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

2020
Views:

199

Pages:

1
Author:

grosikesf4

Organic Chemistry 6: Aldehydes and Ketones I: Electrophilicity and Oxidation-Reductio Description and Properties Nucleophilic Addition Reactions Aldehydes: Are terminal functional groups containing a carbonyl bonded to at least one hydrogen. Nomenclature: suffix –al. In rings, they are indicated by the suffix –carbaldehyde. Ketones: Internal functional groups containing a carbonyl bonded to two alkyl chains. In nomenclature, they use the suffix –one and the prefix oxo- or keto-. Carbonyl: A carbon-oxygen double bond. The reactivity of a carbonyl is dictated by the polarity of the double bond. The carbon has a d+ so it is electrophilic. Carbonyl containing compounds have a "BP than equivalent alkanes due to dipole interactions. Alcohols have "BP than carbonyls due to hydrogen bonding. Oxidation: Aldehydes and ketones are commonly produced by oxidation of primary and secondary alcohols, respectively. Weaker, anhydrous oxidizing agents like pyridinium chlorochromate (PCC) must be used for synthesizing aldehydes, or the reaction will continue oxidizing to a carboxylic acid. 1° Alcohol When a nucleophile attacks and forms a bond with a carbonyl carbon, electrons in the p bond are pushed to the oxygen atom. If there is no good leaving group (aldehydes and ketones), the carbonyl will remain open and is protonated to form an alcohol. If there is a good leaving group (carboxylic acid and derivatives), the carbonyl will reform and kick off the leaving group. Hydration Rxns: Water adds to a carbonyl, forming a geminal diol. Aldehyde or Ketone Gem-diol Aldehyde + Alcohol: When one equivalent of alcohol reacts with an aldehyde, a hemiacetal is formed. When the same rxn occurs with a ketone, a hemiketal is formed. When another equivalent of alcohol reacts with a hemiacetal (via nucleophilic substitution), an acetal is formed. When the same reaction occurs with a hemiketal, a ketal is formed. Aldehyde Oxidation-Reduction Reactions Aldehydes: Aldehydes can be oxidized to carboxylic acids using an oxidizing agent like KMnO4, CrO3, Ag2O, or H2O2. They can be reduced to primary alcohols via hydride reagents (LiAlH4, NaBH4). Ketones: Ketones cannot be further oxidized, but can be reduced to secondary alcohols using the same hydride reagents. Nitrogen + Carbonyl: Nitrogen and nitrogen derivatives react with carbonyls to form imines, oximes, hydrazones, and semicarbazones. Imines can tautomerize to form enamines. Common Oxidizing / Reducing Agents Oxidizing Agent PCC Reactant Product 1° alcohol Aldehyde 1° Amine KMnO4 or H2Cr2O4 Aldehyde or Ketone Imine Ketone 2° alcohol 1° alcohol Carboxylic Acid Reducing Agent 2° alcohol Ketone Reactant Product Imine NaBH4 Aldehydes / Ketones 1° alcohol 2° alcohol Enamine HCN + Carbonyl: Hydrogen cyanide reacts with carbonyls to form cyanohydrins. LiAlH4 (LAH) Aldehydes Carboxylic Acid Ketones 1° alcohol 2° alcohol Ester 1° alcohol 2° alcohol 18