ochem II lab final
Which carboxylic acid is needed to make octyl formate?
Formic acid
Analytical method used to confirm the structure & functional groups of a product
IR spectroscopy
Wavelength or frequency: -increases as energy increases -measured in nm -measure of cycles per unit time
-frequency -wavelength -frequency
The area of a signal that corresponds to the number of nuclei at that frequency (NMR)
Integration
In the Williamson Ether Synthesis, a base deprotonates phenol. How should the moles of base compare to moles of phenol? why?
Moles of base = moles of phenol Too much base might result in the base acting as a nucleophile instead of phenolate Not enough base might mean not all phenol is deprotonated/won't react completely
Does NMR radiation break bonds?
No, it is low energy (long wavelength, low frequency) and high energy radiation is needed to break bonds
Can all molecules be analyzed using proton NMR?
No, only molecules with hydrogens
Xylene is an ideal solvent for Diels-Alder reactions, why?
-low freezing point -high boiling point -better solvent for reactants than product
Which alcohol is needed to make octyl formate?
Octanol
Sn2 occurs in ____ steps. Unsubstituted electrophiles react _______ than substituted electrophiles -- why?
One step. unsubstituted react faster than substituted, because of decreased crowding.
What are the possible products of an acid-catalyzed hydration of an alkene?
Primary, secondary, or tertiary alcohol
In NMR, shielding refers to ...
REDUCED impact of the applied magnetic field on a nucleus due to the presence of ELECTRONS around the nucleus
Technique used to separate pure product from any excess reagent, impurities, byproducts
Recrystallization
After a recrystallization, a pure substance should appear as large crystals, what should you do if it doesn't?
Reheat and allow the contents to cool more slowly
How to report melting point when doing a melting point determination?
Report as a range from when melting starts to when it ends
What is the visual indicator of a positive Tollens' test (which compound)
Silver metal
Nerolin is synthesized by an ____________ reaction
Sn2 -- Williamson ether synthesis
The appearance of multiple peaks for a single nucleus due to neighboring nuclei (NMR)
Splitting
___________ alcohols are more reactive toward dehydration -- why?
Tertiary and secondary -- increased stability of the carbocation intermediate
How to use the tare function on a balance
-place glassware on the balance -press tare/zero button to cancel out its mass -add sample, record its mass
What is the role of the acid catalyst in dehydration of an alcohol?
-protonates hydroxyl group -deprotonates adjacent carbon
What is the role of the acid catalyst in the rearrangement of pinacol?
-protonates hydroxyl group (water Lg) -conjugate base deprotonates an oxygen after rearrangement
Benefits of microscale chemistry -->
-reaction mixtures have volume less than 5ml -faster workups -reduced chemical waste
Why are organic models useful?
-rotations & conformations of a molecule -overall shape of a molecule -stereochemistry of chiral molecules -interpreting Newman projections -do not help compare bond lengths or atom sizes -do not help in determining Lewis structures
What is needed to run a spectrophotometry experiment?
-sample solutions -cuvette -spectrophotometer -blank solution do not need hot plate or stir bar
What to do when removing glassware from a kit?
-set out support like a cork ring or clamp to stop it from rolling -make sure the glassware is clean & free of cracks before using it
How to heat a solution to boiling on a hot plate
-start and stabilize the stir function -turn heat to medium -turn up the heat only if the solution is not boiling after 10min
Which items can be used to control boiling when heating liquid in a round bottom flask?
-stir bar & stir plate -boiling chips or stones
How to prepare a sample in a capillary tube for melting point determination
-tap tube into sample with open end of tube -tap until sample is a couple mm high -hit closed end on the table or into a longer tube to move thes ample down -make sure you can see the solid in the magnifier of the apparatus
To run a spectrophotometry experiment - ___________ the spectrophotometer - select the correct _____________ -run a measurement on the ____________ solution -then run measurements on ______________ solutions
-warm up -wavelength -blank -sample
Wavelength or frequency: -Measure of distance: -Measured in Hz -Increases as energy decreases:
-wavelength -frequency -wavelength
What to do when done using glassware from a kit?
-wipe it down to remove cleaning solvent -inspect for cleanliness/defects -put it back in its original position in the kit
What is the ideal molar ratio of borane (BH3) to alkene in hydroboration?
