Portland Community College
WEIVER 4 MAXE
PCC
CHEM 210
Department of Chemistry · Organic Chemistry I
SCIENCE FOR THE COMMON GOOD
EST. 1961
Chem 210 — Exam 4 Review
C A R B O C AT I O N S · C A R B A N I O N S · G R I G N A R D R E A G E N TS · E P OX I D AT I O N · A L KY N E H Y D R AT I O N ·
ST E R E O C H E M I ST R Y
INSTITUTION Portland Community College COURSE CODE CH 210
PROGRAM Organic Chemistry I · Science & ACADEMIC YEAR
Engineering Transfer
EXAM TITLE Chem 210 — Exam 4: Reactive TOTAL QUESTIONS 35 Questions
Intermediates, Epoxidation & Alkyne
Chemistry
COURSE TITLE Organic Chemistry I · Carbanions, FORMAT Multiple Choice / True-False — Select the
Carbocations, Oxidation & Single Best Answer
Stereochemistry
STUDY GUIDE INSTRUCTIONS
▸ Questions cover Grignard reagents, epoxidation mechanisms, alkyne hydration, carbocation/carbanion stability, and
stereochemical outcomes.
▸ Select the single best answer for each question based on CHEM 210 Organic Chemistry I curriculum.
▸ True/False questions require precise knowledge of stereochemical outcomes and reaction conditions.
▸ Correct answers and detailed rationales appear below each question for comprehensive exam preparation.
GRIGNARD · EPOXIDATION · ALKYNE HYDRATION · Questions
CARBOCATIONS/CARBANIONS · STEREOCHEMISTRY 1 – 35
1. Enantiomers are formed from what type of carbocation intermediate?
A. Chiral carbocation
B. Achiral carbocation
C. All carbocations produce enantiomers
D. Carbocations never produce enantiomers
CORRECT ANSWER A. Chiral carbocation
RATIONALE A chiral carbocation (with a stereocenter adjacent to the cationic center) can produce enantiomeric products
because the nucleophile can attack from either face of the planar sp²-hybridized carbocation. An achiral
carbocation produces a racemic mixture (if the product is chiral) or an achiral product. The planar geometry
of carbocations allows attack from both sides.
, 2. Grignard reagents attack which position of an epoxide?
A. The most substituted carbon
B. The least substituted carbon
C. Either carbon with equal probability
D. The oxygen atom directly
CORRECT ANSWER B. The least substituted carbon
RATIONALE Grignard reagents (RMgX) are strong nucleophiles that attack epoxides at the LEAST substituted (less
sterically hindered) carbon via an SN2-like backside mechanism. This is analogous to other nucleophilic
epoxide openings under basic conditions. The carbanion character of the Grignard reagent makes it a
powerful nucleophile, but steric accessibility governs regioselectivity.
3. Grignard reagents must be used under what conditions?
A. Strongly acidic conditions
B. Non-acidic (anhydrous, aprotic) conditions
C. Aqueous conditions
D. Any conditions—they are stable to everything
CORRECT ANSWER B. Non-acidic (anhydrous, aprotic) conditions
RATIONALE Grignard reagents (RMgX) are strong bases and nucleophiles that react violently with water, alcohols, and any
acidic protons. They must be prepared and used under rigorously anhydrous, aprotic conditions (dry ether or
THF). Exposure to acidic conditions causes proton transfer—the Grignard is simply protonated and destroyed
before it can act as a nucleophile.
4. Hyperconjugation is __________ for carbocations.
A. Stabilizing
B. Destabilizing
C. Neither—it has no effect
D. Only affects radicals
CORRECT ANSWER A. Stabilizing
RATIONALE Hyperconjugation stabilizes carbocations by donating electron density from adjacent C–H σ bonds into the
empty p orbital of the carbocation. More alkyl substituents = more hyperconjugation = greater stability. This
explains carbocation stability order: 3° > 2° > 1° > methyl. For carbanions, hyperconjugation is DESTABILIZING
because electron donation into an already electron-rich center increases energy.
5. Hyperconjugation is __________ for carbanions.
A. Stabilizing
B. Destabilizing
C. Neither—it has no effect
D. Only affects carbocations
CORRECT ANSWER B. Destabilizing
RATIONALE Carbanions are electron-rich (negative charge, lone pair). Hyperconjugation donates electron density from
adjacent C–H bonds into the already electron-rich carbanion center—this increases electron-electron
repulsion and destabilizes the carbanion. Therefore, carbanion stability follows the opposite trend of
carbocations: methyl > 1° > 2° > 3° (less substituted is more stable).
