DAT (Dental Admission Test) Organic Chemistry Syllabus

What are meso compounds?

Molecules containing stereocenters but possessing an internal plane of symmetry, making them achiral (optically inactive) despite having chiral centers.

What is the maximum number of stereoisomers for a molecule with n stereocenters?

2^n (fewer if meso forms or symmetry exist).

Define a chiral center (stereocenter) and the requirement for chirality.

A chiral center is a carbon bonded to four different groups. A molecule is chiral if it is non-superimposable on its mirror image (typically lacks an internal plane of symmetry).

State the steps for assigning R/S configuration.

Assign CIP priorities (1-4) by atomic number; orient lowest priority (4) away from viewer; if 1->2->3 is clockwise it is R, counterclockwise it is S (reverse if lowest priority points toward you).

In Fischer projections, what do horizontal and vertical lines represent?

Horizontal lines point toward the viewer (out of the page); vertical lines point away from the viewer (into the page).

Compare the relative stability of staggered versus eclipsed conformations of ethane.

Staggered is more stable (lower energy) because it minimizes torsional strain; eclipsed is highest energy due to eclipsing/torsional strain.

For cyclohexane, why is the chair conformation favored and where do bulky substituents prefer to sit?

The chair is most stable (no angle/torsional strain); bulky substituents prefer the equatorial position to avoid 1,3-diaxial strain.

Rank Newman projection conformations of butane by stability (most to least).

Anti (180 degrees) > gauche (60 degrees) > eclipsed > totally eclipsed/syn (0 degrees).

What is optical activity and what type of compound exhibits it?

The ability of a chiral substance to rotate plane-polarized light; exhibited by chiral molecules that are not racemic and not meso.

What is a racemic mixture and its observed optical rotation?

A 50:50 mixture of two enantiomers; it is optically inactive (net rotation = 0) because the rotations cancel.

What does specific rotation depend on, and what do (+)/dextrorotatory and (-)/levorotatory mean?

Specific rotation depends on the compound, concentration, path length, temperature, and wavelength. (+)/d rotates light clockwise; (-)/l rotates counterclockwise.

Compare SN1 and SN2 reactions in terms of kinetics and mechanism.

SN1: two steps, unimolecular, rate = k[substrate], via carbocation. SN2: one concerted step, bimolecular, rate = k[substrate][nucleophile], backside attack.

Which substrate (methyl, 1, 2, 3) favors SN1 and which favors SN2?

SN1 favors tertiary (3) substrates (stable carbocation); SN2 favors methyl and primary (1) substrates (least steric hindrance).

What stereochemical outcome does SN2 produce?

Inversion of configuration (Walden inversion) at the carbon due to backside attack.

What stereochemistry results from an SN1 reaction at a stereocenter?

Racemization (a mix of retention and inversion) because the planar carbocation can be attacked from either face.

Compare E1 and E2 elimination mechanisms.

E1: two steps via carbocation, unimolecular, rate = k[substrate]. E2: one concerted step, bimolecular, rate = k[substrate][base], requires anti-periplanar H and leaving group.

State Zaitsev's rule and Hofmann's exception.

Zaitsev: elimination favors the more substituted (more stable) alkene. Hofmann: bulky bases (e.g., t-butoxide) favor the less substituted alkene.

What geometric requirement must the H and leaving group satisfy for E2?

They must be anti-periplanar (180 degrees, antiperiplanar) in the same plane for concerted elimination.

Compare Markovnikov versus anti-Markovnikov addition to an alkene.

Markovnikov: H adds to the carbon with more hydrogens; the electrophile/positive part adds to give the more stable carbocation. Anti-Markovnikov (e.g., HBr with peroxides/radicals): reversed regiochemistry.

What product and stereochemistry result from catalytic hydrogenation of an alkene?

Syn addition of H2 across the double bond (both H atoms add to the same face) to give the alkane, using Pt/Pd/Ni catalyst.

What does hydroboration-oxidation (BH3 then H2O2/OH-) accomplish?

Anti-Markovnikov, syn addition of water across an alkene to give an alcohol (OH on the less substituted carbon).

What does oxymercuration-demercuration achieve regiochemically?

Markovnikov addition of water (OH on more substituted carbon) with no carbocation rearrangement.

Rank carbocation stability and name the stabilizing effects.

Stability: allylic/benzylic ~ tertiary > secondary > primary > methyl; stabilized by hyperconjugation, inductive electron donation from alkyl groups, and resonance (allylic/benzylic).

