CHEM 17 Lectures 12–21 Conceptual Recall

Vocabulary practice flashcards covering fundamental thermodynamic, kinetic, and mechanistic organic chemistry concepts from Lectures 12 through 21 of CHEM 17.

Thermodynamic Favorability ($\Delta G$)

The criterion where $\Delta G < 0$ favors the forward reaction under specified conditions and $\Delta G > 0$ favors the reverse reaction.

Standard Free Energy and Equilibrium ($\Delta G^\circ$)

The quantitative relationship given by $\Delta G^\circ = -RT \ln(K)$, where negative $\Delta G^\circ$ corresponds to $K > 1$ and positive $\Delta G^\circ$ corresponds to $K < 1$.

Activation Free Energy ($\Delta G^\ddagger$)

The free-energy difference between a reactant state and the transition state controlling a step, inversely relating to the rate constant exponentially via $k \propto \exp(-\Delta G^\ddagger / RT)$.

Transition State

A local maximum along the reaction coordinate on an energy diagram that represents a non-isolable species.

Reaction Intermediate

A local energy minimum between transition-state peaks that is formed in one elementary step and consumed in another.

Rate-Determining Step

The elementary step corresponding to the kinetically controlling barrier measured from the relevant preceding state in a multistep reaction.

Catalyst

A species that supplies a lower-barrier pathway for both forward and reverse processes without altering $\Delta G^\circ$ or the equilibrium constant $K$.

Carbonyl Electrophilicity

The electron-deficient character of the carbonyl carbon caused by polarization of the $\text{C=O}$ bond toward oxygen, yielding partial positive character and an accessible $\pi^*$ acceptor orbital.

Carbonyl Hyperconjugation

Electron donation from adjacent $\sigma$ bonds into the $\pi^*_{\text{C=O}}$ orbital, which raises the acceptor orbital energy and reduces electrophilicity.

Lithium Aluminum Hydride ($\text{LiAlH}_4$)

A strong hydride donor with reactive $\text{Al–H}$ bonds that reduces a wide range of carbonyl derivatives and requires strictly dry conditions due to violent reactions with protic solvents.

Sodium Borohydride ($\text{NaBH}_4$)

A mild hydride-reducing agent containing polarized $\text{B–H}$ bonds that is less reactive than $\text{LiAlH}_4$ and can tolerate some protic media.

Grignard Reagents

Organometallic reagents ($\text{R–MgX}$) with carbanion-like character at carbon due to the carbon-metal bond, acting as strong nucleophiles and strong bases that are quenched by proton donors.

Carbonyl Hydrate (gem-Diol)

The product of water addition across a carbonyl, whose equilibrium is favored by more electrophilic, sterically unhindered carbonyls and electron-withdrawing groups.

Microscopic Reversibility

The principle stating that the reverse reaction follows the exact same elementary pathway in reverse as the forward reaction, with electron-pushing arrows and proton transfers inverted.

Hemiacetal

A functional group containing a single tetrahedral carbon bonded to both an $\text{OH}$ group and an $\text{OR}$ group, formed under either acidic or basic conditions from an alcohol and a carbonyl.

Cyanohydrin

A functional group with the connectivity $\text{C(OH)(CN)}$, formed by nucleophilic addition of cyanide ($\text{CN}^-$) to a carbonyl followed by protonation of the resulting alkoxide.

Acyl Derivative Reactivity Ranking

The relative order of electrophilic acyl reactivity: acid chloride > acid anhydride > ester > amide, determined by heteroatom resonance donation and leaving group ability.

Addition–Elimination Mechanism

A two-step pathway characteristic of acyl substitution wherein a nucleophile adds to a $\text{C=O}$ to form a tetrahedral intermediate, which subsequently collapses to restore the $\text{C=O}$ and eject a leaving group.

Saponification

The base-promoted hydrolysis of an ester that is effectively irreversible because the produced carboxylic acid is immediately deprotonated to a stable carboxylate salt.

Fischer Esterification

The reversible, acid-catalyzed condensation of a carboxylic acid and an alcohol that establishes equilibrium with an ester and water.

Oxocarbenium Ion

A strongly electrophilic intermediate cation stabilized by resonance between an adjacent oxygen-bearing carbocation and an $\text{O=C}$ contributor.

Protecting Group

A functional modification (such as an acetal) that temporarily masks a reactive site against nucleophiles and bases, remains stable through subsequent reactions, and can be selectively cleaved.

Iminium Ion

A positively charged nitrogen-containing species within a $\text{C=N}$ system that is significantly more electrophilic than a neutral imine due to lower acceptor orbital energy.

Enamine

A condensation product formed from a carbonyl and a secondary amine via an iminium intermediate that deprotonates at the $\alpha$-carbon because no $\text{N–H}$ is present for loss.

Reductive Amination

A reaction pathway wherein cyanoborohydride delivers hydride to an iminium intermediate, forming a new $\text{C–H}$ bond to synthesize an amine.

$\text{S}_{\text{N}}2$ Reaction

A concerted bimolecular nucleophilic substitution characterized by the rate law $\text{Rate} = k[\text{substrate}][\text{nucleophile}]$, backside attack into $\sigma^*_{\text{C–LG}}$, and stereochemical inversion.

$\text{S}_{\text{N}}1$ Reaction

A stepwise unimolecular substitution characterized by the rate law $\text{Rate} = k[\text{substrate}]$, in which rate-determining ionization forms a planar carbocation intermediate before non-stereospecific nucleophilic attack.

E2 Elimination

A concerted bimolecular elimination described by $\text{Rate} = k[\text{substrate}][\text{base}]$ that requires an anti-periplanar spatial arrangement between the $\text{C–H}$ and $\text{C–LG}$ bonds.

E1 Elimination

A unimolecular elimination pathway governed by $\text{Rate} = k[\text{substrate}]$, where rate-limiting leaving-group ionization generates a carbocation that subsequently undergoes $\beta$-deprotonation.

Trans-Diaxial Requirement

The stereoelectronic constraint in cyclohexane rings requiring the leaving group and the $\beta$-hydrogen to simultaneously occupy adjacent axial positions to achieve the anti-periplanar geometry required for E2.

Hofmann Alkene Product

The less substituted alkene regioisomer predominantly formed in an E2 reaction when a sterically hindered bulky base selectively removes the more accessible $\beta$-hydrogen.

GFP Hierarchy

A systematic diagnostic framework used to predict competition among $\text{S}_{\text{N}}2$, $\text{E}2$, and $\text{S}_{\text{N}}1/\text{E}1$ pathways by evaluating $\text{S}_{\text{N}}2$ sterics/nucleophile first, $\text{E}2$ base strength second, and $\text{S}_{\text{N}}1/\text{E}1$ carbocation stability third.