O Chem 3105 Lab Final
What are the two most common adsorbants used in column chromatography?
Silica gel and alumina
Electrons in which type of bond are excited by radiation during this experiment?
The pi bond
What feature of TLC makes it useful for monitoring reactions?
The speed of the technique
Wall coated (WCOT) columns are not packed; the liquid phase is applied directly on the walls of the columns. This is the type of column used in the GC for our organic chemistry labs. This type of column can only be used in what type of separation?
Analytical GC separation
What conformation is preferred for E2 elimination to occur?
Anti-periplanar
When should you remove the rubber tubing from the filter flask?
BEFORE turning the water off
Which of the below methods will allow water insoluble organic acid to become soluble?
make water basic with an aqueous sodium hydroxide solution. Happens because of increased H bonding from OH-.
Conjugation
Lower carbonyl frequency
Hydrogen bonding
Lower carbonyl frequency
What is the number of moles in 5.00 mL of a 0.10 M solution?
0.00050 mol
Calculate the number of milliliters needed to give 2.5 mmol of the alcohol shown below.
0.37 mL
Calculate the number of grams needed to give 2.5 mmol of the alcohol shown below.
0.46 g
How much unknown sample will you use?
0.50g
The photoisomerization of cis-Rhodopsin in the retina is extremely sensitive, how many photons are required for the photoisomerization reaction?
1
One mole of t-butyl chloride will produce one mole of HCl. One mole of HCl can neutralize one mole of NaOH. Fill in the blank below with the amount (mL) of 0.10 M NaOH needed to be added to the reaction mixture to observe 20% completion when using 5.00 mL of of 0.10 M t-BuCl. (Remember significant digits)
1.0
The equation to calculate the number of theoretical plates in a column is given in your prior reading section and below. Calculate the number of theoretical plates (n) for an analyte in a column that appears at 3.5 minutes (retention time) and has a baseline width of 20 s.
1764 theoretical plates
The equation to calculate relative retention time is r= Ta/Ts. Calculate the relative retention time (r) of the analyte with respect to air/solvent(s) if the air or solvent peak(s) (ts) appear at 15 s retention time, and the analyte peak (ta) appears at 4.50 min.
18
Extractions are used to separate two substances. What percent of Substance A contains a mixture if you start with 1.0 g Substance A & B and isolate 0.25 g of Substance A after extraction?
25%
How many points are deducted per business day for late lab reports?
3 points
Determine the percent yield for the following generic reaction using the information given below: Compound A → Product P You start with 11.0 mL of Compound A and obtain 11.0 mL of Product P. MW of Compound A: 220 g/mol; Density of Compound A: 2.20 g/mL MW of Product P: 110 g/mol; Density of Product P: 0.75 g/mL
68%
You start with 1.00 g of crude product and isolate 0.75 g of pure product after recrystallization. What is the percent recovery
75%
You will start this experiment with 25 mg of the trans isomer. What is the percent yield if you obtain 20 mg of the cis isomer?
80%
The qualitative bromination test for the presence of unsaturation is actually a stereospecific reaction. Which of the follwoing is/are the sterospecific products of this?
???
Which component in the mixture is the more volatile? (lower BP)
Methanol
When adding NaOH. You should check that the aqueous layer is basic. The question is, should you add the entire 40 mL in one portion, or add smaller portions (~5 - 10 mL) and check the basicity between these smaller portions. (Hint - working with a minimal amount of solvents and solutions is best)
Add small amounts and check basicity between each addition. Stop adding NaOH when aqueous phase is basic. LOOK AT THE ELO's
A compound's IR spectrum shows a very intense peak between 3500-3200 cm-1 (see the red peak in the IR spectrum below). What functional group would you expect is present in the compound?
Alcohol
GC separations and distillations (which are separations as well) are similar in that the increase of theoretical plates increases resolution (separation). A theoretical plate is _______________________.
An evaporation-condensation cycle
The gas chromatography instrument used in the organic chemistry instructional laboratories injects a very small sample (0.05 - 0.10 µL) of a dilute solution into the instrument. What type of separation is this?
