Ochem Lab Final

What are examples of catalysts?

- KOH in synthesis of tetracyclone - H2SO4 in the Fisher esterification

You make a mistake and only count 30 min from the time yo started heating, not from the time reflux had started. Which of the following could be a consequence of that mistake?

- May have a reduced yield - reaction may not go to completion

Construction of your column

- a top layer of sand - a bottom layer of sand - a short plug of cotton - a layer of silica gel

Equilibrium of the silica gel column...

- prevents exotherms - must be done befire loading the sample micture onto the column - removes air bubbles and cracks from the silica gel layer - is essential for good separation

What precautions must you take in term sof temperature when planning a Diels Alder reaction?

- temperature must be sifficient to overcome the activation energy of reaction - temperature must be low enough to not favor the reverse reaction

What techniques can be used to modify the position of the equilibrium by removing or sequestering a product?

- using a Dean-Stark trap and toluene azeotrope - formation of a solid preciptate - use of a drying agent to remove water

What techniques could you use to obtain solid sample of the 3 components of excedrin?

- you could apply vacuum to evaporate the eluent - you could use your hotplate to evaporate the solvent

In order to run a successful recrystallization...

- your desired compound must be solid - your desired compound must be soluble in a specific solvent at high temperature, and insoluble at low temperature

When evaluating an eluent for use in a column by TLC, the Rf of your desired compound should be...

0.3-0.5

Assuming 1.0 equivalent of benzoin, what is the minimum equovalent of Bismuth III nitrate pentahydrate that you can use to theoreitaclly have the reaction go to completion?

0.33 - nitrate ions re active species, since there are 3 ions the reagent can react 3 times before it is consumed

When doing a gradient elution you start your column with a ________ eluent mixture and progressively ___________ polarity until your target eluent mixture is reached.

1- nonpolar 2- increase

The melting point of the recrystallized product should be a ______ and a ______ compared to the melting point of the crude product

1. higher temperature 2. narrower range

According to Le-Chatellier's principles, which are ways to manipulate equilbrium?

1. increase the proportion of one of the reagents 2. remove or sequester one of the products

A more polar eluent will_______, while a more polar molecule will ________

1. shift spots upward 2. interact more with the silica and not move up as high

Which are vibrational modes of molecules?

6: bending, twisting, symmetric stretching, rocking, asymmetric stretching, wagging

I have a mixture of 3 compounds: A is acidic, B is basic, and N is nonacidic. If i treat my mixture with aqueous NaOH, which compound will remain the organic phase?

B (basic compound), N (neutral compound)

The spotting line of my TLC eluent can be submerged in the eluent, it wll not affect the results of my TLC?

False

True/False: Aqueous extraction is a suitable prurification method for the Diels Alder reaction?

False

True/False: Melting point should b recorded as an exact temperature?

False

True/False: You can use normal chloroform (CHCL3) as the solvent for your NMR sample

False- have to use deuterated chloroform to mask the H of CHCl3

True/False: FTIR can visualize ALL covalent bond vibrations

False= FTIR requires bonds to have a dipole moment in order to be visible

Methanol, diethyl ether, hexane, ethyl acetate: most polar and least polar

Most polar- methanol Least polar- hexane

You find in the lab two liquid samples with their labels erased! You know one is an aldehyde and one is a ketone. Which of the techniques that you used in the Compound ID lab would be the most accurate in helping you figure out which sample is which? (between melting point, NMR, and IR)

NMR

Unit of Rf

Rf has no unit

What is tmep of rough mp ramp rate? What is temp of precise mp rate?

Rough- 10ºC/min Precise- 1ºC/min

True/False: TLC is able to separate diastereomers of the same compound. If you had started with a 50/50 mixture of cis and trans cinnamic acid, you would have seen two spots in your cinnamic acid standard lane

True

True?False: Precipitates can be mixtures, while crystals are pure compounds

True

What makes a molecule more polar?

a greater difference in electronegativity

NMR spectrometer contain...

a magnet

Ethyl acetate organic phase would be

above the the aqueous layer- has a density of 0.902g/ml, and will sit above the water of aqueous layer

When you are done with your IR, you should clean your plates with _____ and kimwipes

acetone

I don't know which of my layers is water and which is my organic phase, and I've forgotten what solvent I used! What observation would you see that shows that the top phase is my organic phase?

adding a few drops of water to the top of my separatory funnel. The droplets pass through the top phase without mixing, then mix with the bottom phase. - water passing through the top phase and mixing with the bottom phase is an observation that tells you that your op phase is organic

A flash column is faster than a normal gravity column thanks to the application of

air pressure- flash columns use applied air pressure to accelerate the rate at which the eluent flows through a clumn

