Organic Chemistry Review Flashcards

Flashcards for reviewing key organic chemistry concepts, reactions, and spectroscopic techniques.

SN1 Reaction

Unimolecular nucleophilic substitution; 2 steps: carbocation formation then nucleophile attack. Favored by tertiary carbons, polar protic solvents.

SN2 Reaction

Bimolecular nucleophilic substitution; 1 step: backside attack. Inversion of stereochemistry. Favored by primary carbons, polar aprotic solvents.

E1 Reaction

Unimolecular elimination; 2 steps: carbocation formation then base removes beta-H. Competes with SN1. Favored by heat, weak base.

E2 Reaction

Bimolecular elimination; 1 step: base removes beta-H as leaving group leaves. Requires antiperiplanar geometry. Favored by strong base.

Markovnikov's Rule

In HX addition to alkenes, H adds to carbon with more Hs, X to more substituted carbon.

Zaitsev's Rule

In elimination, the most substituted (stable) alkene is the major product.

Resonance

Delocalization of electrons through pi bonds or lone pairs. Resonance structures differ only in electron placement and stabilize the molecule.

Chirality

A molecule is chiral if it is non-superimposable on its mirror image. Has a stereocenter (carbon with 4 different groups).

Enantiomers

Non-superimposable mirror images. Same physical properties except for optical rotation.

Diastereomers

Stereoisomers that are not mirror images. Different physical and chemical properties.

IR Spectroscopy

Identifies functional groups. OH ~3300 broad, C=O ~1700 sharp, NH ~3300 sharp, C-H ~3000.

NMR Spectroscopy

Shows environment of H atoms. Look for chemical shift (d), splitting (n+1 rule), and integration.

Mass Spectrometry

Identifies molecular weight. M+ peak = molecular ion. Base peak = most stable fragment.

UV-Vis Spectroscopy

Used for conjugated systems. More conjugation = longer wavelength absorption.

Downfield

More deshielded = higher & value (closer to electronegative atoms).

Upfield

Shielded lower d.

IR Active Bonds

Only polar bonds show up in IR. Symmetrical non-polar (e.g. C=C) may be IR-inactive.

pKa Trends

Lower pKa = stronger acid. Resonance and electronegativity stabilize conjugate base.

Inductive Effect

Electron-withdrawing groups stabilize adjacent negative charge, increasing acidity.

Electrophile

Electron-poor species that accepts electrons (Lewis acid).

Nucleophile

Electron-rich species that donates electrons (Lewis base).

Carbocation Stability

3° > 2° > 1° > methyl due to hyperconjugation and resonance stabilization.

Aromaticity

Cyclic, planar, conjugated molecule with 4n+2 pi electrons (Hückel's rule). Example: benzene.

Electrophilic Aromatic Substitution (EAS)

Activators are ortho/para directors. Deactivators are meta directors.

Hydroboration-Oxidation

Anti-Markovnikov, syn addition of H and OH to alkene. Reagents: 1. BH-THF 2. H₂O2, OH-.

Oxymercuration-Demercuration

Markovnikov addition of H and OH to alkene (no rearrangement). Reagents: 1. Hg(OAc)2, H₂O 2. NaBH4.

Epoxide Opening (Acidic Conditions)

Nucleophile attacks more substituted carbon.

Epoxide Opening (Basic Conditions)

Nucleophile attacks less substituted carbon.

Ozonolysis

Cleaves alkenes to carbonyls. Reagents: 03 then Zn/H2O or (CH3)2S.

Diels-Alder Reaction

Cycloaddition between a diene and dienophile → six-membered ring. Stereospecific.

Oxidation of 1° Alcohols

aldehyde carboxylic acid.

Oxidation of 2° Alcohols

ketone

Oxidation of 3° Alcohols

No reaction.

Reduction Reactions

Carbonyls → alcohols using LiAlH4 or NaBH4. LiAlH4 is stronger, reduces more groups.

Grignard Reagents

RMgX; add to carbonyls to form alcohols. Very strong nucleophile.

Aldehyde

Carbonyl on end carbon, more reactive.

Ketone

Carbonyl in chain.

Hyperconjugation

Stabilization from overlap of sigma bonds with empty p-orbitals or π* orbitals.

Hammond Postulate

Transition state resembles the species (reactant or product) closest in energy.

Tautomers

Isomers that interconvert, e.g., keto-enol. Keto usually preferred.

Conjugation

Alternating single/double bonds allow electron delocalization; stabilizes the molecule.

Steric Hindrance

Bulky groups slow down SN2 or E2. SN1/E1 more favored in such cases.

Retrosynthesis

Work backward from target. Identify disconnections that correspond to known reactions.

Functional Group Interconversion

Alcohol → Alkyl Halide (PBг3, SOCI₂); Alkene → Alcohol (acid-catalyzed hydration); Alcohol → Ketone/Aldehyde (oxidation)

Protecting Groups

Temporarily mask reactive groups, e.g., TBDMS for alcohols.

Extraction

Separates based on solubility in aqueous vs. organic layers. Often uses acid/base.

Recrystallization

Purifies solids by exploiting solubility at different temperatures.

Distillation

Separates liquids by boiling points. Fractional distillation used when b.p.s are close.

Thin Layer Chromatography (TLC)

Used to monitor reactions or check purity. Rf = spot distance / solvent distance.

Allylic & Benzylic Positions

Very reactive due to resonance stabilization of intermediates (radicals, carbocations).