Applied Organic Chemistry: Nucleophilic, Electrophilic, and Elimination Reactions

This set of vocabulary flashcards covers key mechanisms and concepts of nucleophilic substitution (SN1, SN2) and elimination reactions (E1, E2) as presented in the Applied Organic Chemistry lecture.

Nucleophile

An electron donator (Lewis base) that can possess a lone pair, a negative charge, a double bond, or a $\sigma$ bond between electropositive atoms.

$S_N1$ reaction

A unimolecular nucleophilic substitution reaction where the rate is only dependent on the concentration of the substrate, occurring in two steps with the first being rate-determining.

$S_N2$ reaction

A bimolecular nucleophilic substitution reaction involving a single step via a transition state where the rate depends on both the substrate and the nucleophile.

Racemization

The outcome of a chiral centre during an $S_N1$ reaction where the optical purity is lost, resulting in a mixture of enantiomers.

Inversion of stereochemistry

The stereochemical result of an $S_N2$ reaction where the nucleophile attacks from the rear at the same time as the leaving group departs.

Steric hindrance

A factor occurring in tertiary substrates that prevents $S_N2$ reactions and favors the $S_N1$ mechanism due to bulky groups blocking the reaction center.

Carbocation stability

The stability order of reaction intermediates where tertiary substrates are most stable and primary substrates are least stable; it determines the likelihood of $S_N1$ and $E1$ mechanisms.

Elimination Reaction

A reaction where a base removes a proton from an adjacent carbon atom to produce a double bond, rather than replacing a leaving group.

E1 Mechanism

A unimolecular elimination reaction where the stability of the carbocation is the most important factor, favored by polar protic solvents.

E2 Mechanism

A bimolecular elimination reaction that is more common than $E1$, requiring the proton, the carbon atoms, and the leaving group to be trans co-planar.

Bulky Base

Reagents such as $\text{t-BuOK}$, $\text{DBU}$, or $\text{LDA}$ that are used to drive a reaction towards an $E2$ mechanism.

Regioselectivity

The preference of a reaction to form specific regioisomeric alkenes, such as a trisubstituted versus a disubstituted alkene.

Stereoselectivity

The preference of a reaction to form specific stereoisomers, such as the formation of a trans-alkene over a cis-alkene.

Trans co-planar

The required geometric arrangement for an $E2$ elimination where the leaving group and the hydrogen atom being removed are on opposite sides of the molecule and in the same plane.

Electronic effects

A major theme in organic chemistry describing factors related to nucleophiles, leaving groups, and solvents that influence reaction outcomes.