CHEM 233 Final Exam(latest version 2021)

CHEM 233 Final Exam

What are saturated vs unsaturated fatty acids?
Correct answer- •Saturated fatty acids have no C=C bonds (their C's have max # of Hs)
•Unsaturated fatty acids have one or more C=C bonds (monosaturated = one double
bond) (polyunsaturated = more than 1 double bond)
•Z (cis) are naturally occurring double bonds; E (trans) are artificial double bonds

How is biodiesel produced commercially? Which method is predominant?
Correct answer- ***1) Base catalyzed transesterification of oil with alcohol
2) Acid catalyzed esterification of the oil with methanol
3) Saponification of the oil to yield free fatty acids, followed by acid catalyzed
esterification

Transesterification
Correct answer- conversion of one ester into another through a substitution reaction
with an alcohol (alkoxy group)

Reaction transesterification
Correct answer- ester 1 + alcohol--> ester 2

Making Biodiesel FAMEs
Correct answer- Triglyceride --> in CH3OH & catalytic CH3O- Na+--> FAMEs

What does FAME and NMR stand for? Correct answer- •FAME: Fatty acid methyl esters
•NMR: Nuclear Magnetic Resonance

In biodiesel lab, what is the limiting reagent?
Which reagent is in excess and why is it required in excess?
Correct answer- •L.R. is triglyceride
•Methanol is the reagent required in excess so equilibrium can be shifted to the right to
produce more product

In biodiesel lab, what is the effect of water on sodium methoxide?
Correct answer- NaOMe + H2O -> MeOH + NaOH

In biodiesel lab, how will the product be characterized?
Correct answer- •H-NMR
•Prominent peak due to -OCH3; singlet at 4.1 ppm
•Lack of glyceryl hydrogens; lack of multiplet at 4.0 - 4.4 ppm

In biodiesel lab, how is waste disposed?
Correct answer- •Organic liquid hazardous waste container

, NMR Peaks Correct answer-

In biodiesel lab, how is Le-Chatelier's principle applicable to the transesterification
reaction in the preparation of FAMEs?
Correct answer- • Large amts of methanol will increase the product.

Ratio of proton peak (integrated area)
Correct answer- Methoxy protons/Bis-allylic protons

In Pentacene lab, what is the purpose of base in the aldol condenstation reaction?
Correct answer- •In the aldol condensation rxn, the base catalyzes nucleophilic addition
to the carbonyl group and also regenerates the hydroxide ion.

Hexynide lithium reacts with 6, 13-pentacenequinone via:
a) substitution reaction
b) elimination reaction
c) nucleophilic addition to carbonyl
d) electrophilic addition to carbonyl
e) condensation
Correct answer- c) nucleophilic addition to carbonyl

What is the role of tin(II) chloride (SnCl2) in the synthesis of pentacene derivative?
Correct answer- •Tin(II) (SnCl2) chloride adds electrons to the pentacene derivative
compound increasing its double bonds and making the compound aromatic

At the end of step 2 in the pentacene lab, where would you dispose the waste
containing tin salts?
Correct answer- •Hazardous aqueous liquid acidic/basic waste container

What is the stationary phase in the column chromatographic purification of crude
pentacene derivative?
Correct answer- • Silica Gel (SiO2)

The elimination step of the aldol condensation reaction is an example of ___________.
Correct answer- • E1CB

True or false: Increasing the conjugation will decrease the energy of absorption.
Correct answer- • True

What major differences would you be looking for in the IR spectra of 6, 13-
pentacenequinone of 6, 13- dihexynylpentacene?
Correct answer- • IR spectra of 6, 13-pentacenequinone: characteristic absorption for
the 2 carbonyl groups (C=O) will occur around 1800-1650 cm-1 with a strong intensity.
• For 6,13-dihexynylpentacene, IR spectra will show a medium peak around 2150 cm-1
for C≡C and a strong peak around 3000-2850 cm-1 for Csp3-H.