OAT (Optometry Admission Test) Organic Chemistry Syllabus

What is the relationship between specific rotation and enantiomeric excess?

Observed rotation reflects ee; %ee = (observed rotation / rotation of pure enantiomer) x 100, and also equals %major - %minor enantiomer.

In an SN2 reaction, what happens to the stereochemistry at the reacting carbon?

Inversion of configuration (Walden inversion) because the nucleophile attacks the backside opposite the leaving group.

What stereochemical outcome results from an SN1 reaction at a chiral center?

Racemization (a mix of retention and inversion) because the planar carbocation intermediate is attacked from both faces.

Compare SN1 and SN2 in terms of kinetics, substrate preference, and nucleophile strength.

SN1: first-order, favors 3 degree substrates, weak nucleophile/polar protic solvent, carbocation intermediate. SN2: second-order, favors methyl/1 degree, strong nucleophile/polar aprotic solvent, concerted.

How does leaving group ability trend, and why?

Better leaving groups are weaker bases (more stable anions): I- > Br- > Cl- > F-, and tosylate/triflate are excellent; OH-, NH2-, and R-O- are poor leaving groups.

What is the difference between E1 and E2 elimination in mechanism and kinetics?

E2: concerted, second-order, strong base, anti-periplanar geometry. E1: stepwise via carbocation, first-order, weak base, favored by polar protic solvent.

State Zaitsev's rule and Hofmann's rule for elimination.

Zaitsev: the more substituted (more stable) alkene predominates. Hofmann: the less substituted alkene predominates, favored by bulky bases (e.g., t-butoxide).

What geometric requirement must be met for an E2 reaction?

The H and leaving group must be anti-periplanar (180 degrees dihedral angle); in cyclohexanes both must be axial (trans-diaxial).

What is Markovnikov's rule for electrophilic addition to alkenes?

In HX addition, the H adds to the carbon with more hydrogens and the X (electrophile's partner) adds to the more substituted carbon, forming the more stable carbocation.

What reagents give anti-Markovnikov addition of water and of HBr to an alkene?

Anti-Markovnikov hydration: hydroboration-oxidation (BH3 then H2O2/OH-). Anti-Markovnikov HBr: HBr with peroxides (radical mechanism).

What is the product and stereochemistry of alkene bromination (Br2)?

A vicinal dibromide formed with anti addition via a cyclic bromonium ion intermediate.

What does ozonolysis (O3 then Zn/H2O) do to an alkene?

It cleaves the C=C double bond, converting each carbon into a carbonyl (aldehyde or ketone), splitting the molecule.

What is the stereochemistry of catalytic hydrogenation (H2/Pd) of an alkene?

Syn addition of two hydrogens to the same face of the double bond.

Rank carbocation stability and explain why.

3 degree > 2 degree > 1 degree > methyl, because alkyl groups donate electron density (hyperconjugation and induction) stabilizing the positive charge; resonance/allylic stabilization further increases it.

What is a carbocation rearrangement and when does it occur?

A 1,2-hydride or 1,2-alkyl shift that converts a less stable carbocation into a more stable one; common in SN1/E1 and electrophilic addition reactions.

Rank free-radical stability and name a reaction that proceeds through radicals.

3 degree > 2 degree > 1 degree > methyl (same factors as carbocations); radical halogenation of alkanes and anti-Markovnikov HBr addition proceed via radicals.

What are the three steps of a radical chain mechanism?

Initiation (homolysis to form radicals), propagation (radicals react to make products and new radicals), and termination (two radicals combine).

How does an epoxide ring open under acidic versus basic conditions?

Acidic: nucleophile attacks the more substituted carbon (more carbocation character). Basic: nucleophile attacks the less hindered (less substituted) carbon (SN2-like).

How are alcohols classified, and how does oxidation differ among them?

Primary alcohols oxidize to aldehydes then carboxylic acids (PCC stops at aldehyde); secondary to ketones; tertiary alcohols resist oxidation (no alpha H on the C-OH).

What reagent converts a primary alcohol to an aldehyde without over-oxidation?

PCC (pyridinium chlorochromate) in anhydrous conditions (or other mild oxidants like Dess-Martin periodinane).

What is the Williamson ether synthesis?

An SN2 reaction of an alkoxide (R-O-) with a primary alkyl halide to form an ether; works best with unhindered substrates.

What is keto-enol tautomerism?

An equilibrium between a keto form (C=O with alpha C-H) and an enol form (C=C-OH); the keto form is usually more stable.

Why is the carbonyl carbon electrophilic, and how does aldehyde reactivity compare to ketone reactivity?

The C=O carbon is electrophilic due to oxygen's electronegativity; aldehydes are more reactive than ketones because they are less sterically hindered and less stabilized by electron-donating alkyl groups.

What product forms when a Grignard reagent reacts with a ketone after aqueous workup?

A tertiary alcohol (Grignard adds an R group to the carbonyl carbon, forming a new C-C bond).

What is formed when an aldehyde/ketone reacts with a primary amine versus a secondary amine?

Primary amine gives an imine (Schiff base, C=N-R); secondary amine gives an enamine (C=C-N).

What is the difference between a hemiacetal and an acetal?

A hemiacetal has one OR and one OH on the same carbon (from one alcohol addition); an acetal has two OR groups (from two alcohols, with loss of water), and acetals serve as protecting groups.

What is the general requirement for aromaticity (Huckel's rule)?

The molecule must be cyclic, planar, fully conjugated (continuous p-orbitals), and contain (4n + 2) pi electrons (e.g., 2, 6, 10).

How do electron-donating and electron-withdrawing groups direct electrophilic aromatic substitution?

Activating groups (e.g., -OH, -NH2, alkyl) are ortho/para directors; deactivating groups (e.g., -NO2, -C=O, -SO3H) are meta directors; halogens are deactivating but ortho/para directing.

How does basicity of amines compare to amides, and why?

Amines are basic (lone pair available on N); amides are far less basic because the nitrogen lone pair is delocalized into the carbonyl by resonance.

In IR spectroscopy, what characteristic absorptions identify O-H, C=O, and N-H bonds?

O-H: broad ~3200-3550 cm-1; N-H: ~3300-3500 cm-1 (sharper, may be doublet for primary amine); C=O: strong ~1700-1750 cm-1.

In 1H NMR, what do chemical shift, integration, and splitting (n+1 rule) each tell you?

Chemical shift indicates the electronic/chemical environment (deshielding); integration gives the relative number of protons; splitting (n+1) gives the number of neighboring nonequivalent protons.