CHM 2210 Exam 4 V3 | CHM 2210 Organic Chemistry I | Actual Q&A
with Rationale (CHM2210 Exam 4) | University of Central Florida
1. Which reagent would best facilitate the conversion of 1-butanol to 1-bromobutane via an
SN2 mechanism while minimizing rearrangement?
A. HBr, heat
B. PBr3
C. NaBr, H2SO4
D. Br2, FeBr3
Answer: B
Explanation: Phosphorus tribromide (PBr3) is the preferred reagent for converting
primary and secondary alcohols into alkyl bromides because it avoids the formation of
carbocations. Using HBr often leads to carbocation intermediates which can undergo
rearrangements to more stable forms. PBr3 proceeds through an SN2 pathway, ensuring
the stereochemistry is inverted and the carbon skeleton remains intact.
2. In the 1H NMR spectrum of 2-propanol, what is the expected splitting pattern for the
methine (CH) proton?
A. Doublet
B. Quartet
C. Septet
D. Singlet
Answer: C
Explanation: The methine proton in 2-propanol is adjacent to two equivalent methyl
groups, totaling six neighboring protons. According to the n+1 rule, the signal will be split
into 6+1, which is a septet. The hydroxyl proton itself often appears as a singlet due to
rapid exchange, but the coupling between the CH and the six methyl protons is distinct.
3. Which of the following compounds will show a strong, broad absorption band near 3300
cm^-1 in its IR spectrum?
A. Hexane
B. 2-Hexanone
C. Hexanal
D. 1-Hexanol
,Answer: D
Explanation: The absorption band near 3300 cm^-1 is characteristic of the O-H stretching
vibration in alcohols. This band is typically broad due to the effects of extensive hydrogen
bonding between molecules. Carbonyl compounds like ketones and aldehydes show a
sharp peak around 1700 cm^-1 instead.
4. What is the major product formed when 1-methylcyclopentene reacts with MCPBA
followed by aqueous acid?
A. 1-methylcyclopentane-1,2-diol (trans)
B. 1-methylcyclopentane-1,2-diol (cis)
C. 2-methylcyclopentanol
D. 1-methylcyclopentanol
Answer: A
Explanation: Reaction with MCPBA forms an epoxide intermediate across the double
bond. Subsequent acid-catalyzed ring opening involves an anti-addition of water to the
epoxide. This results in the formation of a trans-diol, where the two hydroxyl groups are on
opposite faces of the ring.
5. Which reagent is most suitable for oxidizing a primary alcohol to an aldehyde without
further oxidation to a carboxylic acid?
A. KMnO4, NaOH
B. CrO3, H2SO4
C. Na2Cr2O7, H2SO4
D. PCC (Pyridinium chlorochromate)
Answer: D
Explanation: PCC is a mild oxidizing agent that stops at the aldehyde stage for primary
alcohols. Stronger reagents like Jones reagent (CrO3/H2SO4) or potassium permanganate
will further oxidize the aldehyde to a carboxylic acid. Using PCC in anhydrous solvents like
dichloromethane ensures the intermediate hydrate cannot form, preventing over-
oxidation.
6. Which of the following ethers is best synthesized using the Williamson ether synthesis?
A. Di-tert-butyl ether
B. Diphenyl ether
C. Methyl t-butyl ether
D. Neopentyl phenyl ether
, Answer: C
Explanation: Williamson ether synthesis involves an SN2 reaction between an alkoxide
and a primary alkyl halide. To synthesize methyl t-butyl ether, one should react potassium
t-butoxide with methyl iodide. If the reverse were attempted (methoxide with t-butyl
bromide), E2 elimination would dominate because the halide is tertiary.
7. Predict the product of the reaction between phenylmagnesium bromide and
formaldehyde, followed by acid workup.
A. Phenol
B. Benzoic acid
C. Acetophenone
D. Benzyl alcohol
Answer: D
Explanation: Formaldehyde reacts with Grignard reagents to produce primary alcohols
after protonation. Phenylmagnesium bromide adds a phenyl group to the single carbon of
formaldehyde. The resulting alkoxide is then protonated during workup to yield benzyl
alcohol.
8. In 1H NMR, what is the characteristic chemical shift range for a proton attached to a
carbon that is also attached to an oxygen (R-CH2-OH)?
A. 3.3 - 4.5 ppm
B. 2.0 - 2.5 ppm
C. 0.9 - 1.5 ppm
D. 6.5 - 8.0 ppm
Answer: A
Explanation: Electronegative atoms like oxygen deshield adjacent protons, shifting their
resonance downfield. Protons on a carbon alpha to an alcohol or ether group typically
appear in the 3.3 to 4.5 ppm range. Protons in the 6.5-8.0 range are usually aromatic, while
those below 2 ppm are typically alkyl protons.
9. What is the major product when 2,2-dimethyloxirane reacts with sodium methoxide in
methanol?
