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ALDEHYDES AND KETONES I. NUCLEOPHILIC ADDITION TO CARBONYL. Chapter 16. Reading Assignment. DO: Sections 16.0 through 16.7 SKIP: Section 16.8 DO: 16.9 through 16.18 SKIP: Section 16.19 DO: Section 16.20 Organic Nomenclature: Aldehydes and Ketones. Problem Assignment.
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ALDEHYDES AND KETONES I.NUCLEOPHILIC ADDITION TO CARBONYL Chapter 16 WWU Chemistry
Reading Assignment • DO: Sections 16.0 through 16.7 • SKIP: Section 16.8 • DO: 16.9 through 16.18 • SKIP: Section 16.19 • DO: Section 16.20 • Organic Nomenclature: Aldehydes and Ketones WWU Chemistry
Problem Assignment • In-Text Problems • 16.1 through 16.27 • End-of-Chapter • 1 through 6 • 7a; 7c through 7j • 8 b, c, d • 9 through 10 • 12 through 14 WWU Chemistry
Aldehyde Ketone WWU Chemistry
IUPAC Nomenclature of Ketones • Choose the longest continuous carbon chain that contains the carbonyl carbon • Number from the end of the chain closest to the carbonyl carbon • Ending is -one • Do the ketonessection of Organic Nomenclature -- Assignment! WWU Chemistry
Example 2-Pentanone WWU Chemistry
Another... 4-Ethyl-3-hexanone WWU Chemistry
And another... 3-Isopropylcyclopentanone or 3-(1-Methylethyl)cyclopentanone WWU Chemistry
Common, or Trivial, Names • Name each group attached to the carbonyl group as an alkyl group • Combine into a name, according to: • alkyl alkyl’ ketone • NOTE: This is not all one word! WWU Chemistry
Example of a Common Name Methyl propyl ketone WWU Chemistry
Another example... Diethyl ketone WWU Chemistry
Important example! Dimethyl ketone Acetone WWU Chemistry
Another Important Common Name Acetophenone (Methyl phenyl ketone) WWU Chemistry
IUPAC Nomenclature of Aldehydes • Choose the longest continuous carbon chain that contains the carbonyl carbon • Number from the end of the chain closest to the carbonyl carbon (this will automatically be carbon #1!) • Ending is -al • Note: The carbonyl carbon is not identified by number in the final name. • Do the aldehydessection of Organic Nomenclature -- Assignment! WWU Chemistry
Example Hexanal Notice that there is no “-1-” in the name! WWU Chemistry
… another: 5-Methylhexanal WWU Chemistry
One more: 3-Phenylpropanal WWU Chemistry
For cyclic molecules, the ending is -carbaldehyde Cycloheptanecarbaldehyde WWU Chemistry
Two acceptable alternative names: Benzenecarbaldehyde (official IUPAC name) Benzaldehyde (acceptable IUPAC name) WWU Chemistry
Common Names of the Aldehydes WWU Chemistry
Forming Common Names of Aldehydes WWU Chemistry
Also: “Iso” names: • Whenever there is a -CH(CH3)2 group, an alternative common name is an “iso” name. • The “iso” name includes all of the carbon atoms in the molecule. • The “iso” name isn’t used if there are other substituents. WWU Chemistry
Example b-Methylbutyraldehyde Isovaleraldehyde WWU Chemistry
Another example... e-Bromocaproaldehyde w-Bromocaproaldehyde WWU Chemistry
Benzaldehyde ortho (o-) meta (m-) para (p-) 1,2- 1,3- 1,4- WWU Chemistry
More than one subsituent: 4-Hydroxybutanal g-Hydroxybutyraldehyde The prefix for -OH is hydroxy WWU Chemistry
Also... 2-Methoxypentanal a-Methoxyvaleraldehyde WWU Chemistry
Bourgeonal is thought to be a chemoattractant emitted by the egg and detected by an odor receptor on the sperm cell. This guides the sperm to the egg Science, 299, 2054 (2003) WWU Chemistry
Structure of the Carbonyl Group • Hybridization of the carbonyl carbon is sp2. • Geometry of the carbonyl carbon is trigonal planar • Attack by nucleophiles will occur with equal ease from either the top or the bottom of the carbonyl group. • Hybridization of the oxygen is “nominally” sp2. WWU Chemistry
Prochiral The carbonyl carbon is prochiral. That is, the carbonyl carbon is not the center of chirality, but it becomes chiral as the reaction proceeds. These two products are enantiomers. In general, both enantiomers are formed in equal amount. WWU Chemistry
Reaction of the Carbonyl Group with Acids Typical behavior WWU Chemistry
Reaction of the Carbonyl Group with Bases Typical behavior WWU Chemistry
Nucleophilic Addition to Carbonyl -- General Mechanism NOTE: Reversible reaction WWU Chemistry
Nucleophilic Addition to Carbonyl -- in Acid (General Mechanism) NOTE: Reversible reaction WWU Chemistry
The carbocation intermediate has resonance. The positive charge character on carbon makes this an excellent site for attack by Lewis bases (nucleophiles). WWU Chemistry
Once we have the intermediate, what happens to it? Case 1: The Addition Product is Stable. The reaction stops here. This happens most often when the nucleophilic atom is carbon, oxygen, or sulfur. WWU Chemistry
Case 2: Addition-Elimination The addition product is unstable with respect to loss of a molecule of water. This is observed most often when the nucleophilic atom is nitrogen or phosphorus. WWU Chemistry
Case 3: Loss of Leaving Group This process is observed when X is a potential leaving group. In this case we have nucleophilic acyl substitution (see Chapter 19). WWU Chemistry
What are the stereochemical requirements? • The hybridization of carbon in the carbonyl group issp2 • The geometry around carbon is trigonal-planar. • Nucleophile can attack the carbonyl group equally easily from top or bottom (see model) • BUT: aldehydes react faster than ketones in nucleophilic addition! WWU Chemistry
Why? • Aldehydes have a hydrogen attached to the carbonyl group, whereas ketones have an alkyl group. • Alkyl groups are much more bulky than hydrogens -- hence ketones should show some steric hindrance. • Alkyl groups have a small electron-releasing inductive effect. • This should make the carbonyl carbon less favorable by attack by nucleophile. • The answer is that there is a combination of steric hindrance and inductive effects that makes ketones react slower than aldehydes. WWU Chemistry
Addition of Cyanide (16.6) A cyanohydrin WWU Chemistry
Mechanism WWU Chemistry
Example • Notice that the cyanide ion and the acid are added in two separate steps! • Sodium carbonate is used to keep the reaction medium basic. WWU Chemistry
So, what’s it good for? Nitriles can be hydrolyzed to form carboxylic acids. This affords us with an important method of synthesizing a-hydroxy-carboxylic acids -- important intermediates in biochemical processes. WWU Chemistry
Reaction with Organometallic Compounds (16.7) The products of this sequence are always alcohols. WWU Chemistry
Addition of Organometallic Reagents The products of the addition are always alcohols. WWU Chemistry
Crude outline of the mechanism of organometallic addition WWU Chemistry
Whatever is attached to the carbonyl group will be attached to the resulting alcohol carbon. WWU Chemistry
Example Organometallics react with ketones to yield tertiary alcohols. WWU Chemistry
And another... Organometallics react with aldehydes to form secondary alcohols WWU Chemistry