1 mol borane to 3 mol alkene
A balance with 0.01g tolerance would give a measurement with _______ digits after the decimal point
2 digits after the decimal point
Dehydration of a secondary alcohol occurs in ______ steps
2 steps protonation of OH, water Lg --> carbocation intermediate H removed, double bond formed (E1)
What is chromatography?
A technique to separate mixtures based on the molecular properties of the involved chemicals
Significant figures for add/subt vs mult/div
A/S -- same number of digits to the right of the decimal point M/D -- same number of SFs as the number in the problem with the smallest amount of those
Accuracy vs. precision
Accuracy -- experimental measurement close to the true value Precision -- how close repeated measurements using the same device are to each other
Why is it preferable to use an acid anhydride for ester synthesis instead of a carboxylic acid?
Acid anhydrides are less stable than esters, so the equilibrium favors the ester product
The goal of recrystallization is to form crystals, but you might form an oil instead. What should you do?
Add more recrystallization solvent, form a solution & cool again
(Aldehydes/ketones) can be oxidized, the other cannot -- why?
Aldehydes can, ketones cannot because aldehydes have a H next to the carbonyl, oxidation does not require breaking C-C bonds
Which PPE would help with this problem? -Solution spills down the front of the lab bench -Solution splashes up toward your face -Beaker slips out of your hand onto the floor -Unknown solution drips onto your hand
-Lab coat -Goggles -Closed-toe shoes -Gloves
How to end a reflux
-Lower the heat source, then turn off the heat -Leave the condenser water on until the system has cooled
How to report the most accurate melting point possible
-Quick heating to estimate -Slow heating, carefully observe melting -Slow heating, confirm careful measurement
What are the concerns presented by overheating a distillation to a dry flask?
-Remaining solid residue might contain explosive peroxides -Empty glassware might heat quickly, igniting vapors from the distillation
Determine the product: amine + carboxylic acid
Amide
Best position of the hood sash when working in a fume hood?
As low as possible, no more than halfway up
Washes vs extractions: Moves desired compound from one layer to another: Leaves impurities in their starting layer: Leaves compound in its starting layer:
Ex Ex Wash
Washes vs extractions: Often involves a reaction in one layer: Moves impurities from one layer to the other:
Ex Wash
Which part of an ester comes from the carboxylic acid, which part from the alcohol?
The OR group is from the alcohol (OR nucleophile attacks carbonyl!!), the R-C=O part is from the carboxylic acid (ethyl propanoate)
How does a Lucas test differentiate between alcohols?
The reaction involves a carbocation intermediate, so tertiary alcohols will react faster than primary
Which solvent should be used to wash the solid material collected from a filtration?
The same solvent as the liquid in the original mixture
Which hydrogens will be the furthest downfield?
Those close to electronegative atoms like oxygen, halogens
What is the purpose of a drying agent in the workup of an organic reaction?
To absorb small amounts of water
In a Diels-Alder procedure, a wet paper towel is used. What is its purpose?
To encourage condensation during reflux
The end of the NMR spectrum close to the reference signal
UPfield
How to heat a round bottom flask in a heating mantle? Plug the heating mantle into a ___________ Turn heat up _______________ Do not exceed _________ of the max output of the device
Variac or Powermite gradually 50-60% of max output
Which color has shortest wavelengths? Longest?
Violet - shortest Red - longest
When should you start timing the reflux, when there is a required length of time for it to occur?
When the reflux ring stabilizes in the condenser
Lucas's test shows the presence of _________ positive is ___________, negative is _________
alcohols positive -- insoluble oil negative -- colorless solution
Tollens' test reaction (aldehydes + silver ions) -- what is oxidized? what is reduced?
