Organic Chemistry — Reactions & Mechanisms flashcards

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Acid–base reasoning, the SN1/SN2/E1/E2 decision, alkene and alkyne additions, radical halogenation, alcohol, ether and epoxide chemistry, Grignards and the Diels–Alder — asked the way exams ask: predict the product and explain what controls it.

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Learn deck · part of Organic Chemistry I/II · written against: Standard two-semester sequence; compound names use either the traditional locant style (1-butene, 2-propanol) or the IUPAC 2013 style (but-1-ene, propan-2-ol), both in wide use, and the nomenclature cards teach the 2013 rule. Updated 2026-10-10.

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One acid has $pK_a = 4.8$ and another has $pK_a = 16$ ⁠. Which is the stronger acid, and by roughly what factor?

The $pK_a = 4.8$ compound is the stronger acid — a lower $pK_a$ means a larger $K_a$ ⁠. Every $pK_a$ unit is a factor of ten, so it is roughly $10^{11}$ times stronger.

Why: $pK_a = -\log K_a$ ⁠, so the scale is logarithmic.
Acids & Bases
Basicity and nucleophilicity often go together, but what different things do they actually measure?

Basicity is thermodynamic — where the equilibrium for taking a proton lies. Nucleophilicity is kinetic — how fast a species attacks an electrophilic carbon. Size, polarizability and solvent can pull the two apart.
Nucleophiles · Bases & Leaving Groups
What is the rate law of an SN1 reaction, and why does the nucleophile not appear in it?

Rate $= k[RX]$ — unimolecular. The slow, rate-determining step is ionization to the carbocation; the nucleophile joins in a fast later step, so its concentration has no effect on the rate.
SN1 & Carbocations
What is the rate law of E2, and what geometric requirement must the substrate meet in the transition state?

Rate $= k[RX][\mathrm{base}]$ — bimolecular, one concerted step. The β-hydrogen and the leaving group must be anti-periplanar (dihedral angle 180°) so the breaking C–H σ bond can overlap with the C–X σ* orbital as the π bond forms.
E2 Elimination
How does E1 differ from E2 in its rate law, intermediate and stereochemical requirement?

E1 is unimolecular (rate $= k[RX]$ ⁠) and goes through a carbocation, so no anti-periplanar geometry is needed and the more substituted (mostly trans) Zaitsev alkene forms. It shares conditions with SN1: weak base, protic solvent, and heat tipping toward elimination.
E1 & Choosing the Pathway
1-Hexyne is hydrated with H₂SO₄ and HgSO₄. What carbonyl forms, and how would you get the other isomer?

2-Hexanone, a methyl ketone: Markovnikov addition gives an enol with OH on C2, which tautomerizes to the ketone. To reach hexanal instead, use hydroboration–oxidation with a bulky borane such as disiamylborane or 9-BBN.
Alkyne Reactions
Why does bromination of propane give mostly 2-bromopropane while chlorination gives a mixture of both isomers?

Bromine's hydrogen abstraction is endothermic with a late, product-like transition state, so it mirrors the radical stability difference and is highly selective (roughly 1 : 80 : 1600 for 1°, 2°, 3° hydrogens). Chlorine's step is exothermic with an early transition state, so it barely discriminates (about 1 : 4 : 5).

Why: the Hammond postulate.
Radical Halogenation
A primary alcohol is oxidized with (a) PCC in dichloromethane and (b) Jones reagent. What does each give?

(a) PCC stops at the aldehyde; (b) Jones reagent (CrO₃/H₂SO₄ in aqueous acetone) continues to the carboxylic acid via the aldehyde hydrate. Secondary alcohols give ketones with either; tertiary alcohols resist both.
Alcohol Reactions
After aqueous workup, what alcohol class does a Grignard reagent give with formaldehyde, with other aldehydes, with ketones, and with esters?

Formaldehyde gives a primary alcohol; other aldehydes a secondary alcohol; ketones a tertiary alcohol; esters consume two equivalents and give a tertiary alcohol bearing two identical R groups from the Grignard.
Grignard Reagents
What are the two partners in a Diels–Alder reaction, and what ring does it build?

A conjugated diene (4 π electrons) and a dienophile (2 π electrons, usually an alkene carrying electron-withdrawing groups) join in one concerted [4+2] cycloaddition to form a cyclohexene. No intermediates, so stereochemistry is transmitted faithfully.
Diels–Alder

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Review status: Second-reader reviewed, with corrections applied.

Checked against:

OpenStax Organic Chemistry: A Tenth Edition, consulted as a reference; no text copied.
Checked against Clayden, Greeves & Warren, Organic Chemistry, 2nd ed. (reference only; no text copied).

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