A. 2-methoxy-2-methylpropene
B. 2-methoxy-2-methylpropan-1-ol
C. 2,2-dimethyl-1,2-ethanediol
D. 1-methoxy-2-methylpropan-2-ol
with Rationale (CHM2210 Exam 4) | University of Central Florida
1. Which reagent would best facilitate the conversion of 1-butanol to 1-bromobutane via an
SN2 mechanism while minimizing rearrangement?
A. HBr, heat
B. PBr3
C. NaBr, H2SO4
D. Br2, FeBr3
Answer: B
Explanation: Phosphorus tribromide (PBr3) is the preferred reagent for converting
primary and secondary alcohols into alkyl bromides because it avoids the formation of
carbocations. Using HBr often leads to carbocation intermediates which can undergo
rearrangements to more stable forms. PBr3 proceeds through an SN2 pathway, ensuring
the stereochemistry is inverted and the carbon skeleton remains intact.
2. In the 1H NMR spectrum of 2-propanol, what is the expected splitting pattern for the
methine (CH) proton?
A. Doublet
B. Quartet
C. Septet
D. Singlet
Answer: C
Explanation: The methine proton in 2-propanol is adjacent to two equivalent methyl
groups, totaling six neighboring protons. According to the n+1 rule, the signal will be split
into 6+1, which is a septet. The hydroxyl proton itself often appears as a singlet due to
rapid exchange, but the coupling between the CH and the six methyl protons is distinct.
3. Which of the following compounds will show a strong, broad absorption band near 3300
cm^-1 in its IR spectrum?
A. Hexane
B. 2-Hexanone
C. Hexanal
D. 1-Hexanol
,Answer: D
Explanation: The absorption band near 3300 cm^-1 is characteristic of the O-H stretching
vibration in alcohols. This band is typically broad due to the effects of extensive hydrogen
bonding between molecules. Carbonyl compounds like ketones and aldehydes show a
sharp peak around 1700 cm^-1 instead.
4. What is the major product formed when 1-methylcyclopentene reacts with MCPBA
followed by aqueous acid?
A. 1-methylcyclopentane-1,2-diol (trans)
B. 1-methylcyclopentane-1,2-diol (cis)
C. 2-methylcyclopentanol
D. 1-methylcyclopentanol
Answer: A
Explanation: Reaction with MCPBA forms an epoxide intermediate across the double
bond. Subsequent acid-catalyzed ring opening involves an anti-addition of water to the
epoxide. This results in the formation of a trans-diol, where the two hydroxyl groups are on
opposite faces of the ring.
5. Which reagent is most suitable for oxidizing a primary alcohol to an aldehyde without
further oxidation to a carboxylic acid?
A. KMnO4, NaOH
B. CrO3, H2SO4
C. Na2Cr2O7, H2SO4
D. PCC (Pyridinium chlorochromate)
Answer: D
Explanation: PCC is a mild oxidizing agent that stops at the aldehyde stage for primary
alcohols. Stronger reagents like Jones reagent (CrO3/H2SO4) or potassium permanganate
will further oxidize the aldehyde to a carboxylic acid. Using PCC in anhydrous solvents like
dichloromethane ensures the intermediate hydrate cannot form, preventing over-
oxidation.
6. Which of the following ethers is best synthesized using the Williamson ether synthesis?
A. Di-tert-butyl ether
B. Diphenyl ether
C. Methyl t-butyl ether
D. Neopentyl phenyl ether
, Answer: C
Explanation: Williamson ether synthesis involves an SN2 reaction between an alkoxide
and a primary alkyl halide. To synthesize methyl t-butyl ether, one should react potassium
t-butoxide with methyl iodide. If the reverse were attempted (methoxide with t-butyl
bromide), E2 elimination would dominate because the halide is tertiary.
7. Predict the product of the reaction between phenylmagnesium bromide and
formaldehyde, followed by acid workup.
A. Phenol
B. Benzoic acid
C. Acetophenone
D. Benzyl alcohol
Answer: D
Explanation: Formaldehyde reacts with Grignard reagents to produce primary alcohols
after protonation. Phenylmagnesium bromide adds a phenyl group to the single carbon of
formaldehyde. The resulting alkoxide is then protonated during workup to yield benzyl
alcohol.
8. In 1H NMR, what is the characteristic chemical shift range for a proton attached to a
carbon that is also attached to an oxygen (R-CH2-OH)?
A. 3.3 - 4.5 ppm
B. 2.0 - 2.5 ppm
C. 0.9 - 1.5 ppm
D. 6.5 - 8.0 ppm
Answer: A
Explanation: Electronegative atoms like oxygen deshield adjacent protons, shifting their
resonance downfield. Protons on a carbon alpha to an alcohol or ether group typically
appear in the 3.3 to 4.5 ppm range. Protons in the 6.5-8.0 range are usually aromatic, while
those below 2 ppm are typically alkyl protons.
9. What is the major product when 2,2-dimethyloxirane reacts with sodium methoxide in
methanol?
A. 2-methoxy-2-methylpropene
B. 2-methoxy-2-methylpropan-1-ol
C. 2,2-dimethyl-1,2-ethanediol
D. 1-methoxy-2-methylpropan-2-ol
