Chem 351 Pre Class

Alkane

Saturated hydrocarbon with only single C-C and C-H bonds. General formula: C_n H_(2n+2). Sp3 hybridized carbons.

Alkene

Unsaturated hydrocarbon containing at least one C=C double bond. Sp2 hybridized carbons. General formula: C_n H_(2n).

Alkyne

Unsaturated hydrocarbon containing at least one C≡C triple bond. Sp hybridized carbons. Linear geometry around triple bond.

Alcohol

Functional group with an -OH (hydroxyl) group bonded to a sp3 carbon. Primary (1°), secondary (2°), or tertiary (3°).

Alkyl Halide (Haloalkane)

Compound containing a halogen (F, Cl, Br, I) bonded to an sp3 hybridized carbon.

Ether

Functional group featuring an oxygen atom single-bonded to two alkyl or aryl groups (R-O-R).

Aldehyde

Carbonyl group (C=O) bonded to at least one hydrogen atom (R-CHO). Located at the terminal end of a chain.

Ketone

Carbonyl group (C=O) bonded to two carbon groups (R-CO-R). Located internally in a carbon chain.

Carboxylic Acid

Functional group containing a carbonyl attached to a hydroxyl group (-COOH). Strongly acidic organic group (pKa ~4-5).

Ester

Carboxylic acid derivative where the -OH group is replaced by an -OR group (R-COO-R'). Often has a fruity aroma.

Amine

Nitrogen atom bonded to alkyl or aryl groups. Primary (1°: R-NH2), secondary (2°: R2NH), or tertiary (3°: R3N). Basic/nucleophilic.

Amide

Carbonyl group bonded directly to a nitrogen atom (R-CONR2). Resonance stabilization makes the C-N bond have partial double-bond character.

Constitutional Isomers

Compounds with the same molecular formula but different connectivity of atoms.

Stereoisomers

Compounds with the same molecular formula and atom connectivity, but different 3D spatial arrangements of atoms.

Chiral Center (Stereocenter)

A tetrahedral sp3 carbon atom bonded to four completely different groups.

Enantiomers

Non-superimposable mirror image stereoisomers. Opposite configuration (R vs S) at ALL chiral centers. Equal physical properties except optical rotation.

Diastereomers

Stereoisomers that are non-superimposable and NOT mirror images. Differ in configuration at some (but not all) chiral centers.

Meso Compound

An achiral molecule containing multiple stereocenters that has an internal plane of symmetry. Optically inactive.

R/S Configuration Rules (Cahn-Ingold-Prelog)

1. Assign priority 1-4 based on atomic number (highest = 1). 2. Point lowest priority (4) into the back (wedged/dashed). 3. Trace 1->2->3: Clockwise = R, Counterclockwise = S.

Newman Projection (Staggered vs Eclipsed)

Look down a C-C bond axis. Staggered is lowest energy (most stable). Eclipsed is highest energy due to torsional strain.

Chair Conformation (Axial vs Equatorial)

Stable ring conformation for cyclohexane. Substituents in equatorial positions are more stable due to lack of 1,3-diaxial steric interactions.

Bronsted-Lowry Acid vs Base

Acid = Proton (H+) donor. Base = Proton (H+) acceptor. Conjugate base forms after acid loses H+.

pKa Trend and Acid Strength

Lower pKa value = Stronger acid. The stronger the acid, the weaker and more stable its conjugate base.

ARIO Conjugate Base Stability Rules

Predicts acid strength by conjugate base stability: Atom (electronegativity/size), Resonance, Inductive effect, Orbital hybridization (sp > sp2 > sp3).

SN2 Mechanism

Bimolecular Nucleophilic Substitution. Concerted 1-step, backside attack, inversion of stereochemistry (Walden inversion). Favors 1° substrate, strong nucleophile, polar aprotic solvent.

SN1 Mechanism

Unimolecular Nucleophilic Substitution. 2-step mechanism via carbocation intermediate. Gives racemic mixture of stereocenters. Favors 3° substrate, weak nucleophile, polar protic solvent.

E2 Mechanism

Bimolecular Elimination. Concerted 1-step removal of proton and leaving group. Requires anti-periplanar geometry (H and LG 180° apart). Strong base favored.

E1 Mechanism

Unimolecular Elimination. 2-step mechanism via carbocation intermediate. Weak base/heat favored. Zaitsev's rule predicts the more substituted, stable alkene forms.

Carbocation Stability Trend

3° > 2° > 1° > Methyl. Stabilized by hyperconjugation and inductive donation from neighboring alkyl groups.

Polar Protic vs Polar Aprotic Solvents

Protic (H-bonding: H2O, MeOH, EtOH) stabilizes ions and favors SN1/E1. Aprotic (no H-bonding: DMSO, Acetone, DMF) leaves nucleophiles un-solvated, favoring SN2.

Zaitsev's Rule vs Hofmann's Rule

Zaitsev product = More substituted, more stable alkene (formed using small bases). Hofmann product = Less substituted alkene (formed using bulky bases like t-BuOK).