aldehyde is oxidized, silver is reduced
Tollens' test shows the presence of __________ Positive is_________ and negative is ______
aldehydes positive -- silver precipitate negative -- colorless solution
2,4-DNP test shows the presence of _______________ Positive is _____ and negative is ___________
aldehydes & ketones positive -- yellow precipitate negative -- orange solution, no precipitate
The ceric ammonium nitrate test (CAN) shows the presence of ___________ Positive is ___________, negative is ________
aliphatic alcohols positive -- color change to red negative -- yellow solution
R-MgX with water ---->
alkane! R group takes H+ from water
Determine the product: acyl chloride + amine
amide
Ball-and-stick model kits use ____________ connections for bonds, space-filling model kits use ______________ connections for bonds
ball-and-stick -- longer connections space-filling models -- shorter connections
Sn2 reaction -- Alcohol + alkyl halide Add ______ first to _______ the alcohol so it will attack the alkyl halide
base to deprotonate the alcohol
A Grignard reagent is a (acidic/basic) (nucleophile/electrophile)
basic nucleophile
Gamma rays and visible light are both ________________ but gamma rays have _________ than visible light
both electromagnetic radiation gamma rays have more energy than visible light
Which key feature is formed in a Grignard reaction?
carbon-carbon bond
1,2 diol + strong acid -->
carbonyl product, usually a ketone
Two molecules that combine to form an ester are ...
carboxylic acid + alcohol -- Fischer esterification!!!
Esters or carboxylic acids: reactions with base are known as neutralizations
carboxylic acids
The frequency at which a nucleus absorbs and resonates with a magnetic field (NMR)
chemical shift
Use a ___________ for stability when suspending a flask on a ring stand
clamp
Before using a flask, inspect it for __________________
cracks or imperfections
Diene should have a ____________ group, dienophile should have a ____________ for a successful Diels-Alder rxn
diene -- electron-donating group dienophile -- electron withdrawing
Pinacol Rearrangement: Which test is used to confirm that your reactant is a diol, and which is used to confirm that your product is a ketone?
diol --> Periodic acid test (white precipitate) ketone --> 2,4-DNP test (yellow precipitate)
The periodic acid test shows the presence of __________ Positive test is _____________ _______ and periodic acid are needed to complete the test
diols positive -- white precipitate Silver nitrate is needed
In general, alcohols ________ when mixed with water -- why?
dissolve OH bonds in alcohols can hydrogen bond with water
An aldehyde hydrogen will be (upfield/downfield)
downfield -- deshielded
Esters or carboxylic acids: are notable for their pleasant fragrances
esters
To prepare to work in a fume hood -- gather what you need (when?) Work in the _________ of the work surface (what part?) What to do when you have to step away for a min?
gather what you need in advance work in the middle of the work surface lower the sash if you have to step away
Connectors of a glassware kit should only be used to connect _______________________
glassware from the same kit
Handle a cuvette by the ________, don't touch the ________. _______ the cuvette before placing it in the spectrophotometer
handle by textured sides, don't touch smooth sides. wipe down before placing it
Which procedure cannot be done on a hot plate, only a Bunsen burner?
heating a crucible -- a crucible is ceramic, ceramic objects should not be heated on a hot plate
Black connectors in a microscale glassware kit should be used for _______________________
high boiling aromatics
The highest energy color in the visible spectrum is ____________, the lowest energy color is __________
highest - violet lowest - red
How to recognize reduced & oxidized organic molecules?
look at the structures -- more (reduction) or less (oxidation) CH bonds
The iodoform test shows the presence of ________ Positive is ________, negative is ___________
methyl ketones or alcohols w/ an alpha methyl group positive -- yellow precipitate negative -- colorless solution
To isolate a single variable when rearranging equations -->
move all variables to the other side by using the opposite function on both sides of the equation
When rearranging an equation to isolate a single variable, make sure that variable is in the (numerator/denominator)
numerator
Hydroboration of an alkene occurs in ___________ steps Boron is on the _________ carbon Oxidizing agent attacks __________ Major product ___________ follow Markovnikov's rule
one concerted step Boron on less-substituted carbon Oxidizing agent attacks boron, places an OH there Major product does NOT follow Mark's rule
A Grignard reagent is prepared when ____________ reacts with _________ in an ___________ solvent
organohalide + magnesium, ether solvent
Rearrangement of pinacol after water leaves -- cation originally on the carbon that _____________ but it is more stable on the carbon that ___________
originally on carbon that had the leaving group more stable on the carbon that has an OH group rearrangement shifts a substituent to form a more stable cation
Hydrogen peroxide is classified as an ___________ and can be _____________ Hydrogen peroxide can be __ if it decomposes too rapidly Dilute hydrogen peroxide is stable for about ________
oxidizer & corrosive decomposes too fast --> explosive (O2 gas produced) Dilute solution stable for about 1yr
A compound with an OH bonded to a benzene ring (no matter what else is on the benzene ring) is called _____________
phenol alcohol
Ferric chloride test shows the presence of _____________ Positive is ________, negative is _____________
phenols positive -- color change to purple negative -- colorless solution
Why do aldehydes & ketones have a higher boiling point than the corresponding hydrocarbons?
