Organic Chemistry Reactions

1. Organic Chemistry Reactions Condensation RXNs and Elimination RXNs

2. Condensation - Esterification • Condensation: Reactions in which water is eliminated • Esterification: ester formed by combining an alcoholandcarboxylic acid. • Ex: Combine propanol with ethanoic acid: • MethanolEthanoic acid Methyl ethanoateWater • –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

3. 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, methanoland 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

4. Condensation - Polymerization • If the monomer contains twodifferent 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)

5. Condensation - Polymerization • Amino acid – has an amine and a carboxylic acid

6. 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.

7. 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:

8. 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

9. 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

10. 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)

11. 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: • ethoxideion bromoethaneethanolethene bromide ion • The “curly arrows” are showing the movement of electron pairs • Ethoxide (strong base) removes a hydrogen ion from the bromoethanemolecule (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