Ochem Lab Final

What differences exist between the fractional distillation apparatus and the simple distillation apparatus?
In fractional distillation, the “fractionating column” is added to the apparatus, which results in condensation and revaporization of the substance.
What fundamental difference(s) exist between simple and fractional distillation?
In fractional distillation, the “fractionating column” causes vapor to condense and then revaporize multiple times. Each time this occurs is equivalent to one simple distillation.
What is an azeotrope?
A mixture of liquids with constant composition.
What is the composition of a water-ethanol azeotrope?
There is 95.6% ethanol and 4.4% water in an water-ethanol azeotrope.
What is the maximum purity of ethanol that can be achieved when distilling from a water-ethanol mixture?
No number of distillations, however, will ever result in a distillate that exceeds the azeotropic ratio. Thus, there will be 95.6% ethanol and 4.4% water.
Is D-limonene polar or nonpolar?
Non-polar
What allowed the CO2 to liquefy in the experiment with D-limonene?
The use of dry ice kept it at a low pressure and temperature, which allowed us to control the phase change.
What is the stationary phase in TLC?

Adsorbents- stationary phase that interacts with the

compound(s).

 

1. silica gel (Si02) – slightly acidic and good for a broad range of compounds

 

2. Alumina (Ab03) – slightly basic and used when a basic

compound will not run well on a silica.

 

Most plates have a plastic, glass, or aluminum backing with a thin layer of silica, which contains a binding agent to keep it bonded to the backing. 

Is ethyl acetate or hexane the more polar solvent?
Ethyl acetate
How does increasing the percentage of ethyl acetate in the mobile phase of TLC affect the Rf value?
Ethyl acetate would cause advancement up the silica to cease.
Define Rf with an equation and define terms

Rf= Distance traveled by eluent/distance traveled by solvent.

 

Eluent: spot

Is benzyl alcohol an H-bond acceptor?  Is it a donor?  
It is an acceptor
Is benzaldehyde an H-bond acceptor or donor?
Acceptor
Does benzyl alcohol or benzaldehyde have a larger Rf in a given ethyl acetate-hexane mixture?   Why? 

The order of elution in silica gel chromatography generally follows the order of polarity. More polar compounds are retained on the silica gel and will have lower

Rf values. The least polar compound, benzaldehyde, is expected to be eluted first; then benzyl alcohol and finally benzoic acid. 

1. How did we visualize spots in the TLC experiment?  Will this work for all molecules?  

We looked at them under UV light. The TLC plate contains a fluorescent indicator, and compounds that absorb UV light will hide the fluorescence in that spot, showing up as a purple or blue smear. This should work for any compound that absorbs UV light.
Equation for Theoretical Yield Calculation

Theoretical Yield: 

 [(limiting reagent)*(1 mol reagent/MW reagent)]*amount of product

 

Equation for Percent Yield Calculation
(Amount of product produced/theoretical yield)*100%
In bromination of stilbene, Why is the product a meso molecule rather than a racemic mixture?

The product of this reaction, 1,2-dibromo-1,2 diphenylethane, has two stereogenic centers which normally leads one to predict four (2n= 22 in this case) possible stereoisomers (i.e., four optical isomers). However, there are only three possible isomers in the case of 1,2-dibromo-1,2-diphenylethane since one, the so-called meso isomer, is superimposable on its mirror image. The meso isomer does contain stereogenic centers, but since it is superimposable on its mirror image, it does not rotate the plane of polarized

light.

 

In the bromination of stilbene, how did we generate molecular Br2?  Give the balanced reaction. 

HBr+H2O2-> Br2+ 2 H2O

 

Why does more isoborneol form in the camphor reduction?
Isoborneol is the exo product. Since the endo product is more sterically hindered, Isoborneol is formed.
In adipic acid synthesis, describe the role of each; sodium tungstate, hydroperoxide, and aliquat. 

Sodium Tungstate: Oxidizing Agent

Hydroperoxide: Oxidative Cleavage

Aliquat: Catalyst

What is the purpose of recrystallization of adipic acid?
Purification
Describe the step-wise procedure for recrystallizing adipic acid from water.  

1. Dissolve the liquid

2. Remove any insoluble impurities

3. Crystallization

4. Isolation of crystals

How did we assess purity

of the adipic acid experimentally?   

Compared the experimental melting point with the literature melting point.
What is the structure of D-limonene extracted from orange peel?
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What is the structure of ethyl acetate?
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What is the structure of hexane?
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What is the mechanism associated with the bromination of trans-stilbene?
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What is the mechanism of the camphor reduction to borneol/isoborneol?
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What is the structure of sodium tungstate?
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What is the structure of hydroperoxide?
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What is the structure of aliquat?
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What does the set up for simple distillation look like?
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What does the fractional distillation apparatus look like?
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What does a vaccuum filtration set up look like?
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What does a reflux apparatus look like?
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