Organic chemistry Lab
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1. IR spectroscopy Lab
How do you prepare a solid KBR sample for IR?
KBR Pellet to prep Solids
- 1. Need Dry Sample
- 2. Put a small amount of KBr in a 10 ml Beaker
- 3. 3. Small amount of solid sample [1:10 ratio]
- 4. Grind together and screw in lower piston/nut
- 5. Scoop enough sample to cover head of piston
- 6. screw the 2 pistons until firmly sandwiched between the two pistons
- 7. use wrenches to get Tighter
- 8. allow for 3 min to sit
- 9. Unscrew , remove pistons, indie nut should be a hardened film
- 10. pellet should be translucent
Using a Die-press Kit
How to prepare a salt plate for IR with liquid Samples?
- Clean the plates with CH2Cl2; rub in circular motion with a paper towel
- - Make sure it has all evaporated to avoid mixture
- -add 1-2 drop of sample between plates
- ( liquid should form a film between the two plates)
Index of HDI equation to determine saturation:
The number of double bonds or rings within a compound.
William Ether Synthesis Theory mechanism
- Add water soluble pheonixide Salt
- alkyl halide is not soluble in aqueous
- solution; addition of substrate [BENZYL
- BROMIDE] must be counteracted with catalyst
- [TETRABUTYLAMMONIUM BROMIDE] to bring
- reactants together to react
What is the purpose of the Phase Transfer Catalyst in Williamso Ether Synthesis ?
Brings Phenoxide ion into organic phase layer composed of Benzyl Bromide molecules.
William Ether synthesis:
Isolation of the product Method : Aqueous and Organic Phases of Williamson Ether synthesis
-sodium phenoxide salt = AQUEOUS LAYER
-benzyl bromide = ORGANIC LAYER
- -after reflux and addition of diethyl ether, the
- ORGANIC layer is NOW ON TOP because ether is very light and less dense than the aqueous layer
-aqueous now the bottom more dense layer
Williamson Ether Synthesis
How to dry Organic Layer?
The Diethyl Ether layer that contains the product must be dried to remove any xs water in the organic layer . The drying process is performed using sodium sulfate and the filtration column.
The microfilteration column to dry the product consists of sodium Sulfate. Sand , cotton plug loosely packed using a pasture pipet.
Specific Mechanism of Williamson Ether Synthesis:
- Step 1 : Formation of alkoxide Ion
- R-O-H + M --> R-O- +M + 1/2H2
- -alcohol + metal --> positive metal pulls H and ionically bonds to O-
- step 2: SN2 mechanism
- -alkoxide ion attacks C, displaces X, yields ether +
Williamson Ether Synthesis
After extraction positions of Organic and Aqueous layer:
After 1 hour reflux 2 layer were observed
- Aqueous layer - Bottom
- ( sodium Phenoxide salt)
- Organic Layer - Top
- Benzyl Bromide
Sodium Borohydride Reduction of Ketone Theory
Aldehyde and ketones can be reduced to form alcoholsPrimarily use LiALH4 or NaBH4Can reduce by either adding a hydrogen or removing an oxygen
Sodium Borohydride Reduction of Ketones
- Less reactive - mild reducing agent
- safe to handle
- use in protic or aqueous solvents ( like alcohols)
- Reacts slowly with Neutral water and is stable in basic solution
- Unreactive to other functional groups listed for reactivity to lithium aluminum hydride.
Borohydride Reduction of Ketones La
- Very reactive and powerful reducing agent
- Handled carefully
- used in aprotic solvents
- Reacts violently with water and other hydroxyl solvents to produce Hydrogen gas
- - Reactive towards most aldehydes, ketones, esters, epoxides, nitriles, and nitro groups.
Sodium Borohydride reduction of Ketones
Ketone or Aldehyde + NaBH4 +4 (OH group) and heat to give a secondary Alcohol group.
Sodium Borohydride reduction of Ketones:
Isolation- why HCL?
HCl to remove excess NaBH4 from product.
Theory of Forming Grignard Reagent
Glassware and lab items free from Water
- H2O water is detrimental to reaction
-prepared with the reaction of a
- magnesium metal with an alkyl halide,
- vinyl halide, or an aryl halide in an ether
- solvent like THF or diethyl ether
- -very sensitive to presence of wate
Grignard Reaction Lab
Why is water so detrimental to the Reaction ?
- H2O is detrimental to reaction
- - Water will act like an acid and react with Mg which acts as a base and form MgBrOH . This will result in different reactions when Methyl Benzoate mechanism is added and not the desired one.
How to calculate Theoretical yield given the Moles of starting material:
Fischer Esterification Lab Mechanism
-used to prepare esters via a condensation of
- a carboxylic acid and an alcohol
- -strong acid is used in this reaction as a
- catalyst for the condensation to take place
- -THE REACTION IS ACID-CATALYZED
- -THE REACTION IS REVERSIBLE
Fischer Esterification Lab: Theory
reversible=should not expect a high
- -direct esterification of acetic acid with
- isopentyl alcohol yields isopentyl acetate
- -can shift equilibrium towards ester by
- using excess of one starting material
- [alcohol or acid]
How to shift the equilibrium to the formation of the product.
Control the substrate quantity to control the forward the reaction in two ways.
- 1. Excess one of the reactants to move it forward- so one limiting and the other excess
- 2. Removing H20 to get the forward as it forms through distillation
a,b Unsaturated Ketone Mechanism
- Step 1: Base catalyzed formation of an
- enolate anion
- Step 2: Michael Addition
- Step 3: Tautomerization
- Step 4: Formation of a second enolate
- anion [base catalyzed]
- Step 5/6: Aldol Condensation
a,b-unsaturated Ketone: Michael Addition
a carbanion attacks carbocation ( beta carbon)
NaOH --> enolate anion Formation --> nucleophile to attack beta carbon
a,b Unsaturated Ketones
Importance of Beta carbon
Ethoacetate --> Acts as a nucleoyphole in presence of naps - it precipitates
Preparation of a,b-unsaturated Ketone
Aldol Condensation Step
Part 1: Primary Carbanion attacks intramolecularly the C=O; ring formation with enolate ion. A 6 member ring is more stable
Part II: O- grabs H fro water : Dehydration and double bond formation ( E2)
Diazo Imaging Lab
Role of Ammonia and Halogen Lamp in developing image.
The light allows the unstable diazonium salt to break down in the area that light passes through the film.
Ammonia vapors will allow for the exposure of colors. Salt wont break down and coupling reaction occur underneath the dark image.
DiazoImaging: Need to know about the function of activated aromatic in Diazoimaging experiment.
- Activated Aromatic compounds :
- An activated aromatic compound is an aromatic ring with strong electron donating groups. The arene is strongly activated and acts a nucleophile to attack the Electrophilic diazonium salt.
- Electrophilic aromatic substitution
- Ex: OH, OR NH2, Alkyl
activated methylene compounds function
- compounds that are highly acidic and can be deprotonated via a base.
- Because of the conjugate base is highly stabilized through resonance.
Activated aromatic compounds in experiment
Activated Methylene Compounds
Condensation Polymers Mechanism
- which are formed
- when monomers are linked together with the release of a smaller molecule, such as water or
- hydrogen chloride.
- joined to each other
- by covalent bonds through a process known as crosslinking
- The amide bond which connects the monomers in the nylon molecule is the same kind of bond
- that is found in proteins where it is referred to as a peptide bond
Characteristics of an ideal crystallization
- a good solvent in a temperature vs solublility function -
- very soluble at elevated temperatures
- Sparingly soluble at room temperature.
Melting Point - When there is impurities it lowers or broadens the melting point
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