Organic Chemistry Exam 4 – Step-by-Step Study Guidance

Study Guide - Smart Notes

Tailored notes based on your materials, expanded with key definitions, examples, and context.

Q1. Select the IUPAC name for the given molecule.

Background

Topic: IUPAC Nomenclature of Alkenes and Substituted Hydrocarbons

This question tests your ability to apply IUPAC rules to name alkenes with substituents, including E/Z (cis/trans) stereochemistry and correct numbering of the carbon chain.

Key Terms and Concepts:

IUPAC Nomenclature: Systematic method for naming organic compounds.
E/Z Notation: Used for alkenes to specify the relative positions of substituents on double bonds.
Longest Chain: The parent chain must include the double bond and be numbered to give the double bond the lowest possible number.

Step-by-Step Guidance

Identify the longest carbon chain containing the double bond. Number the chain so that the double bond gets the lowest possible number.
Locate and identify all substituents (e.g., bromo, methyl) and assign their positions based on the numbering from step 1.
Determine the configuration (E or Z) of the double bond by assigning priorities to the groups attached to the double-bonded carbons using the Cahn-Ingold-Prelog rules.
Assemble the name: [E/Z]-[position]-[substituent]-[parent chain]-[ene].

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Q2. Which of the following is a carbene?

Background

Topic: Reactive Intermediates – Carbenes

This question tests your ability to recognize the structure of a carbene among several options.

Key Terms:

Carbene: A neutral molecule containing a divalent carbon atom with only six electrons in its valence shell (general formula: R2C:).
Carbenes can be singlet or triplet, but both have a carbon with two non-bonded electrons.

Step-by-Step Guidance

Examine each structure and look for a carbon atom with only two bonds and two non-bonded electrons (no formal charge).
Eliminate any structures where the carbon has a full octet or is charged.
Identify the structure that matches the definition of a carbene.

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Q3. Select the starting molecule(s) that will yield the given products under the given conditions.

Background

Topic: Organic Synthesis – Reaction Mechanisms and Reagents

This question tests your understanding of how specific reagents (e.g., CH2I2/Zn(Cu)) interact with different starting materials to produce cyclopropanation products.

Key Terms and Reagents:

Simmons–Smith Reaction: Converts alkenes to cyclopropanes using CH2I2 and Zn(Cu).
Recognize the functional groups present in the starting materials.

Step-by-Step Guidance

Identify the functional group in each starting material (e.g., alkene, alkyne, aromatic ring).
Recall which functional groups react with the given reagents to form the observed product (e.g., only alkenes undergo cyclopropanation with Simmons–Smith reagents).
Match the starting material(s) to the product based on the reaction type.

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Q4. Select the starting molecule(s) that will yield the given products under the given conditions.

Background

Topic: Electrophilic Addition and Substitution Reactions

This question tests your ability to predict the outcome of reactions involving Br2 in EtOH and OCH3 as a nucleophile.

Key Terms and Reagents:

Electrophilic Addition: Br2 adds to alkenes, forming bromonium ions, which can be attacked by nucleophiles like EtOH or OCH3.
Recognize the difference between Markovnikov and anti-Markovnikov addition.

Step-by-Step Guidance

Identify the functional group in each starting material (e.g., alkene, alkyne).
Recall the mechanism of Br2 addition in the presence of a nucleophile (EtOH or OCH3).
Determine which starting material(s) would react to give the observed product(s).

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Q5. Select the starting molecule(s) that will yield the given products under the given conditions.

Background

Topic: Radical Polymerization and Initiation

This question tests your understanding of how initiators and monomers interact to form polymers, and which starting materials are compatible with the given conditions.

Key Terms:

Initiator: A compound that generates radicals to start a chain reaction in polymerization.
Monomer: The small molecule that is polymerized.

Step-by-Step Guidance

Identify the structure of each starting material and determine if it contains a reactive double bond suitable for radical polymerization.
Recall the mechanism of radical initiation and propagation.
Determine which starting material(s) would yield the observed polymer product under the given conditions.

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Q6. Select the set of reagents that will achieve the given transformation.

Background

Topic: Alkene Addition Reactions – Oxymercuration, Hydroboration, and Acid-Catalyzed Addition

This question tests your ability to choose the correct reagents for converting an alkene to an ether or alcohol with specific regioselectivity and stereochemistry.

