Organic Chemistry 1 Lab Final Notes

What is the purpose of recrystallization

purify solids

What is the purpose of heating up the solvents for recrystallization

increase solubility

How much hot solvent should be added to recrystallize a solid

enough so solid is dissolved and solution is saturated

How should the solid being recrystallized behave in the chosen solvent at different
temperature in order to carry out a successful crystallization

at low temperatures the solid should not dissolve, but at high temperatures the solid
should dissolve in the solvent

How should you cool your hot recrystallization solution to get the largest and most pure
crystals possible?

slowly letting it get to room temperature and placing in ice bath

What is the name of the process that occurs when a solid changes to a liquid

melting

What is the main reason that we care about the melting point of a solid?

it shows purity of the solid and allows us to identify it

how should you report a melting point?

range

What is the phenomenon of reduction of the melting point of a compound caused by the
presence of impurities?

melting point depression

What should you do if too much solvent has bee used and crystals do not form when the solution is cooled?

boil off the solvent to re-saturate the solution

If you perform this bromination-debromination process on cyclohexene, the final product
obtained is not an alkyne. Why not? What is the most likely structure of the final produ

Cyclic alkynes are highly strained and not easy to form

In the reaction of bromine with trans-stilbene, which stereoisomer(s) of the vicinal dibromide
can be formed?

a single meso compound

Why does bromine act as an electrophile in the reaction with alkenes?

Its bond polarizes in the presence of the alkene pi-electrons

What functional group is formed after two dehydrohalogenation reactions of a vicinal
dibromide?

alkyne

During the electrophilic addition of Br₂ to alkenes, why must the bromide ion attack from the
backside of the bromonium ion?

maintain anti-addition stereochemistry

Explain why the reaction of Br₂ with an alkene is stereospecific and what type of product is
formed.

backside is needed to form vicinal dibromide

During preparation of stilbene dibromide, you are treating the filtrate with water and adding
enough sodium bisulfite to remove any orange color before discarding in the sink.

What causes orange color?

Bromide formation

During preparation of stilbene dibromide, you are treating the filtrate with water and adding
enough sodium bisulfite to remove any orange color before discarding in the sink.

What are we trying to get rid of?

Bromine

During preparation of stilbene dibromide, you are treating the filtrate with water and adding
enough sodium bisulfite to remove any orange color before discarding in the sink.

What is the chemical reaction involved?

Redox reaction

What is a lachrymator? Why is it important to be aware of this?

chemical that makes eyes burn

When does the boiling point range begin?

when first drop is collected

When boiling a pure compound what is the relationship of the pot temperature and the head
temperatur

The pot temperature is the same as the head temperature

Raoult's Law states that the partial vapor pressure of a component in a mixture is directly
proportional to:

the mole fraction of the component in the mixture

Dalton's Law explains that the mole fraction of a component in the vapor phase is equal to
the ratio of its:

vapor pressure in the mixture to the total vapor pressure

What is the theoretical plate in fractional distillation?

single step in series of simple distillations

In simple distillation, how many theoretical plates are typically involved?

1

Which of the following compounds has the lowest boiling point?

n-hexane

When should simple distillation be used instead of fractional distillation?

When the boiling point difference between the compounds is 110°C or more

If a mixture contains equal amounts of carbon tetrachloride and toluene, the vapor phase will
contain:

more carbon tetrachloride

Which statement is true about the heating mantle used in distillation?

It should never come in contact with liquid

Consider this boiling point-composition curve for Cyclohexane and Toluene.

At a temperature of 1050C, what is the approximate vapor mole ratio of cyclohexane to
toluene?

40:60

Consider this boiling point-composition curve for Cyclohexane and Toluene.

Explain the main differences between simple distillation and fractional distillation

Fractional distillation is used to separate liquids with similar boiling points

Consider this boiling point-composition curve for Cyclohexane and Toluene.

Explain the role of a theoretical plate in fractional distillation

Provides additional distillation events that help differentiate two boiling liquids and enhances purity of distillate

Consider this boiling point-composition curve for Cyclohexane and Toluene.

Why is it important to ensure a steady flow of cooling water through the condenser during
distillation? What could happen if there is not an adequate flow?

steady flow allows condenser to condense the vapors to a liquid, too little flow would result in less distillate collected

Observation A:B = 1 has what mechanism?

Both SN1 and SN2 observed

Observation A:B > 1 has what mechanism?

SN2 fastest

Observation AB < 1 has what mechanism

SN1 fastest

Ethanol and 2,6-dimethylphenol both have OH groups and can be protonated by a base. Why
does ethanol act as a solvent and not as a Nu- under the conditions in this experimen

Phenol is more acidic and more rapidly deprotonated

What is the purpose of washing the organic solution with 1M aqueous NaOH during the
workup procedure?

Remove phenol starting material left over in the reaction

Using a max of 2-3 sentences, describe the technique of reflux and why it is important?

Reflux coupled with a reflux condenser allows rxn to boil without all the solvent evaporating

What is the primary solvent used in the extraction of the active ingredient from an analgesic drug?

Methanol

Which technique is employed to separate fine particles of binder from the active ingredient after diffusion?

centrifiguation

Which of the following steps is NOT part of the procedure for extracting the active ingredient
from the analgesic drug?

Adding hydrochloric acid

What is the significance of using a Hirsch funnel in the procedure?

dry crystals

Which observation is NOT considered the start of the melting point range during the analysis?

solid becomes shiny

Why is it important to complete the evaporation procedure within 10-15 minutes?

Avoid decomposition of the drug

If the liquid collected after column chromatography is still cloudy, what should be done?

Rerun samples thru new silica gel

What is the purpose of adding an additional 1 mL of methanol to the column after the initial
liquid has passed through?

Ensure all the drug has been eluded from column

During the evaporation of the solvent, why is a gentle stream of dry air directed into the vial
containing the liquid?

Speed up evaporation process

Which step ensures the separation of the supernatant liquid from the solid residue after centrifugation?

Carefully transferring the liquid phase to a test tube

What is the main purpose of using column chromatography in the isolation procedure?

Purify active ingredient from mixture

In the context of this experiment what does term "elution" refer to?

Sending a solution thru the column

How can you induce crystallization if the solution does not crystallize upon cooling?

scratch inside to make point for crystals to form

During the column chromatography, why is it important not to let the methanol level drop below the surface of the silica gel?

So silica doesn't dry out; affects column's ability to purify compound

If you don't know molar weight of compound, what analytical analysis would you use: GC or NMR?

NMR provide info on structure of a molecule, which can calculate molecular weight, but GC only separates compounds based on volatility (doesn't give molar mass info)