01 Mechanistic Foundations and Reactive Intermediates Free Online FlashCards

What do the tail and head of a full-headed curved arrow represent?

Its tail starts at an electron pair, and its head points to where that pair moves: an atom or a bond.

What does a lower $\mathrm{p}K_a$ indicate?

A lower $\mathrm{p}K_a$ indicates a stronger acid.

How does conjugate-base stability usually affect acidity?

Greater stabilization of the conjugate base usually means greater acidity, because the deprotonated form is more stable.

Why is acetate more stable than an alkoxide?

Resonance shares the negative charge between two oxygen atoms in acetate, making it more stable than an alkoxide with localized charge.

How does hybridization affect a carbon-bound negative charge?

For a carbon-bound negative charge, greater s-character generally stabilizes it more: $\mathrm{sp} > \mathrm{sp}^2 > \mathrm{sp}^3$.

Why are carbonyl $\alpha$-hydrogens more acidic than alkane hydrogens?

Removing an $\alpha$-hydrogen can form an enolate whose charge is resonance-stabilized, making these hydrogens more acidic than ordinary alkane hydrogens.

How do nucleophiles and bases differ?

A nucleophile donates an electron pair to form a bond; a base accepts a proton. One species can do either, depending on the reaction.

Why does nucleophilic attack at a carbonyl carbon move electrons onto oxygen?

A carbonyl carbon is electrophilic because the $\mathrm{C} = \mathrm{O}$ bond is polarized toward oxygen. Attack at carbon commonly moves the $\pi$ electrons onto oxygen.

What makes a group a good leaving group?

A good leaving group can accommodate the bonding electron pair after departure. The conjugate base of a strong acid is generally a weak base and a good leaving group.

How can an alcohol’s poor $-\mathrm{OH}$ leaving group be improved?

Protonation converts the poor leaving group $-\mathrm{OH}$ into water, which can depart as a neutral molecule.

How does a reaction intermediate differ from a transition state?

An intermediate forms in one step and is consumed in a later step. A transition state is a fleeting energy maximum, not an isolable intermediate.

What is the general stability order for simple alkyl carbocations?

Among simple alkyl carbocations, tertiary is generally more stable than secondary, primary, or methyl.