Analytical GC Separation
Bromophenol blue changes from ______________ to ______________ when the HCl produced in the reaction below neutralizes the known amount of NaOH that was added to the reaction mixture.
Blue to yellow
What is the rate of reaction?
C and D...The rate at which a reactant is consumed as a function of time The rate at which a product is formed as a function of time.
Which intermediate is formed in E1 reaction?
Carbocation
After a sample is analyzed, the GC software will produce a plot/graph that you can analyze. You can see the sample component peaks as well as a peak for the solvent used to dilute your sample. This plot/graph is called a _______________________.
Chromatogram
Determine which compound is the limiting reagent in the following generic reactio: Compound A + Compound B --> Compound C if you start with 0.15 g of A and 0.30 of B. MW of Compound A - 100 g/mol MW of Compound B - 300 g/mol
Compound B
Answer the following question based on your knowledge of factors that affect carbonyl frequencies (you read about these in Experiment 5's prior reading, p 295-297). Which statement best describes the trend in carbonyl absorption frequencies of the aldehydes shown?
Conjugation lowers carbonyl frequency. The conjugated (E)-but-2-enal has a lower carbonyl frequency at 1699 cm than butryaldehyde.
What type of automatic pipet can be set by the user to deliver any volume within a range of the pipet?
Continuously adjustable
Look at experiment 8
DO IT
You have performed TLC analyses in previous labs and will perfrom column chromatography in this experiment. In column chromatography, the mobile phase_____________ the column; in TLC, mobile phase_____________ the plate.
Descends; ascends
What are the cis and trans isomers of an alkene system called?
Diastereomers
Which is the only solvent that should ever come in contact with an IR salt plate in the organic chemistry teaching labs?
Dichloromethane
Which of the following is NOT one of the essential steps of crystallization?
Dissolve the material in a maximum amount of warm solvent
How do you calculate the Rf value?
Distance traveled by the substance divided by the distance traveled by the solvent.
Which of the following are differences between E1 and E2 in terms of reaction mechanisms?
E1 reactions frequently undergo rearrangements E2 reactions are concerted reactions with no intermediate E1 reactions for a carbocation intermediate and a not concerted
Reactions like those described in Experiment 11 are called elimination reactions because a small molecule is _______________________ from the organic molecule. When that small molecule is water, the reaction can also be called _______________________.
Eliminated, dehydration
During the solvent extraction experiment, which layer is hydrocarbon in?
Ether layer
Documentation for an absence can be submitted 8 days after missed lab.
False
In today's reaction, TEMPO is used as a stoichiometric oxidant.
False
The injection temperature causes vaporization. True or false: 400 °C is a good injection temperature for a sample that decomposes at 350 °C.
False
The trans isomer of 1,2-dibenzoylethylene is less stable than the cis isomer
False
You should always heat a distillation flask to dryness
False
Which is not a good choice for weighing solids?
Filter paper
_______________________ is very sensitive; it can detect material of amounts less than a microgram.
Flame-ionization detector
Increasing the surface area in contact with the vapor phase can increase theoretical plates in the distillation column. This technique is called _________.
Fractional Distillation
Sublimation occurs when a substance goes directly from the solid phase to the ______________ phase
Gas
When working with acids and bases what PPE should be used to protect yourself?
Gloves, goggles, lab coat
Benefits of using drying agent sucha as magnesium sulfate?
High Surface Area Increased rate of drying
In the presence of water, aldehydes exist in equilibrium with their _________
Hydrates; ELO's dude...c'mon
An extraction solvent should be __________________ the solution solvent.
Immiscible with
More substituted carbocation is most stable.
It is more stable because of hyperconjugation
What conclusion can you make if it takes 20 s for bromophenol blue to change colors in the following scenario? You have a mixture that contains 0.50 mL of 0.10 M NaOH, 4.50 mL of water, and 5.00 mL of 0.10 M t-butyl chloride.