polarity of C=O bond creates dipole-dipole interactions, which are stronger than the London dispersion forces present in hydrocarbons
Why is a Grignard reagent more reactive than the starting organohalide?
polarity of R-Mg bond C pulls electron density toward itself C-Mg bond is weak
Shielding can be decreased by ... (NMR)
presence of more electronegative groups around the nucleus
The Jones' test (chromic acid test) shows the presence of _____________ positive is __________, negative is _________
primary or secondary alcohols positive -- color change to green negative -- orange solution
Markovnikov's rule says that the proton adds to the ________ carbon and the carbocation will be on the _________ carbon The nucleophile will end up on the _____ carbon
proton --> less-substituted carbon carbocation ---> more-substituted carbon, more substituents stabilize it ^^ nucleophile adds here
Esters have ____________ intramolecular forces compared to acids or alcohols of similar size -- why? Esters are ________ volatile than acids and alcohols
reduced forces -- because of the lack of hydrogen bonding. Esters are MORE volatile
The glass panel in front of the fume hood that shields you from fumes is the __________________
sash
What type of alcohols will undergo a more effective dehydration reaction?
secondary or tertiary, because of the cation intermediate
A shielded nucleus is further ___________________ and a deshielded nucleus is further ______________ (NMR)
shielded nucleus -- upfield deshielded nucleus -- downfield
The pinacol rearrangement shifts ____________ to form _____________
shifts a substituent from one carbon to another to form a more stable cation
Highest energy = _____________ wavelengths
short wavelengths, high frequency
Sn2 -- _________________ reaction where Nu attacks E _______________ leaving group leaves. Rate of rxn depends on concentration of ______
substitution reaction Nu attacks E at same time as Lg leaves Rate depends on concentration of both reactants
What is meant by the term bumping?
sudden & uncontrolled boiling of liquid
The most common acid catalysts used for alcohol dehydration are ...
sulfuric or phosphoric HCl or HBr not used, the Br- or Cl- ions could compete in the Sn2 reaction as a nucleophile
You can tell if an alcohol is primary, secondary, tertiary based on ...
the number of carbons attached to the OH-bearing carbon
The product of the Diels-Alder reaction of anthracene & maleic anhydride has __________________
two separate aromatic rings -- more aromatic pi electrons
Substances that evaporate readily & produce large amounts of vapors are __________________
volatile
The horizontal flat area of a fume hood where you do your experiments is __________________
work surface
Esters or carboxylic acids: form hydrogen bonds amongst themselves & have lower vapor pressure
Carboxylic acids
Esters or carboxylic acids: usually have a sour odor
Carboxylic acids
What are the best practices for safely handling waste in the lab?
Check labels or instructions before disposal, always wear PPE
Why does the pinacol rearrangement use H2SO4 instead of HCl as an acid catalyst?
Cl ion could result in a competing substitution rxn
What if a balance has persistent fluctuations in mass?
Contact the TA/instructor to adjust it
Why is HCl used in the Grignard procedure?
Convert benzoate salt into benzoic acid (HCl is a source of protons)
The end of the NMR spectrum farthest from the reference signal
DOWNfield
How is scientific notation formatted?
Decimal x 10^ Decimal can be 4.5, 4.55, 0.045 etc
How to determine how many signals in a proton NMR spectrum for a compound?
Equivalent hydrogens -- how many "types" of hydrogens = how many signals
Determine the product: acid anhydride + alcohol
Ester
Determine the product: alcohol + carboxylic acid
Ester
Esters or carboxylic acids: don't form hydrogen bonds amongst themselves & have higher vapor pressure
Esters
Esters or carboxylic acids: reactions with base are known as saponifications
Esters
How should you determine the last digit in a measured number?
