Conformations, Kinetics, Alkene/Alkyne Reactions, SN1/SN2/E1/E2, Carbonyls

What is the stability order of Newman conformations?

anti > gauche > eclipsed.

Why are eclipsed conformations high energy?

Torsional strain from electron repulsion.

What causes gauche strain?

Bulky groups 60° apart sterically repel.

Which cyclohexane conformation is most stable?

Chair.

Why are axial substituents less stable?

They experience 1,3-diaxial interactions.

How do you compare stability of disubstituted chairs?

Both equatorial = most stable.

How do you determine if cis/trans can be both equatorial?

Draw both chairs; check up/down orientation.

How do you determine reaction order from data?

Compare rate changes vs concentration changes; use ratios.

What does first-order mean?

Rate depends on concentration of one reactant.

What does zero-order mean?

Rate independent of reactant concentration.

How do you find overall reaction order?

Sum of exponents in the rate law.

Which mechanisms are first-order: SN1/E1 or SN2/E2?

SN1 and E1.

How do catalysts affect reactions?

Lower activation energy but do not change ΔG or equilibrium.

What does catalytic hydrogenation (H₂/Pt) do to alkenes?

Syn addition → alkane.

What does hydrohalogenation (H-X) do?

Markovnikov addition; H goes to less substituted carbon.

When is hydrohalogenation anti-Markovnikov?

HBr with ROOR (radical conditions) only.

What reagent performs acid-catalyzed hydration?

H₂O/H⁺ → Markovnikov alcohol.

What does halogenation (Br₂ or Cl₂) do?

Anti addition via halonium ion → vicinal dihalide.

What is a halohydrin?

Br and OH added anti; OH on more substituted carbon.

What does syn dihydroxylation give?

Syn 1,2-diol (KMnO₄ cold or OsO₄).

What does ozonolysis produce?

Carbonyl fragments (aldehydes/ketones).

What does full hydrogenation of an alkyne give?

Alkane (H₂/Pt).

What reagent gives cis-alkenes from alkynes?

Lindlar catalyst.

What reagent gives trans-alkenes from alkynes?

Na/NH₃ (dissolving metal).

What does oxymercuration of a terminal alkyne produce?

Enol → ketone (Markovnikov).

What does hydroboration-oxidation of a terminal alkyne produce?

Enol → aldehyde (anti-Markovnikov).

Which bases deprotonate terminal alkynes?

Strong bases like NaNH₂ or LDA.

What conditions favor SN2?

Primary substrate, strong nucleophile, polar aprotic solvent.

What conditions favor SN1?

Tertiary substrate, weak nucleophile, polar protic solvent.

What conditions favor E2?

Strong base + anti-periplanar β-H.

What conditions favor E1?

Tertiary substrate + weak base + heat.

What is leaving group ability order?

I⁻ > Br⁻ > Cl⁻ >>> F⁻.

Which substrates react fastest in SN2?

methyl > primary > secondary >>> tertiary.

Which substrates react fastest in SN1/E1?

tertiary > secondary >> primary.

When do carbocation rearrangements occur?

In SN1/E1 when a more stable carbocation can form.

What stereochemical requirement exists for E2?

β-H must be anti-periplanar to the leaving group.

What favors elimination over substitution?

Strong bulky base (t-BuOK) or high heat.

What do primary, secondary, and tertiary alcohols oxidize into?

1° → aldehyde → acid; 2° → ketone; 3° → no oxidation.

What does NaBH₄ reduce?

Aldehydes and ketones only.

What does LiAlH₄ reduce?

Aldehydes, ketones, carboxylic acids, and esters → alcohols.

What is produced when a Grignard reagent reacts with a ketone?

Tertiary alcohol (racemic if new stereocenter is formed).