Organic

Functional Groups & Reactivity

Priority in Nomenclature (Highest to Lowest)

Hydrocarbon Chemistry

Alkanes (Saturated Hydrocarbons)

• General formula: CₙH₂ₙ₊₂
• Hybridization: sp³
• Bond angle: 109.5°
• Reactions: Halogenation (radical), combustion

CH₄ + Cl₂ → CH₃Cl + HCl (monochlorination)
           ↓ (excess Cl₂)
    CHCl₃ → CCl₄

Alkenes (Unsaturated - C=C)

• General formula: CₙH₂ₙ
• Hybridization: sp²
• Bond angle: 120°
• Reactions: Addition, polymerization, oxidation

Addition Reactions:
┌─────────────────────────────────────────────────┐
│ Electrophilic Addition:                        │
│                                                 │
│   H₂C=CH₂ + HCl → CH₃-CH₂Cl                   │
│   (Markovnikov: H adds to less-substituted C)  │
│                                                 │
│   H₂C=CH₂ + H₂O → CH₃-CH₂OH (acid-catalyzed)  │
│                                                 │
│ Halogen Addition:                               │
│                                                 │
│   H₂C=CH₂ + Br₂ → Br-CH₂-CH₂-Br                │
│   (Anti addition - stereospecific)             │
│                                                 │
│ Hydroboration:                                  │
│                                                 │
│   H₂C=CH₂ + BH₃ → CH₃-CH₂-BH₂                  │
│   → H₂O₂ → CH₃-CH₂OH (Anti-Markovnikov)        │
└─────────────────────────────────────────────────┘

Alkynes (Unsaturated - C≡C)

• General formula: CₙH₂ₙ₊₂
• Hybridization: sp
• Bond angle: 180°
• Reactions: Addition, oxidation, acid-base

Reaction Mechanisms

Nucleophilic Substitution (SN1 and SN2)

# Reaction kinetics conceptual model
class NucleophilicSubstitution:
    """Analyze SN1 vs SN2 reaction factors"""
    
    def predict_mechanism(self, substrate_type, nucleophile, solvent):
        """
        Predict whether SN1 or SN2 is favored
        """
        factors = {
            "substrate": {
                "methyl": "SN2 only",
                "primary": "SN2 favored",
                "secondary": "depends on conditions",
                "tertiary": "SN1 only"
            },
            "nucleophile": {
                "strong": "SN2 (if substrate allows)",
                "weak": "SN1 (if substrate allows)"
            },
            "solvent": {
                "polar_protic": "SN1 favored (solvates nucleophile)",
                "polar_aprolic": "SN2 favored (nucleophile free)"
            }
        }
        
        if substrate_type == "tertiary":
            return "SN1"
        elif substrate_type == "primary":
            return "SN2"
        else:
            return "depends on nucleophile and solvent"
    
    # Steric hindrance calculation
    def steric_hindrance_score(self, substituents):
        """Estimate relative steric hindrance"""
        hindrance = {
            "H": 0,
            "CH3": 1,
            "C2H5": 1.5,
            "iPr": 2,
            "tBu": 3
        }
        return sum(hindrance.get(s, 2) for s in substituents)

Elimination Reactions (E1 and E2)

Stereochemistry

Chirality and Enantiomers

• Chiral center: Tetrahedral carbon with 4 different substituents
• Enantiomers: Non-superimposable mirror images
• Optical activity: Rotate plane-polarized light in opposite directions

R/S Configuration Determination

Priority rules (Cahn-Ingold-Prelog):
1. Higher atomic number = higher priority
2. If tie, check next atoms (I > Br > Cl > S > P > F > O > N > C > H)
3. Double/triple bonds count as multiple atoms

Determination steps:
┌────────────────────────────────────────────────┐
│ 1. Assign priorities (1=highest, 4=lowest)   │
│ 2. View from side opposite lowest priority   │
│ 3. 1→2→3 clockwise = R (Rectus)              │
│ 4. 1→2→3 counterclockwise = S (Sinister)    │
└────────────────────────────────────────────────┘

Geometric Isomers (E/Z)

Conformational Analysis

Butane (CH₃-CH₂-CH₂-CH₃) Newman projections:

Anti (staggered)      Gauche (staggered)     Eclipsed
    H                    CH₃                  H
  /   \                /   \                /   \
 H     H              H     H               H     CH₃
  \   /                \   /                \   /
   C-C                  C-C                   C-C
  /   \                /   \                /   \
CH₃    H              CH₃    H              CH₃    H

Energy: 0 kcal/mol      ~0.9 kcal/mol       ~3.6 kcal/mol

Synthesis Planning

Retrosynthetic Analysis

class Retrosynthesis:
    """Simplified retrosynthetic analysis framework"""
    
    # Common transformations
    TRANSFORMATIONS = {
        "alcohol": {
            "from_alkene": ["hydroboration", "oxymercuration", "acid-catalyzed hydration"],
            "from_carbonyl": ["reduction (NaBH₄, LiAlH₄)", "Grignard addition"],
            "from_ester": ["reduction (DIBAL-H)"]
        },
        "alkene": {
            "from_alkyl_halide": ["elimination (E2/E1)"],
            "from_diol": ["pinacol rearrangement"],
            "from_alkyne": ["partial reduction (H₂/Pd, Lindlar)"]
        },
        "carbonyl": {
            "from_alcohol": ["oxidation (PCC, Jones)"],
            "from_alkene": ["ozonolysis"],
            "from_alkyne": ["hydration (HgSO₄)"]
        },
        "carboxylic_acid": {
            "from_alcohol": ["strong oxidation"],
            "from_ester": ["hydrolysis (acid or base)"],
            "from_nitrile": ["hydrolysis"]
        }
    }
    
    # Synthesis planning
    def plan_synthesis(self, target_functional_group, available_starting_materials):
        """Suggest synthetic route"""
        return self.TRANSFORMATIONS.get(target_functional_group, {})

Common Named Reactions

Molecular Orbital Theory

Frontier Molecular Orbital (FMO) Analysis

HOMO-LUMO Interactions:

Nucleophile (HOMO) → Electrophile (LUMO)
        or
Electrophile (HOMO) → Nucleophile (LUMO)

Orbital symmetry rules govern reaction feasibility:
- Thermally allowed: Symmetry-allowed reactions
- Photochemical: Different symmetry requirements

Conjugation effects:
- Allylic system: 3 p-orbitals → 3 MOs
  - ψ1 (bonding): Both electrons
  - ψ2 (nonbonding): 1 electron
  - ψ3 (antibonding): Empty
  
- Diene: 4 p-orbitals → 4 MOs
  - ψ1, ψ2 (bonding): Filled
  - ψ3*, ψ4* (antibonding): Empty

Pericyclic Reactions

Spectroscopic Methods

IR Spectroscopy (Functional Group Identification)

NMR Chemical Shifts (¹H)

Common Errors to Avoid

1. Confusing SN1/SN2 mechanisms — Always consider substrate structure, nucleophile, and solvent together
2. Ignoring stereochemistry — Label chiral centers and specify R/S in products
3. Forgetting regiochemistry — Markovnikov vs. anti-Markovnikov matters
4. Incorrect IUPAC naming — Follow latest nomenclature rules systematically
5. Over-relying on memorization — Understand mechanisms to predict products
6. Skipping protonation states — Consider pKa in acid-base reactions
7. Ignoring steric effects — Bulky groups affect reactivity significantly
8. Not considering competing reactions — Elimination vs. substitution, etc.