Rank free-radical stability.

Tertiary > secondary > primary > methyl (same trend as carbocations; stabilized by hyperconjugation and induction).

Why are carbanion stabilities opposite to carbocations regarding alkyl substitution?

Carbanions bear a negative charge, so electron-donating alkyl groups destabilize them: methyl > primary > secondary > tertiary in stability.

What is the general formula for an acyclic alkene and an alkyne?

Alkene (one C=C): CnH2n; alkyne (one C triple bond C): CnH2n-2.

What reagent set ozonolysis uses and what it produces from an alkene?

O3 followed by reductive workup (Zn/H2O or DMS) cleaves C=C to give two carbonyl compounds (aldehydes/ketones); oxidative workup gives carboxylic acids/ketones.

How are terminal alkynes distinguished chemically from internal alkynes?

Terminal alkynes have an acidic sp C-H (pKa ~25) that can be deprotonated by strong base (e.g., NaNH2) to form an acetylide nucleophile; internal alkynes cannot.

What is the product of oxidation of a primary alcohol with PCC versus with strong oxidants like KMnO4/Jones?

PCC (mild) gives an aldehyde; strong oxidants (KMnO4, CrO3/H2SO4) give a carboxylic acid. Secondary alcohols give ketones; tertiary alcohols do not oxidize.

How does the Williamson ether synthesis form an ether?

An alkoxide (R-O-) performs an SN2 attack on a primary alkyl halide; use the less hindered halide to avoid elimination.

Describe nucleophilic addition to a carbonyl by a Grignard reagent and the typical products.

The carbanion-like R-MgX adds to C=O; after acid workup: formaldehyde gives a primary alcohol, other aldehydes give secondary alcohols, ketones give tertiary alcohols, esters give tertiary alcohols (with two R added).

What is keto-enol tautomerism and which form usually predominates?

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

What is the product of an aldol condensation?

An enolate adds to a carbonyl to give a beta-hydroxy aldehyde/ketone (aldol), which on heating/dehydration gives an alpha,beta-unsaturated carbonyl (enone).

State Huckel's rule for aromaticity.

A planar, cyclic, fully conjugated ring is aromatic if it contains 4n+2 pi electrons (n = 0,1,2,...); 4n pi electrons makes it antiaromatic.

In electrophilic aromatic substitution, classify ortho/para directors versus meta directors.

Ortho/para directors are usually activating, electron-donating groups (e.g., -OH, -NH2, -OR, alkyl; halogens are o/p directing but deactivating). Meta directors are deactivating, electron-withdrawing groups (e.g., -NO2, -C=O, -SO3H, -CN).

Name the key electrophilic aromatic substitution reactions of benzene.

Halogenation (X2/FeX3), nitration (HNO3/H2SO4), sulfonation (SO3/H2SO4), Friedel-Crafts alkylation (RX/AlCl3), and Friedel-Crafts acylation (RCOCl/AlCl3).

In retrosynthetic analysis, what is a disconnection and a synthon?

A disconnection is the conceptual breaking of a bond to work backward from product to precursors; synthons are the idealized fragments (often charged) whose real reagent equivalents are used in synthesis.

In IR spectroscopy, what approximate absorptions identify O-H, C=O, and C triple-bond C/N?

O-H: broad ~3200-3550 cm-1 (carboxylic acid even broader ~2500-3300); C=O: strong sharp ~1700 cm-1; C triple bond: ~2100-2260 cm-1.

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

Chemical shift indicates the electronic/chemical environment (deshielding), integration gives the relative number of protons, and the n+1 rule gives the number of neighboring nonequivalent protons (multiplicity).

What does the molecular ion peak (M+) in mass spectrometry represent, and what is the M+2 clue for bromine/chlorine?

M+ gives the molecular weight of the compound. A roughly 1:1 M:M+2 ratio indicates bromine; a roughly 3:1 M:M+2 ratio indicates chlorine.

In extraction (a key lab technique), how do you separate a carboxylic acid from a neutral organic compound?

Wash the organic layer with aqueous base (NaHCO3/NaOH) to deprotonate the acid into a water-soluble carboxylate salt; it moves to the aqueous layer, leaving neutral compounds in the organic layer; then acidify to recover the acid.

What separation principle do distillation and recrystallization rely on?

Distillation separates liquids by differences in boiling point (vapor pressure); recrystallization purifies solids based on differential solubility (compound soluble when hot, crystallizes pure when cold while impurities stay in solution).