The Claisen Condensation: Formation of !-Ketoesters
from Esters with Enolizable Hydrogens
Esters with enolizable H undergo a reaction similar to the aldol
condensation in the presence of alkoxide bases.
enolate anion of ester
Addition of Derivatives of Ammonia, H2N-G
Derivatives of ammonia, H2N-G, react with aldehydes and ketones
under acid-catalyzed conditions to produce imines.
A Mechanism for Imine Formation
Disaccharides are carbohydrates made up of two monosaccharides
joined through an acetal linkage. Hydrolysis of a dissacharide
yields the two monosaccharides.
glucose + glucose
glucose + gala
Substituent Effects on the Reactivity and Orientation
of Electrophilic Aromatic Substitution
Substituent groups already on the benzene ring greatly influence
both the reactivity of electrophilic attack, and the site (o,m,p) of
attachment of the incoming e
Nucleophilic Addition to the Carbon-Oxygen Double Bond
The reactivity of the carbon-oxygen double
bond is determined by the polarization:
Because of the permanent dipole, nucleophiles add to the
electropositive carbon and electrophiles add t
Chapter 24: Carbohydrates!
The name carbohydrates is derived from the general formula Cx(H2O)y
that seems to suggest "hydrates of carbon." Structurally, they are
polyhydroxylated aldehydes or ketones that exist in cyclic hemiacetal
Reactions at the -Carbon of Carbonyl Compounds!
Enols and Enolates!
and Unsaturated Carbonyl Compounds!
Acidity of the !-Hydrogens of Carbonyl Compounds
Hydrogens ! to the carbonyl group are much more acidic than
ordinary aliphatic hydrogens t
The Hofmann Rearrangement: Amines from Primary Amides
Primary amides are converted into amines with loss of the carbonyl
carbon atom in aqueous basic solutions of Br 2 or Cl2.
RCNH2 + X2 + 4 NaOH
RNH2 + 2NaBr + Na2CO3 + 2 H2O
The Hofmann r
Amino Acids, Peptides, and Proteins!
Proteins come in a wide variety of shapes and sizes. They all are
polymers of !"amino acids. The amino acid units are held together
with amide bonds. Proteins are polyamides.
Amides like amines are classified
according to the structure around
the nitrogen :
Synthesis of Amides from Acyl Chlorides
Chapter 23: Amines!
Amines are organic bases. They are found widely in nature.
Trimethylamine occurs in animal tissue while the distinctive odor
of fish is due to amines. Amines isolated from plants are called
many of which are pha
Nucleophilic Substitution at Acyl Carbon
Aldehydes and ketones undergo nucleophilic additions
to the carbonyl group:
C-O-H + Nu:Nu
The typical reaction with carboxylic acids and
Aryl Halides, Nucleophilic Aromatic Substitution,
Simple aryl halides do not
easily undergo nucleophilic
Similarly, vinylic halides do not react under these conditions.
Some Problems with the Open-Chain (Fischer)
Structure for D-(+)-Glucose
The open-chain aldose structure is not
consistent with some of the chemical
and physical properties of glucose.
the Fischer structure HO
The Acetoacetic Ester Synthesis of Substituted Acetones
A synthetic sequence starting from ethyl acetoacetate is a standard
way to prepare methyl ketones (substituted acetones). It is called
the acetoacetic ester synthesis.
Aldehydes and Ketones: Carbonyl
General Features of the Carbonyl Group
The general structure of
the carbonyl group is
In a molecular orbital description, the carbon and oxygen atoms
are hybridized sp2. A sigma
Nitration of Benzene
Benzene reacts only slowly with hot concentrated nitric acid to give
nitrobenzene. The reaction is much faster in a mixture of
concentrated nitric acid (pKa = -1.3) and concentrated sulfuric acid
(pKa = -9), a much stronger acid.
Some Other Reactions of Monosaccharides
Enolization, Tautomerization and Isomerization
When D-glucose is dissolved in an aqueous solution of calcium
hydroxide and allowed to react for a few days, several products are
recovered including D-mannose (an aldo
Chapter 16 and Chapter 17!
Synthetic Strategies with EAS and Reactions of the Benzene Side Chain!
Modification of Amino and Hydroxyl Groups by Acetylation
These groups are highly activating in electrophilic aromatic
Reactions of Aromatic Compounds
Aromatic Substitution Reactions
The chemical reactivity of benzene is characterized by substitution
rather than addition, which preserves the aromatic ring.
Electrophilic, aromatic substitution.