Portland Community College
WEIVER II MAXE
PCC
CHEM 210
Department of Chemistry · Organic Chemistry I
SCIENCE FOR THE COMMON GOOD
EST. 1961
Chem 210 — Exam II Review
R E A C T I O N M E C H A N I S M S · ST E R E O C H E M I ST R Y · CO N F O R M AT I O N S · I S O M E R I S M · C H I R A L I TY
INSTITUTION Portland Community College COURSE CODE CH 210
PROGRAM Organic Chemistry I · Science & ACADEMIC YEAR
Engineering Transfer
EXAM TITLE Chem 210 — Exam II: Mechanisms, TOTAL QUESTIONS 40 Questions
Stereochemistry & Conformations
COURSE TITLE Organic Chemistry I · Electrophilic FORMAT Multiple Choice / True-False — Select the
Additions · Stereochemistry · Single Best Answer
Conformational Analysis
STUDY GUIDE INSTRUCTIONS
▸ Questions cover electrophilic addition mechanisms, stereochemistry, conformational analysis, chirality, and isomer
classification.
▸ Select the single best answer for each question based on CHEM 210 Organic Chemistry I curriculum.
▸ Pay careful attention to carbocation stability, regioselectivity, and stereochemical relationships.
▸ Correct answers and detailed rationales appear below each question for comprehensive exam preparation.
ELECTROPHILIC ADDITION · STEREOCHEMISTRY · CONFORMATIONS · Questions 1
CHIRALITY · ISOMERISM – 40
1. Electrophiles are best defined as:
A. Electron-rich reagents seeking a nucleus to donate a pair of electrons
B. Electron-seeking reagents that have room to accept an electron pair
C. Neutral molecules that cannot accept electrons
D. Reagents that only react with water
CORRECT ANSWER B. Electron-seeking reagents that have room to accept an electron pair
RATIONALE Electrophiles ("electron-loving") are Lewis acids—electron-poor species with an empty orbital or incomplete
octet that can accept an electron pair. Examples: H⁺, carbocations (R₃C⁺), BH₃. Nucleophiles are electron-rich
Lewis bases that donate electron pairs. This distinction is fundamental to understanding all organic reaction
mechanisms.
, 2. What is the transition state in a chemical reaction?
A. The final products of the reaction
B. A stable intermediate that can be isolated
C. The highest-energy species lying between products and reactants
D. The starting materials before any reaction occurs
CORRECT ANSWER C. The highest-energy species lying between products and reactants
RATIONALE The transition state (‡) is the highest-energy, transient structure on the reaction coordinate—it cannot be
isolated. The free energy of activation (ΔG‡) is the energy barrier height from reactants to the transition state.
The transition state differs from an intermediate, which occupies a local energy minimum and may be stable
enough to detect or isolate.
3. In an electrophilic addition reaction with a strong acid, what are the two steps?
A. Deprotonate, then protonate
B. Protonate, then capture the carbocation
C. Protonate, capture, then deprotonate
D. Capture first, then protonate
CORRECT ANSWER B. Protonate, then capture the carbocation
RATIONALE Strong acid electrophilic addition to an alkene occurs in two steps: (1) protonation of the π bond—the
electrophile (H⁺) adds to one carbon of the double bond, forming the most stable carbocation; (2) capture—
the conjugate base (nucleophile) attacks the carbocation. Weak acid mechanisms require three steps:
protonate, capture, deprotonate.
4. Carbocation stability follows which order?
A. 1° > 2° > 3°
B. 3° > 2° > 1°
C. All carbocations are equally stable
D. 2° > 3° > 1°
CORRECT ANSWER B. 3° > 2° > 1°
RATIONALE Carbocation stability: tertiary (3°) > secondary (2°) > primary (1°) > methyl. Alkyl groups stabilize carbocations
through hyperconjugation (electron donation from adjacent C–H bonds into the empty p orbital) and
inductive effects. Resonance stabilization further increases stability. The more substituted the carbocation,
the more stable—this drives Markovnikov regioselectivity.
5. Regioselectivity in electrophilic addition is determined by:
A. The less stable carbocation forms faster
B. The more stable carbocation forms faster
C. Both carbocations form at equal rates
D. The solvent determines which carbocation forms
CORRECT ANSWER B. The more stable carbocation forms faster
RATIONALE Regioselectivity follows Markovnikov's rule: in electrophilic addition to an unsymmetrical alkene, the more
stable carbocation intermediate forms faster (lower activation energy), leading to the major product. The
hydrogen adds to the less substituted carbon (producing the more substituted, more stable carbocation). This
is a kinetic preference based on transition state energies.
