organic chemistry reactions
DESCRIPTION
Organic Chemistry Reactions. Condensation RXNs and Elimination RXNs. Condensation - Esterification. Condensation: Reactions in which water is eliminated Esterification : ester formed by combining an alcohol and carboxylic acid . Ex : Combine propanol with ethanoic acid: - PowerPoint PPT PresentationTRANSCRIPT
Condensation RXNs and Elimination RXNs
ORGANIC CHEMISTRY REACTIONS
Condensation - Esterification• Condensation: Reactions in which water is eliminated • Esterification: ester formed by combining an alcohol and carboxylic acid.
• Ex: Combine propanol with ethanoic acid:•
• Methanol Ethanoic acid Methyl ethanoate Water
• –OH group from alcohol combines with H from the carboxylic acid to form H2O
• New bond between O from carboxylic acid and C from alcohol
O C C
O H
H
HH C OH
H
H
C O
H
H
C C
O H
H
HH+
H2 O
H + H2 O
This bond is part of the alcohol
This bond is partof the acid
This is the new bond
Condensation - Esterification• Ester name is derived from the original alcohol and carboxylic acid• Alcohol is the first part of the name ( –anol becomes –yl)• Carboxylic acid is the second (-anoic acid becomes -anoate)
• Thus, methanol and ethanoic acid form methyl ethanoate
• Reaction is catalyzed by concentrated sulfuric acid• Typically sweet smelling
• Used as artificial flavoring agents• Have no –OH groups,
• NOT very soluble in water• Don’t have the ability to hydrogen bond • Unlike the original alcohol and carboxylic acid
Condensation - Polymerization• If the monomer contains two different functional groups, it can undergo a type of polymerization called condensation polymerization• A small molecule (often water) is released each time two
monomers come together.
• Ex. Synthesis of proteins from amino acids:•
• Amino acid – has an amine and a carboxylic acid• The two functional groups attached to a chiral carbon• Also bonded to a hydrogen atom and a unique side chain (represented by “R”)
• This side chain, R, is different for each amino acid (20 different amino acids, each with a different “R” group)
OHCC
O
N
H
H
H
Ramine group carboxylic acid group
side chain
Condensation - Polymerization• Amino acid – has an amine and a carboxylic acid
Condensation - Polymerization• When two amino acids come together
• “H” is lost from the amine group and the “OH” is lost from the carboxylic acid group
• This is a water molecule• New bond formed between the nitrogen in the amine group
and the carbon in the carboxylic acid group = peptide bond or peptide linkage
• Molecule is called a dipeptide• Can combine with other amino acids to eventually form a long
chain of amino acids called a protein.
OHCC
O
N
H
H
H
H
OHCC
O
N
H
H
H
CH3
CC
O
N
H
H
H
H
OHCC
O
N
H H
CH3
H2 O
peptide bondglycine alanine
Condensation - Polymerization• Optical isomerism in amino acids• Called the “L” form and one called the “D” form• Living organisms most proteins made of “L” form• Synthetic creation = a racemic mixture• Other examples of condensation polymers include nylon and polyester
• An example of the formation of a polyester:
Condensation vs Dehydration
• Condensation:• Possible small molecules lost are water, hydrogen chloride,
methanol, or acetic acid but most commonly in a biological reaction it is water.
• Often intermolecular (bonds 2 molecules together)
• Dehydration is a subset of Condensation (a type of)• Removes a water molecule from a larger molecule• Often needs a Bronstead acid catalyst
Elimination vs Substitution• Elimination reactions are similar to substitution reactions
• The differences:• In elimination, the halogen is removed along with a hydrogen atom• Creating an alkene
• In substitution, the halogen in a halogenoalkane is replaced with an –OH group• Creating an alcohol
• Difference of temperature• Substitution (60°C) vs elimination (100°C)
• Substitution occurs in a dilute solution of hydroxide ion• Elimination reactions occur in a higher concentration of hydroxide ions in ethanol
Elimination of halogen from haloalkane• Elimination of bromine from bromoethane:• A concentrated solution of hydroxide ion in ethanol is heated to approximately 100°C
• The hydroxide ion (strong base) is able to remove a hydrogen ion from the –OH group on the alcohol
• Creates molecule of water and an ion called the ethoxide ion (C2H5O-) (a strong base)
C C
H
H
H
H
H O H C C
H
H
H
H
H O:. .
. .:O: H
-
. .
. .:O: HH:
-
Elimination of halogen from haloalkane• Next, the ethoxide ion “attacks” a hydrogen atom on the bromoethane
molecule. Specifically, a hydrogen on the carbon adjacent to the bromine-containing carbon is attacked:
• ethoxide ion bromoethane ethanol ethene bromide ion
• The “curly arrows” are showing the movement of electron pairs• Ethoxide (strong base) removes a hydrogen ion from the bromoethane
molecule (the “attack”)• Electrons in the bond between this H and C remain with carbon (remember,
removed hydrogen ion)• Those two electrons move to form a double bond between the 2 C atoms• Increased electron density repels the electrons in the carbon-bromine bond
away• These electrons end up moving completely to the bromine atom to form a
bromide ion• This “eliminates” bromine from the bromoethane
C C
H
H
H
H
H BrC C
H
H
H
H
H O C C
H
H
H
H
C C
H
H
H
H
H O H Br:-
: + +