Organic Chemistry Core Concepts: Structured Study Notes

Ch. 2: Alkanes & Cycloalkanes

IUPAC Naming & Cycloalkane Naming

The International Union of Pure and Applied Chemistry (IUPAC) system provides standardized rules for naming organic compounds, including alkanes and cycloalkanes.

• IUPAC Naming: Assigns systematic names based on the longest carbon chain and substituent positions.

• Cycloalkane Naming: Cyclic hydrocarbons are named by adding the prefix 'cyclo-' to the corresponding alkane.

• Example: Cyclohexane, 2-methylpentane.

Axial vs Equatorial Chair Flip

Chair conformations of cyclohexane are crucial for understanding steric interactions and stability.

• Axial Positions: Vertically oriented; more steric hindrance.

• Equatorial Positions: Around the equator; less steric hindrance, more stable for bulky groups.

• Chair Flip: Interconversion swaps axial and equatorial positions.

Newman Projections

Newman projections visualize the spatial arrangement of atoms around a single bond, aiding in the analysis of conformational isomerism.

• Staggered Conformation: Lower energy, atoms are as far apart as possible.

• Eclipsed Conformation: Higher energy, atoms overlap.

• Example: Ethane's staggered vs. eclipsed forms.

Ch. 3: Alkenes & Alkynes

Carbocation Stability

Carbocation stability is central to many organic reaction mechanisms, especially in addition and substitution reactions.

• Order of Stability: Tertiary > Secondary > Primary > Methyl.

• Resonance Stabilization: Carbocations adjacent to double bonds or aromatic rings are stabilized by resonance.

• Example: Allylic and benzylic carbocations.

Alkene Stability

Alkene stability is determined by substitution and conjugation.

• More Substituted Alkenes: Greater stability due to hyperconjugation.

• Trans vs. Cis: Trans alkenes are generally more stable than cis due to less steric strain.

• Example: 2-butene (trans) vs. 2-butene (cis).

Carbocation Intermediate Rearrangements

Carbocation rearrangements occur to form more stable intermediates during reactions.

• Hydride Shift: Movement of a hydrogen atom with its bonding electrons.

• Alkyl Shift: Movement of an alkyl group to stabilize the carbocation.

• Example: 1,2-hydride shift in alkyl halide reactions.

Ch. 4: Addition Reactions

Markovnikov's Rule

Markovnikov's rule predicts the regioselectivity of electrophilic addition to alkenes.

• Rule: The electrophile adds to the carbon with more hydrogens; the nucleophile adds to the more substituted carbon.

• Example: Addition of HBr to propene yields 2-bromopropane.

Hydrohalogenation & Acid-Catalyzed Hydration

These are classic addition reactions to alkenes, following Markovnikov's rule.

• Hydrohalogenation: Addition of HX (HCl, HBr, HI) to alkenes.

• Acid-Catalyzed Hydration: Addition of water in the presence of acid to form alcohols.

• General Equation: $RCH=CH_2 + HX \rightarrow RCHX-CH_3$

Ch. 5: Aromatic Compounds

EAS: Ortho vs. Para Positions & Electron Withdrawing Groups

Electrophilic Aromatic Substitution (EAS) reactions are influenced by substituents on the aromatic ring.

• Ortho/Para Directors: Activating groups direct new substituents to ortho/para positions.

• Electron Withdrawing Groups: Deactivating groups direct to meta positions.

• Example: Nitration of toluene yields ortho and para nitrotoluene.

Electrophilic Aromatic Substitution (Overview)

EAS is the main mechanism for aromatic substitution reactions.

• General Steps: Generation of electrophile, attack on aromatic ring, loss of proton to restore aromaticity.

• Example: Bromination, nitration, sulfonation.

EAS: Halogenation, Nitration, Friedel-Crafts

Specific EAS reactions introduce various functional groups onto aromatic rings.

• Halogenation: Addition of Cl or Br using Lewis acid catalysts.

• Nitration: Addition of NO2 using HNO3/H2SO4.

• Friedel-Crafts: Alkylation or acylation using AlCl3.

Side-Chain Oxidation

Oxidation of alkyl side chains on aromatic rings yields carboxylic acids.

• Example: Oxidation of toluene to benzoic acid.

Aromaticity & Huckel's Rule

Aromatic compounds are cyclic, planar, and follow Huckel's rule for stability.

• Huckel's Rule: Aromatic if the number of π electrons is $4n+2$, where n is an integer.

• Example: Benzene has 6 π electrons ($n=1$).

Ch. 6: Stereochemistry (Chirality)

R and S Configuration

Assigning R/S configuration is essential for understanding chiral centers in molecules.

• Cahn-Ingold-Prelog Rules: Assign priorities to substituents, orient the lowest priority away, and determine the configuration.

• R (Rectus): Clockwise arrangement.

