Organic Chemistry Lecture Outline Carbonyl-Containing Functional Groups

FUNCTIONAL GROUPS CONTAINING CARBONYL GROUPS A carbonyl group has a carbon atom doubly bonded to an oxygen atom. 1. The carbon atom of a carbonyl group is sp2 hybridized. 2. A carbonyl group is polarized with the oxygen atom bearing a partial negative and the carbon bearing a partial positive charge. 3. The carbon atom of a carbonyl group is electrophilic.

The following functional groups contain a carbonyl group. ALDEHYDES AMIDES KETONES ESTERS IMIDES ACID CHLORIDES ANHYDRIDES CARBOXYLIC ACIDS

GENERAL TYPES OF REACTIONS CARBONYL GROUPS UNDERGO 1. NUCLEOPHILIC ADDITION REACTIONS: Occurs with all types of carbonyls 2. NUCLEOPHILIC ACYL SUBSTITUTIONS: Occurs with acids, acid chlorides,amides, esters, anhydrides, imides 3. ALPHA-SUBSTITUTION REACTIONS: Occurs with all carbonyls that bear an alpha hydrogen atom 4. CARBONYL CONDENSATION REACTIONS: Occurs between two carbonyl groups

ALDEHYDES AND KETONES Aldehydes and ketones are carbonyl-containing functional groups. The structures and reactivity of these functional groups are similar. Aldehydes have a hydrogen atom and a carbon atom bonded to the carbonyl carbon. Ketones have two carbon atoms bonded to the carbonyl carbon. The carbonyl carbon of both aldehydes and ketones is electrophilic.

Aldehyde Ketone

O O

H δ δ

H atom C atom C atom C atom

NOMENCLATURE OF ALDEHYDES AND KETONES IUPAC The parent of an aldehyde or ketone is the longest, continuous carbon chain that contains the carbonyl carbon of the functional group. The parent name reflects the total number of carbon atoms in the chain (2 carbons = ethan, 3 carbons = propan, etc..). The parent chain is numbered from one end of the chain, so as to give the carbonyl carbon the lowest possible number. For aldehydes, this means the carbonyl carbon will always be the number 1 carbon. Substituents are assigned a number to indicate their position on the parent chain. Substituents are named to reflect the number of carbon atoms of the substituent. Substituents are placed in alphabetical order. The “-AL” suffix is used for aldehydes, the “–ONE” suffix is used for ketones.

O

O O CH3

H

3-methylbutanal 4-methylhexanone Cl

4-chloro-2-methylcyclohexanone

Organic Chemistry Lecture Outline Carbonyl-Containing Functional Groups

COMMON There are many common names that are used to describe aldehydes and ketones. Some of these are:

O O O

CH H 3

Benzaldehyde Acetophenone methylethyl ketone

O O O

H H H H3C CH3

Formaldehyde Acetone Acrolein

REACTIONS TO PREPARE ALDEHYDES & KETONES ALDEHYDES 1. Oxidation of Alcohols O

PCC H

OH O

Jones Reagent OH 2. Reduction of Esters DIBAL is used to reduce esters to aldehydes

Ester Aldehyde

O O O DIBAL OR ROR + ROR RH H HOH H Tetrahedral Intermediate ROH

3. Hydration of Terminal Alkynes

H2B H = H2B H

BH3 H CCCH3 H H CH3 CH3

Transition State H2O2 NaOH

O H HO H H

H CH H 3 CH3 Aldehyde Enol Organic Chemistry Lecture Outline Carbonyl-Containing Functional Groups

KETONES 1. Oxidation of Alcohols O

PCC

O

OH Jones Reagent

O

Na2Cr2O7 2. Friedel-Crafts Acylation Cl Cl

Cl Al Al Cl O O Cl X R X R

AlX3

O O H

R R

3. Hydration of Terminal Alkynes

H H + OH2 H3O H CCCH3 H CH3 H CH3 Most Stable Carbocation Oxonium ion

H O H OH H

H CH H 3 CH3 Ketone Enol

CARBOXYLIC ACIDS, ESTERS AND AMIDES Carboxylic acids, esters and amides are carbonyl-containing functional groups. The structures and reactivity of these functional groups are similar. Carboxylic acids have a hydroxyl group (-OH) and a carbon atom bonded to the carbonyl carbon. Esters have an alkoxide group (-OR) and a carbon atom bonded to the carbonyl carbon. Amides have an amino group (-NH2, -NHR, -NR2) and a carbon atom bonded to the carbonyl carbon. The carbonyl carbon of all of these functional groups is electrophilic, but not as electrophilic as aldehydes and ketones.

Organic Chemistry Lecture Outline Carbonyl-Containing Functional Groups

Carboxylic Acid Ester

O O

HO δ RO δ

hydroxyl C atom Alkoxide C atom group group

Primary Amide Secondary Amide Tertiary Amide O O O

H N δ R N δ 2 RHN δ 2

amino C atom amino C atom amino C atom group group group

STERIC AND ELECTRONIC EFFECTS OF CARBONYL COMPOUNDS Steric Effects Steric effects influence the reactivity of the electrophilic carbonyl carbon in nucleophilic acyl addition and nucleophilic acyl substitution reactions. Carbonyl groups bonded to large, bulky substituents (eg., tertiary carbons) react slower with nucleophiles than carbonyl groups with smaller, less bulky substituents.

Electronic Effects Electronic effects influence the reactivity of the electrophilic carbonyl carbon in nucleophilic acyl addition and nucleophilic acyl substitution reactions. Substituents with lone pair electrons assiociated with them can donate electrons into the pi system, making the electrophilic carbonyl carbon less positive and less reactive with a nucleophile. Carbonyl-containing functional groups like carboxylic acids, esters and amides that have substituents with lone pairs (O or N atoms) react slower than aldehydes and ketones due to this electronic effect.