Which of these functional groups would be most deshielded (high ppm value) -CH2CL - aldehyde - alkene - benzene ring

aldehyde

Organic bases generally contain which functional group?

amine- generally nitrogen containing compounds

What fluoresces bright blue in TLC

anthracene

What can affect a 1H nucelus chemical shift in ppm

aromatic rings, resonance structures, electronegative atoms

Chloroform organic phase would

be below the aqueous layer

You have a solid sample you are using for melting point measurement. Your solid should...

be dry, reach 2-3 mm up the capillary

What was the oxidant in the synthesis of benzil lab

bismuth (III) nitrate pentahydrate

distillation is a method of separation based on...

boiling point

Why would column chromatography be more efficient at seperating out caffeine than the acid-base extraction?

caffeine is more soluble in aqueous solution so using column chromatography does not use aqueous solutions to separate compounds

What is most polar: acetaminophen, caffeine, aspirin

caffeine is most polar and will elute out first

Flash column chromatography is apecial type of column chromatography that uses__ to increase efficiency

compressed gas

How do you extract a compound and transfer it into an aqueuous phase if they are acidic functional groups?

deprotonate it- especially if acidic - phenols are acidic functional groups

Protonated/Deprotonated: Salicylic acid in a solution of pH 4

deprotonated

Protonated/Deprotonated: aniline in a solution of pH 12

deprotonated

As opposed to a TLC, the eluent moves _____ in a column.

downwards

What is an acid

electron acceptor (usually things that are positive)

What is a base

electrons donor

True/False: A catalyst gets consumed in a reaction

false

True/False: All isotypes of hydrogen atoms are visible in hydrogen NMR spectra

false

True/False: It's not necessary to cover/cap your TLC jar?

false

True/False: in a condensor, the water and reaction mixture are in physical contact and can mix

false

True/False: The C-O bond vibration in isopropanol is a broad peak around 3300cm-1

false- C-O bons are usually in the fingerprint region

True/False: Each time you add eluent, you should elute the solvent completely out of the silica gel so it becomes dry again before adding more eluent

false- never let gel dry

Which is less polar- hexanes or ethyl acetate?

hexane- more hexane over ethyl acetate= less polar

A TLC of my product gives a Rf of 0.37 using a 5:3 hexanes/ethyl acetate eluent. What would happen to the Rf if the eluent was changed to 3:1 hexanes/ethyl acetate?

it would increase (spot not travel as high)

Water in your sample would show as

large, broad peak at 3500 cm-1

What should be the solvent used to equilibrate your column?

least polar eluent ~ hexanes

Melting point range of impure compound will be

lower and broader

Rf value equation

middle of spot traveled/ solvent front

In TLC, the eluent is the ______ phase

mobile

Melting point of purer compound should be...

narrower and higher

Entropy is a measure of disorder. In the Diels Alder reaction you performed, do you expect the entropy to be positive or negative?

negative - more disorder= positive, less disorder = negative

Column Chromotography using silica gel separates compounds by...

polarity

How do you extract a compound and transfer it into an aqueous phase if they are basic functional groups?

protonate it - pyridines are basic functional groups

Protonated/Deprotonated: acetic acid in solution of pH 2

protonated

Protonated/Deprotonated: piperidine in solution of pH 7

protonated

What influences melting point?

purity of the sample

When using a UV lamp to visualize TLC spots, what should you see?

should observe dark spots on a fluorescent background

______ distillation is used to separate compounds with boiling points differing by over 100º C

simple

The leading edge of the solvent as it advances up your TLC...

solvent front

Fractional distillation requires the use of a fractioning column with increased_____ which allows for more vaporization/condensation

surface area

Where do more polar compounds show up on a TLC?

the bottom of the TLC plate

What does more hexanes mean?

the eluent is less polar

Using regular silica gel TLC's...

the more polar compounds will move less high than the less polar compounds

Reflux is observed when

the solvent drips steadily back into the reaction

One vaporization/condensation cycle corresponds to a...

theoretical plate

True/False: in a flash chromatography, the silica gel is stationary phase and the eluent is the mobile phase

true

True/False: when at reflux, the temp inside the reaction flask is constant

true

True/ false: the salt plates used in this experiment do not absorb IR radiation

true- plates are made of sodium chloride and thus do not contain any covalent bonds

What is correct when using a seperatory funnel for aqueous extraction?

vent regularly, point funnel towards the back of hood when venting, remove the stopper before turning the stopcock to pour out the solution, rest the funnel on ring stand

FTIR observes what kind of molecular motion?

vibrations

FTIR spectra are given in what units?

wavenumbers (cm-1)