Estimate one digit past the smallest precisely known digit/marking on the ruler
In a Grignard reagent, which atom has a partial positive and which has a partial negative?
Mg-X is positive, carbon is negative
What are the necessary parts of a Grignard reagent?
(Alkyl group) + Magnesium + (halogen) phenylmagnesium chloride ethylmagnesium bromide isopropylmagnesium chloride NOT methylcalcium bromide (Ca not Mg)
If you are performing a recrystallization, what should you do if the crystal growth does not start on its own after the solution reaches room temperature?
-Add a bit of solid as a seed crystal -Scratch the bottom of the flask gently with a stirring rod
Best practices for adding boron reagent to the alkene in a hydroboration oxidation reaction?
-Add boron reagent slowly -Use a thoroughly dry syringe & glassware
What are best practices for sharing a lab balance w/other students
-Alert TA or instructor about issues -Brush off chemical dust around the balance -Only tare glassware when you are about to use it
Why is concentrated H2SO4 used for dehydration of an alcohol, instead of dilute HCl?
-Cl ion could result in a competing substitution reaction -additional water solvent from the dilute solvent could reverse the dehydration
How to remove a round bottom flask from an oil bath?
-Heat resistant gloves -Raise the clamp to lift the flask out of the oil bath -Allow the flask to cool -Use a paper towel to remove oil from the bottom of the flask
How to stabilize a boiling beaker on a hot plate
-Turn down stirring speed -Make sure beaker is in the center of the plate
In a modeling kit, how do the balls representing atoms of distinct elements differ?
-arrangement of holes -number of holes
What to do before heating glassware on a hot plate?
-check the glassware for cracks -make sure the glassware is designed to be heated -make sure the hot plate has no frayed cords
What are the changes you'd see in the IR spectrum of pinacol & its rearranged product?
-disappearance of CO single bond band -disappearance of OH band -addition of C=O band
What would you see on an IR spectrum of the product of an alcohol dehydration?
-disappearance of OH band -disappearance of C-O band -addition of C=C double bond band
How to increase yield of product in a reversible dehydration reaction?
-distill off the product during the reaction -- this will reduce the reverse reaction (hydration is the reverse of dehydration)
What's the best safety approach when working with an unknown substance?
Assume it is hazardous, always wear appropriate PPE
Where should the tip of the thermometer be placed in a microscale distillation?
At or slightly below the side arm for the distillation head
Ball-and-stick model kits focus on ____________________, space-filling models focus on ______________
B/S -- properties of bonds SF -- molecule's overall shape
The empirical formula CH2 really represents ...
C(X) H(2x) so C2H4, C3H6, etc
What are common solvents used for NMR samples?
CDCl3, C6D12, C6D6, CD3OD, CD3CD2OD common solvents but with D instead of H
Why is KOH preferred over NaOH in organic reactions?
KOH is more soluble in organic alcohols
Deshielded hydrogens have ____________ electronegative groups nearby
MORE -- electronegative groups decrease shielding
Why does the reaction of anthracene & maleic anhydride need to be kept away from water?
Maleic anhydride can react with water, opening the ring
Quick, numeric analysis to characterize a product & assess its purity
Melting point
When working in the fume hood, how to minimize clutter
Only keep items in there that are being used for the current experiment, do not store chemicals in the fume hood
Which step in the Grignard Reaction is made easier through the application of ultrasonic waves?
Preparation of the Grignard reagent
Which alcohols are the easiest to oxidize, and which are the most reactive toward a reaction involving the -OH acting as a leaving group?
Primary alcohols are easiest to oxidize (multiple CH bonds available by the hydroxyl group) Tertiary alcohols are most reactive toward -OH leaving group (3 C-C bonds increase stability)
How can you recognize the catalyst in a mechanism?
The catalyst is used & then regenerated in a later step
After a recrystallization, a pure substance should appear as ...
a network of large crystals
When a reaction is properly refluxing, where should you see vapors from the heated mixture?
about 1/3 up the condenser height
The front vent of a fume hood which helps maintain proper air circulation is the __________________
airfoil