Key Terms and Reagents:

Oxymercuration-Demercuration: Adds H and OR across a double bond in Markovnikov fashion without rearrangement.
Hydroboration-Oxidation: Adds H and OH across a double bond in anti-Markovnikov fashion.
Acid-Catalyzed Addition: Adds H and OR across a double bond, but may allow rearrangement.

Step-by-Step Guidance

Analyze the transformation: what functional group is being added and at which position?
Recall the regioselectivity and stereochemistry of each reagent set.
Match the transformation to the correct reagent set based on the product structure.

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Q7. Select the set of reagents that will achieve the given transformation.

Background

Topic: Alkene Oxidation – Dihydroxylation and Epoxidation

This question tests your ability to choose reagents for converting alkenes to diols (vicinal dihydroxylation) or epoxides, and to understand the difference between syn and anti addition.

Key Terms and Reagents:

OsO4 (Osmium Tetroxide): Syn dihydroxylation (adds two OH groups on the same side).
m-CPBA (meta-Chloroperoxybenzoic acid): Epoxidation, which can be followed by acid or base hydrolysis to give anti diols.

Step-by-Step Guidance

Identify whether the transformation is syn or anti addition of OH groups.
Recall which reagent sets give syn vs. anti dihydroxylation.
Match the transformation to the correct reagent set.

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Q8. Select the set of reagents that will achieve the given transformation.

Background

Topic: Alkene Addition – Isotopic Labeling and Regioselectivity

This question tests your understanding of hydroboration-oxidation and oxymercuration-demercuration, especially with isotopically labeled reagents (e.g., BD3).

Key Terms and Reagents:

Hydroboration-Oxidation: Anti-Markovnikov addition of H and OH (or D and OH if using BD3).
Oxymercuration-Demercuration: Markovnikov addition of H and OR.

Step-by-Step Guidance

Analyze the product to determine where the isotopic label (D) ends up.
Recall the regioselectivity of each reagent set.
Match the transformation to the correct reagent set based on the product structure.

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Q9–17. Draw the major organic product(s) of the following reactions. If multiple stereoisomers are possible, draw all of them. Cross out any duplicates.

Background

Topic: Reaction Mechanisms and Stereochemistry

These questions test your ability to predict the major product(s) of various organic reactions, including addition, oxidation, reduction, and cleavage reactions. You must also consider stereochemistry and isotopic labeling where relevant.

Key Concepts:

Addition Reactions: e.g., Br2 addition, hydrogenation (H2/Pd), dihydroxylation (KMnO4).
Oxidative Cleavage: e.g., O3/DMS, KMnO4/H3O+.
Isotopic Labeling: Track the fate of labeled atoms (e.g., O*).
Stereochemistry: Draw all possible stereoisomers and eliminate duplicates.

Step-by-Step Guidance

Identify the type of reaction (addition, oxidation, reduction, cleavage, etc.).
Recall the mechanism and predict the regiochemistry and stereochemistry of the product(s).
Draw all possible products, considering stereochemistry and isotopic labeling.
Cross out any duplicate structures.

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Q18. Draw the mechanism of the following reaction. Show all arrow-pushing and intermediates. Ignore stereochemistry.

Background

Topic: Reaction Mechanisms – Arrow-Pushing

This question tests your ability to draw a detailed stepwise mechanism, including all intermediates and electron flow (curved arrows), for a given reaction.

Key Concepts:

Arrow-Pushing: Use curved arrows to show movement of electron pairs.
Intermediates: Draw all significant intermediates (carbocations, anions, etc.).

Step-by-Step Guidance

Identify the functional groups and reagents involved in the reaction.
Draw the starting material and show the first electron movement (e.g., protonation, nucleophilic attack).
Continue the mechanism stepwise, showing all intermediates and electron flow, until you reach the product.

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Q19. Draw the mechanism of the following reaction. Show all arrow-pushing and intermediates. Ignore stereochemistry.

Background

Topic: Reaction Mechanisms – Electrophilic Addition and Substitution

This question tests your ability to draw a detailed mechanism for a reaction involving HBr and dilute H3O+ with an alcohol or alkene.