It took 20 s for 10% of the t-butyl chloride to react
Where is the bulb of the thermometer positioned in the distillation apparatus?
Just below the opening to the condenser.
Zaitsev rule sayas that a reaction will proceed in the direction that yields the most highly substituted alkene.
Just know about alkene substitution
What is best way to know contents in any given flask?
Label the flask
The automatic pipet should never be ___________ and always returned ___________
Laid flat or inverted, to the pipet stand in an upright position.
Why are methyl and primary ethers preferable products for Williamson synthesis of ethers?
Methyl and primary halides are more amenable to to the SN2 Secondary and tertiary halides could undergo an elmination reaction
Which of the following is a safety concern when heating organic solvents to saturate a solution?
Most organic solvents are extremely flammable and most organic solvents produce very toxic vapor.
What is the term used to describe the solution that is separated from crystals in crystallization or recrystallization?
Mother liquor
If a sample does not have sufficient vapor pressure to be soluble in a carrier gas, will you be able to use GC as an analytical technique?
No
Should you ever leave a MelTemp unattended when heating?
No
Where should waste go?
Non halogenated waste
Acid catalyzed reactions with alcohols are fastest on tertiary carbons.
Order of reaction rate 3.2.1
The process of converting an alcohol to a ketone or an aldehyde is called __________.
Oxidation
What should you use to mark your TLC plate?
Pencil
Different stationary phase materials have different binding properties, which stationary phase material would be useful to help elute two unknowns based on their polarity?
Polyethylene glycol (Carbowax)
You use an aldehyde to get a _______________ alcohol.
Primary
Match the safety hazards
Propyl Iodide- Cancer suspect agent Sodium hydroxide- Strong base, can burn skin and eyes Concentrated Acids- Strong acids, can burn skin and eyes
Decrease in C-CO-C internal bond angle
Raise carbonyl frequency
Substitution with electronegative atoms
Raise carbonyl frequency
You measured the Rf of various compounds on the TLC plates in Experiment 5. What does Rf stand for?
Retention factor
A molecule that is strongly adsorbed on the stationary phase of a column will move _________ down the column.
Slowly
Brewing tea in aqueous sodium carbonate solution and then separating the water away from the tea leaves is an example of what kind of extraction?
Solid-liquid extraction
If there is no suitable single solvent available for recrystallization, you can use...
Solvent pair
Structure of caffeine
Structure B...look it up
Match the factors listed with how they affect the carbonyl (C=O) frequency.
Substitution with electronegative atoms A. Raise carbonyl frequency Decrease in C-CO-C internal bond angle A. Raise carbonyl frequency Conjugation B. Lower carbonyl frequency Hydrogen bonding B. Lower carbonyl frequency
Why does TLC not scale up very well when using it to separate compounds?
TLC can only be used with very small quantities of material, usually 2-20 micrograms
What combination of compounds do you expect to be present in the aqueous solution after brewing the tea leaves?
Tannic acids, caffeine, sodium carbonate
You will use either sodium methoxide or potassium tert-butoxide as base in this experiment. Potassium tert-butoxide is a "bulky" base. What does it mean to be a "bulky" base?
The base is relatively large, or bulky. It is actually so big that it can only abstract an internal β-hydrogen and will usually produce an anti-Zaitsev product
What are some differences expected to be seen when comparing the IR spectra of the trans starting material to the cis photoproduct? Vamsi sucks btw
The cis isomer will display a cis, in-phase out-of-plane bend at 820 cm The trans double bond will appear as a single medium intensity band at 970 cm
Why are phenols typically stronger acids than simple alcohols?
The conjugate base of a phenol is stabilized by resonance delocalization.
In addition to obtaining an IR spectrum, you will use bromination as a qualitative test for the presence of unsaturation (a double bond, in this case), see the reaction below. What is the change you will observe in the reaction solution?
The deep orange color of bromine will disappear
What is one of the factors for group frequency molecular vibration in infrared spectroscopy?