WEIVER II MAXE
PCC
CHEM 210
Department of Chemistry · Organic Chemistry I
SCIENCE FOR THE COMMON GOOD
EST. 1961
Chem 210 — Exam II Review
R E A C T I O N M E C H A N I S M S · ST E R E O C H E M I ST R Y · CO N F O R M AT I O N S · I S O M E R I S M · C H I R A L I TY
INSTITUTION Portland Community College COURSE CODE CH 210
PROGRAM Organic Chemistry I · Science & ACADEMIC YEAR
Engineering Transfer
EXAM TITLE Chem 210 — Exam II: Mechanisms, TOTAL QUESTIONS 40 Questions
Stereochemistry & Conformations
COURSE TITLE Organic Chemistry I · Electrophilic FORMAT Multiple Choice / True-False — Select the
Additions · Stereochemistry · Single Best Answer
Conformational Analysis
STUDY GUIDE INSTRUCTIONS
▸ Questions cover electrophilic addition mechanisms, stereochemistry, conformational analysis, chirality, and isomer
classification.
▸ Select the single best answer for each question based on CHEM 210 Organic Chemistry I curriculum.
▸ Pay careful attention to carbocation stability, regioselectivity, and stereochemical relationships.
▸ Correct answers and detailed rationales appear below each question for comprehensive exam preparation.
ELECTROPHILIC ADDITION · STEREOCHEMISTRY · CONFORMATIONS · Questions 1
CHIRALITY · ISOMERISM – 40
1. Electrophiles are best defined as:
A. Electron-rich reagents seeking a nucleus to donate a pair of electrons
B. Electron-seeking reagents that have room to accept an electron pair
C. Neutral molecules that cannot accept electrons
D. Reagents that only react with water
CORRECT ANSWER B. Electron-seeking reagents that have room to accept an electron pair
RATIONALE Electrophiles ("electron-loving") are Lewis acids—electron-poor species with an empty orbital or incomplete
octet that can accept an electron pair. Examples: H⁺, carbocations (R₃C⁺), BH₃. Nucleophiles are electron-rich
Lewis bases that donate electron pairs. This distinction is fundamental to understanding all organic reaction
mechanisms.
, 2. What is the transition state in a chemical reaction?
A. The final products of the reaction
B. A stable intermediate that can be isolated
C. The highest-energy species lying between products and reactants
D. The starting materials before any reaction occurs
CORRECT ANSWER C. The highest-energy species lying between products and reactants
RATIONALE The transition state (‡) is the highest-energy, transient structure on the reaction coordinate—it cannot be
isolated. The free energy of activation (ΔG‡) is the energy barrier height from reactants to the transition state.
The transition state differs from an intermediate, which occupies a local energy minimum and may be stable
enough to detect or isolate.
3. In an electrophilic addition reaction with a strong acid, what are the two steps?
A. Deprotonate, then protonate
B. Protonate, then capture the carbocation
C. Protonate, capture, then deprotonate
D. Capture first, then protonate
CORRECT ANSWER B. Protonate, then capture the carbocation
RATIONALE Strong acid electrophilic addition to an alkene occurs in two steps: (1) protonation of the π bond—the
electrophile (H⁺) adds to one carbon of the double bond, forming the most stable carbocation; (2) capture—
the conjugate base (nucleophile) attacks the carbocation. Weak acid mechanisms require three steps:
protonate, capture, deprotonate.
4. Carbocation stability follows which order?
A. 1° > 2° > 3°
B. 3° > 2° > 1°
C. All carbocations are equally stable
D. 2° > 3° > 1°
CORRECT ANSWER B. 3° > 2° > 1°
RATIONALE Carbocation stability: tertiary (3°) > secondary (2°) > primary (1°) > methyl. Alkyl groups stabilize carbocations
through hyperconjugation (electron donation from adjacent C–H bonds into the empty p orbital) and
inductive effects. Resonance stabilization further increases stability. The more substituted the carbocation,
the more stable—this drives Markovnikov regioselectivity.
5. Regioselectivity in electrophilic addition is determined by:
A. The less stable carbocation forms faster
B. The more stable carbocation forms faster
C. Both carbocations form at equal rates
D. The solvent determines which carbocation forms
CORRECT ANSWER B. The more stable carbocation forms faster
RATIONALE Regioselectivity follows Markovnikov's rule: in electrophilic addition to an unsymmetrical alkene, the more
stable carbocation intermediate forms faster (lower activation energy), leading to the major product. The
hydrogen adds to the less substituted carbon (producing the more substituted, more stable carbocation). This
is a kinetic preference based on transition state energies.
