Chem 242 Final

Why is LiAlH4 NOT a good reagant for the camphor reduction (as compared to NaBH4)?

Too reactive, would react with methanol and decomposed

Why did we not need a reflux condenser for the camphor reduction?

The reaction was too fast for the methanol/solvent to evaporate

Was the camphor reduction under kinetic or thermodynamic control?

Kinetic control—irreversible rxn, reduced activation energy for isoborneol formation (hydride reactions are irreversible)

Which isomer was the major product in the camphor reduction, isoborneol or borneol!

Isoborneol! Less steric hindrance to attack ketone from the bottom of the ring

In step 2 of the three step synthesis when forming tetraphenylcyclopentadienone, why does the reaction not stop at an aldol addition without the final condensation step?

Dehydration is spontaneous because it leads to a fully conjugated final product

Why is the reaction of enone B faster than the reaction of benzil?

Intramolecular reactions are more favorable than intermolecular

why can benzyne be spontaneously made from anthralinic acid despite its huge ring strain?

its formation leads to the release of small stable molecules like co2 and n2

why did we use a drying tube in the esterification rxn?

water would have pushed the reaction to the left (reactants vs products) and lowered yield

why is WebMO less accurate for NH and OH chemical shifts compared to CH chemical shifts?

doesn’t consider hydrogen bonding!

why is it only valid to compute energy values for isomers or balanced chemical equations?

you need to compare molecules with the same baseline

how do solubility tests in NaOH and NaHCO3 differ and why did we do both?

Weak bases like NaHCO3 will deprotonate C.A.s so they’ll be soluble, but phenols are only soluble in strong bases like NaOH

why are benzylic alcohols more prone to false positives with Tollens reagant than other alcohols?

They’re easier to oxidize than standard alcohols so would also reduce silver

which core functional groups give a positive result for the chromic acid test? (we didn’t run this one, but hypothetically)

aldehydes and alcohols bc they can be oxidized

why might a derivative table entry be blank?

unfavorable rxn/derivative is highly unstable, derivative is liquid

how do you calculate degrees of unsaturation?

(2C+2+N-H-X)/2, oxygen doesn’t matter

how to see if there are Br or Cl in compound?

n+2 peak! Br 1:1 ratio, Cl 3:1 ratio

how to determine # of carbon atoms in molecule based on mass spec?

(c13/c12)= % heavy atoms then divide that percentage by 1.1 %

why would water have NOT been a good choice of solvent in the camphor reduction?

The reactants aren’t soluble in h20, and water would compose NaBh4 too rapidly

for the esterification rxn/rxns in general, what was the purpose of using a reflux condenser instead of just heating the rxn in an open flask?

to make sure that the solvent doesn’t fully evaporate during the rxn time

why would running the esterification rxn for longer not result in a higher yield?

bc equilibrium would have been already reached and the concentrations of products vs. reactants wouldn’t change

why is using Cu as a catalyst in the three step synthesis greener?

Because then we’re not using Chromium or Manganese, both of which are really toxic!

why dissolve KOH in ethanol the day before using it for the 3 step synthesis?

bc it’s sluggish to dissolve and takes forever LMAO

why don’t we have to worry about 2 molecules of benzil doing an aldol condensation together?

they don’t have any alpha hydrogens to be deprotonated

why was there a significant change in color when tetraphenylcyclopentadienone was produced from benzil and diphenylacetone?

the product had a different level of conjugation compared to the reactants

is benzyne aromatic, antiaromatic, or nonaromatic?

aromatic! only one pi bond in the alkyne contributes to the aromaticity, so it has 6 pi electrons in conjugation

what is the primary hazard in step three of the three step synthesis?

isopentyl nitrite, a vasodilator!

why did many of the derivatives contain nitrobenzene groups?

they make the compound more likely to form crystals!

why might an NMR give noisy bad results?

too dilute solution, not enough volume solvent, solution not mixed well

what causes a color change in cerium test with phenols and alcohols?

cerium forming a complex with oxygen

how to distinguish between primary arylamines and secondary arylamines?

primary will form diazonium ions and release n2 gas while secondary amines will stop reacting at the yellow nitroso compound bc they don’t have another h to react

why is the oxime test positive for aldehydes and ketones but negative for esters and C.A.s?

aldehydes and ketones do addition reactions with amines to form imines, but esters/C.A.s do substitutions with amines to form amides.

how would the molecular ion region change if a compound had 2 Br atoms instead of 1?

1:2:1 ratio of M, M+2, and M+4 peaks

how are isoborneol and borneol related to each other?

diastereomers!

why did we do an extraction in the esterification rxn given that extraction wouldn’t separate the reactan alcohol and product ester?

it separates out the other reagants like acetic acid!

why doesn’t the cerium test require fully soluble reactants?

it’s a color change test, which can happen with only partial solubility

why are the two parts of the ferric chloride test (without hydroxylamine and then with) necessary?

the first part can identify phenols, the second part can identify esters that form enols with the addition of hydroxylamine that then coordinates with the FeCl3

what compounds will be soluble in water?

small compounds with less than 4 carbons, ions

which compounds will be soluble in hcl?

amines

the cerium test identifies?

alcohols and phenols

the ferric test identifies?

phenols and ester (color change!)

tollens test identifies?

aldehydes! (aldehyde gets oxidized, reduces silver complex to silver metal)

the oxime test

is for aldehydes and ketones, forms precipitate if positive

why is it necessary to ensure that the GCMS vial is more than half filled and not cloudy?

so syringe can takeup sample and so that the syringe won’t get clogged from cloudy sample

how to distinguish between primary alkyl amines and primary arylamines?

alkyl amines decompose immediately, while arylamines only decompose when warmed up

why don’t we use hydroxide in water as the base for the benzil diphenylacetone rxn?

the reactants aren’t soluble in water, we needed an organic solvent