Key Concepts:

Electrophilic Addition: Protonation of a double bond followed by nucleophilic attack.
Substitution: Possible SN1 or SN2 mechanism depending on the substrate.

Step-by-Step Guidance

Identify the functional groups and reagents involved.
Draw the starting material and show the first step (e.g., protonation, loss of leaving group).
Continue the mechanism, showing all intermediates and electron flow, until you reach the product.

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Q20. Is C20H20F22 saturated or unsaturated? Analyze the chemical formula, not the structure.

Background

Topic: Degrees of Unsaturation (Index of Hydrogen Deficiency)

This question tests your ability to determine whether a compound is saturated or unsaturated based solely on its molecular formula, considering the presence of halogens.

Key Formula:

Degrees of Unsaturation (DoU):

C = number of carbons
H = number of hydrogens
N = number of nitrogens
X = number of halogens (F, Cl, Br, I)

Step-by-Step Guidance

Identify the number of carbons (C), hydrogens (H), and halogens (F) in the formula.
Plug these values into the DoU formula above.
Interpret the result: DoU = 0 means saturated; DoU > 0 means unsaturated.

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Q21. (a) Which product – A or B – is the thermodynamically favored product? Explain your choice.

Background

Topic: Thermodynamic vs. Kinetic Control in Organic Reactions

This question tests your understanding of the difference between thermodynamic and kinetic products, and how to identify which is favored under certain conditions.

Key Concepts:

Kinetic Product: Forms faster, usually less stable.
Thermodynamic Product: Forms more slowly, but is more stable.
Thermodynamic control is favored at higher temperatures or with longer reaction times.

Step-by-Step Guidance

Analyze the structures of products A and B to determine which is more substituted or more stable.
Recall that the more stable (lower energy) product is thermodynamically favored.
Explain your reasoning based on the stability of the products.

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Q21. (b) Explain how to increase the yield of the thermodynamic product over the kinetic product.

Background

Topic: Reaction Conditions – Thermodynamic vs. Kinetic Control

This question tests your understanding of how reaction conditions (temperature, time, etc.) affect product distribution.

Key Concepts:

Thermodynamic product is favored at higher temperatures and with longer reaction times.
Kinetic product is favored at lower temperatures and with short reaction times.

Step-by-Step Guidance

Recall the conditions that favor thermodynamic control (e.g., higher temperature, reversible conditions).
Explain how adjusting these conditions would increase the yield of the thermodynamic product.

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Q22. (a) Describe in step-by-step detail how to separate benzoic acid from methyl benzoate using liquid-liquid extraction. Indicate what species are present in each layer at each step.

Background

Topic: Separation Techniques – Acid-Base Extraction

This question tests your understanding of how to use acid-base properties and solubility differences to separate organic compounds.

Key Terms and Reagents:

Benzoic Acid: Weak acid, can be deprotonated by base to form water-soluble benzoate ion.
Methyl Benzoate: Ester, neutral, remains in organic layer.
TBME: Organic solvent.
sat. NaHCO3: Weak base, reacts with benzoic acid.
6M HCl: Strong acid, used to re-protonate benzoate ion.
MgSO4: Drying agent.

Step-by-Step Guidance

Dissolve the mixture in TBME and add saturated NaHCO3. Benzoic acid reacts to form benzoate ion, which moves to the aqueous layer; methyl benzoate stays in the organic layer.
Separate the layers. The aqueous layer contains benzoate ion; the organic layer contains methyl benzoate.
Acidify the aqueous layer with 6M HCl to precipitate benzoic acid.
Dry the organic layer with anhydrous MgSO4 to remove water.

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Q22. (b) Which compound – benzoic acid or methyl benzoate – should have a higher Rf value on TLC?

Background

Topic: Chromatography – Thin Layer Chromatography (TLC)

This question tests your understanding of how polarity affects Rf values in TLC.

Key Concepts:

Rf Value: Ratio of distance traveled by compound to distance traveled by solvent front.
Less polar compounds travel further (higher Rf); more polar compounds interact more with the stationary phase (lower Rf).

Step-by-Step Guidance

Compare the polarity of benzoic acid (contains a carboxylic acid group) and methyl benzoate (contains an ester group).
Recall that more polar compounds have lower Rf values on silica gel TLC.
Predict which compound will have a higher Rf value.