• S (Sinister): Counterclockwise arrangement.

• Example: 2-butanol chiral center.

Meso Compound

Meso compounds contain chiral centers but are achiral due to an internal plane of symmetry.

• Example: Tartaric acid (meso form).

Chirality Test 2: Stereocenter Test

Identifying stereocenters is fundamental for stereochemical analysis.

• Stereocenter: A carbon atom bonded to four different groups.

Ch. 7: Alkyl Halides (SN/E Mechanisms)

SN1, SN2, E1, E2 Chart (Big Daddy Flowchart)

Substitution and elimination reactions of alkyl halides follow distinct mechanisms, summarized in flowcharts.

• SN1: Unimolecular nucleophilic substitution; two-step mechanism, forms carbocation intermediate.

• SN2: Bimolecular nucleophilic substitution; one-step, concerted mechanism.

• E1: Unimolecular elimination; forms carbocation intermediate.

• E2: Bimolecular elimination; one-step, requires strong base.

• General Equations:

  • $RCH_2Br + OH^- \rightarrow RCH_2OH + Br^-$ (SN2)

  • $RCH_2Br + H_2O \rightarrow RCH_2OH + HBr$ (SN1)

  • $RCH_2CH_2Br + OH^- \rightarrow RCH=CH_2 + H_2O + Br^-$ (E2)

Good Leaving Groups, Nucleophiles, and Basicity

The nature of leaving groups and nucleophiles determines reaction rates and mechanisms.

• Good Leaving Groups: Weak bases, e.g., Br-, I-, TsO-.

• Nucleophilicity: Ability to donate electrons; strong nucleophiles favor SN2.

• Basicity: Strong bases favor E2 elimination.

Zaitsev Rule

Zaitsev's rule predicts the major product in elimination reactions.

• Rule: The most substituted alkene is favored.

• Example: Dehydrohalogenation of 2-bromobutane yields 2-butene as the major product.

Ch. 8: Alcohols, Ethers, Acids

Oxidizing and Reducing Agents

Oxidation and reduction reactions are key for transforming alcohols and other functional groups.

• Oxidizing Agents: PCC, KMnO4, CrO3.

• Reducing Agents: NaBH4, LiAlH4.

• Example: Oxidation of primary alcohol to aldehyde.

Leaving Group Conversions: SOCl2 and PBr3

Conversion of alcohols to alkyl halides using SOCl2 or PBr3 is a common synthetic method.

• General Equation: $ROH + SOCl_2 \rightarrow RCl + SO_2 + HCl$

Dehydration Reaction

Dehydration of alcohols forms alkenes via elimination.

• General Equation: $ROH \xrightarrow{H_2SO_4} R=R' + H_2O$

Williamson Ether Synthesis

Williamson synthesis is the main method for preparing ethers.

• General Equation: $R-O^- + R'-X \rightarrow R-O-R' + X^-$

Ch. 9: Acids

Organometallics on Ketones (Grignard Reaction)

Grignard reagents react with ketones and aldehydes to form alcohols, a fundamental reaction in organic synthesis.

• General Equation: $R-MgX + R'CO \rightarrow R'RCOH$

Reducing Agent (NaBH4, LiAlH4)

Reduction of carbonyl groups to alcohols is achieved using hydride donors.

• NaBH4: Reduces aldehydes and ketones.

• LiAlH4: Reduces esters, carboxylic acids, and amides.

Acetal Protecting Group

Acetals are used to protect carbonyl groups during multi-step syntheses.

• Formation: Reaction of aldehyde/ketone with diol under acid catalysis.

Nucleophilic Acyl Substitution (Overview)

Nucleophilic acyl substitution is the central mechanism for carboxylic acid derivatives.

• General Steps: Nucleophile attacks carbonyl carbon, tetrahedral intermediate forms, leaving group departs.

Fischer Esterification

Fischer esterification forms esters from carboxylic acids and alcohols under acidic conditions.

• General Equation: $RCOOH + R'OH \xrightarrow{H^+} RCOOR' + H_2O$

Topic	Main Reaction/Concept	Key Points
Alkanes & Cycloalkanes	IUPAC Naming, Chair Flip	Systematic naming, conformational analysis
Alkenes & Alkynes	Carbocation Stability, Rearrangements	Mechanism, product prediction
Addition Reactions	Markovnikov's Rule, Hydration	Regioselectivity, product formation
Aromatic Compounds	EAS, Aromaticity	Substitution patterns, Huckel's rule
Stereochemistry	R/S Configuration, Meso Compounds	Chirality, symmetry
Alkyl Halides	SN1/SN2/E1/E2	Mechanism, flowchart, product prediction
Alcohols, Ethers, Acids	Oxidation, Reduction, Synthesis	Functional group transformations

Additional info: Some explanations and equations have been expanded for academic completeness and clarity.