WEIVER 4 MAXE
PCC
CHEM 210
Department of Chemistry · Organic Chemistry I
SCIENCE FOR THE COMMON GOOD
EST. 1961
Chem 210 — Exam 4 Review
C A R B O C AT I O N S · C A R B A N I O N S · G R I G N A R D R E A G E N TS · E P OX I D AT I O N · A L KY N E H Y D R AT I O N ·
ST E R E O C H E M I ST R Y
INSTITUTION Portland Community College COURSE CODE CH 210
PROGRAM Organic Chemistry I · Science & ACADEMIC YEAR
Engineering Transfer
EXAM TITLE Chem 210 — Exam 4: Reactive TOTAL QUESTIONS 35 Questions
Intermediates, Epoxidation & Alkyne
Chemistry
COURSE TITLE Organic Chemistry I · Carbanions, FORMAT Multiple Choice / True-False — Select the
Carbocations, Oxidation & Single Best Answer
Stereochemistry
STUDY GUIDE INSTRUCTIONS
▸ Questions cover Grignard reagents, epoxidation mechanisms, alkyne hydration, carbocation/carbanion stability, and
stereochemical outcomes.
▸ Select the single best answer for each question based on CHEM 210 Organic Chemistry I curriculum.
▸ True/False questions require precise knowledge of stereochemical outcomes and reaction conditions.
▸ Correct answers and detailed rationales appear below each question for comprehensive exam preparation.
GRIGNARD · EPOXIDATION · ALKYNE HYDRATION · Questions
CARBOCATIONS/CARBANIONS · STEREOCHEMISTRY 1 – 35
1. Enantiomers are formed from what type of carbocation intermediate?
A. Chiral carbocation
B. Achiral carbocation
C. All carbocations produce enantiomers
D. Carbocations never produce enantiomers
CORRECT ANSWER A. Chiral carbocation
RATIONALE A chiral carbocation (with a stereocenter adjacent to the cationic center) can produce enantiomeric products
because the nucleophile can attack from either face of the planar sp²-hybridized carbocation. An achiral
carbocation produces a racemic mixture (if the product is chiral) or an achiral product. The planar geometry
of carbocations allows attack from both sides.
, 2. Grignard reagents attack which position of an epoxide?
A. The most substituted carbon
B. The least substituted carbon
C. Either carbon with equal probability
D. The oxygen atom directly
CORRECT ANSWER B. The least substituted carbon
RATIONALE Grignard reagents (RMgX) are strong nucleophiles that attack epoxides at the LEAST substituted (less
sterically hindered) carbon via an SN2-like backside mechanism. This is analogous to other nucleophilic
epoxide openings under basic conditions. The carbanion character of the Grignard reagent makes it a
powerful nucleophile, but steric accessibility governs regioselectivity.
3. Grignard reagents must be used under what conditions?
A. Strongly acidic conditions
B. Non-acidic (anhydrous, aprotic) conditions
C. Aqueous conditions
D. Any conditions—they are stable to everything
CORRECT ANSWER B. Non-acidic (anhydrous, aprotic) conditions
RATIONALE Grignard reagents (RMgX) are strong bases and nucleophiles that react violently with water, alcohols, and any
acidic protons. They must be prepared and used under rigorously anhydrous, aprotic conditions (dry ether or
THF). Exposure to acidic conditions causes proton transfer—the Grignard is simply protonated and destroyed
before it can act as a nucleophile.
4. Hyperconjugation is __________ for carbocations.
A. Stabilizing
B. Destabilizing
C. Neither—it has no effect
D. Only affects radicals
CORRECT ANSWER A. Stabilizing
RATIONALE Hyperconjugation stabilizes carbocations by donating electron density from adjacent C–H σ bonds into the
empty p orbital of the carbocation. More alkyl substituents = more hyperconjugation = greater stability. This
explains carbocation stability order: 3° > 2° > 1° > methyl. For carbanions, hyperconjugation is DESTABILIZING
because electron donation into an already electron-rich center increases energy.
5. Hyperconjugation is __________ for carbanions.
A. Stabilizing
B. Destabilizing
C. Neither—it has no effect
D. Only affects carbocations
CORRECT ANSWER B. Destabilizing
RATIONALE Carbanions are electron-rich (negative charge, lone pair). Hyperconjugation donates electron density from
adjacent C–H bonds into the already electron-rich carbanion center—this increases electron-electron
repulsion and destabilizes the carbanion. Therefore, carbanion stability follows the opposite trend of
carbocations: methyl > 1° > 2° > 3° (less substituted is more stable).
