane of the molecule. Electrons experience resonance through the unhybridized p-orbitals, increasing stability. Conjugated carbonyl-containing compounds are more reactive because they can stabilize their transition states. Conjugation in Benzene Ring Strain: Increased strain in a molecule can make it more reactive. b-lactams are prone to hydrolysis because they have significant ring strain. Ring strain is due to torsional strain from eclipsing interactions and angle strain from compression bond angles below 109.5° Nucleophilic Acyl Substitution Reactions All carboxylic acid derivatives can undergo nucleophilic substitution reactions. The rates at which they do so is determined by their relative reactivities. Cleavage: Anhydrides can be cleaved by the addition of a nucleophile. Addition of ammonia or an amine results in an amide and a carboxylic acid. Addition of an alcohol results in an ester and a carboxylic acid. Addition of water results in two carboxylic acids. Synthesis of an Anhydride via Carboxylic Acid Condensation Transesterification: The exchange of one esterifying group for another on an ester. The attacking nucleophile is an alcohol. Amides: Can be hydrolyzed to carboxylic acids under strongly acidic or basic conditions. The attacking nucleophile is water or the hydroxide anion.