The group must have a dipole moment change
Which layer will the bottom layer in the liquid-liquid extraction performed in this experiment?
The organic layer (methylene chloride)
Why is the phase transfer catalyst soluble in the organic layer?
The large organic groups attach to the catalyst.
Which is most stable alkene?
The most substituted trans compound
What is distillation?
The process of heating a liquid to boiling point, condensing the heated vapor by cooling and returning either a portion, or none of, the condensed vapor to the distillation vessel.
Why does the endothermic photoisomerization of transs-1,2-Dibenzoylethylene to the cis isomer only proceed in the forward direction?
The reaction conditions are under visible radiation and the cis isomer only absorbs ultraviolet radiation
Why is the SN1 reaction referred to as solvolysis?
The solvent is on of the reactants
The solubility of a sample in a carrier gas depends mostly on what?
The vapor pressure of the substance(s) in the sample
What is the purpose of NaOH in this experiment?
To help measure the rate of reaction; LOOK AT THE ELO's
Phosphoric acid is used as a protonating acid in the reaction below. Why is it important to protonate the starting alcohol?
To produce a good leaving group, water Without the protonation step, the hydroxide ion, a oor leaving group, is the only available leaving group.
Methanol is flammable
True
Concentration of the TLC sample is very important. For liquid compounds (like benzyl alcohol), just __________________ the compound then a few drops of solvent. For solid compounds (like benzoic acid), just __________________ the compound and dissolve it in the solvent.
Use 1 drop of; cover the tip of your spatula with
What should you do if you create an emulsion when doing the liquid-liquid extraction?
Use a centrifuge to break the emulsion/Vamsi Sucks
When the provitamin, 7-dehydrochloesterol, is exposed to sunlight, it photoisomerizes to what compound?
Vitamin D3
Does adding brine (NaCl) help dry ether?
Yes
Which of the following statements is correct?
You must obtain the carbonyl IR frequency data for all products made in your lab section.
Process of evaporation and condensation is achieved by the theoretical construct known as...
a theoretical plate
Match the letter with the correct column component, one will be used twice
a. elution solvent b. sand c. Stationary phase d. sand e. cotton
The natural product being isolated in this experiment is a white crystalline____________
alkaloid
How much sample should be added to the melting point capillary?
approximately 1 mg, about 2 mm in height once added to the capillary
Which arrow shows where clamp should be on distillation flask?
clamp neck of flask to thermometer adapter (arrow C)
In today's reaction, you will be distilling your product away from the reaction mixture. You must ensure that the distilling vapor does not go about 102 degrees Celcius. The boiling point of cyclohexanol is:
greater than 102 degrees Celcius
In liquid-liquid extractions, the extraction solvent should be __________________ the solution solvent
immiscible with
Biphenyl has a known melting point of 68-70 °C. You measure the melting point of Unknown X to be 68-70 °C. The Biphenyl-Unknown X mixture melts at 60-66 °C. Unknown X _________________ Biphenyl.
is not
Fractional Distillation is used to separate two liquids that have boiling points that differ by ________ 30-40 degrees Celcius.
less than
You have now performed a solvent extraction and a recrystallization in the labs. The solvents used in recrystallizations should be ______________ and solvents used in extractions should be ______________. Vamsi sucks, Nick rules
miscible, immiscible
Where is the water inlet on the Distillation apparatus?
next to distillation flask on condenser. (arrow B)
You should start timing the reaction after adding what compound to the solvent?
t-butyl chloride
In chemistry, the term "wet" means:
the material in question contains water
You will perform the reaction shown below in this experiment and you should obtain a mixture of the products shown. You will submit samples of your product mixture to be analyzed by gas chromatography. From what you know about Zaitsev elimination products and alkene stability, identify which of the products is the most stable. Would the most stable product be the major product or the minor product?
trans-2-Heptene is the most stable product; it would be the major product if M+ -OR is a small base ELOS
According to the lab manual, the first step in any filtration is:
wet the filter paper with the solvent being used
