Ranking Radical Stability
1. Benzylic/Allylic Radicals [MOST STABLE] |
2. Tertiary (3°) Radicals |
3. Secondary (2°) Radicals |
4. Primary (1°) Radicals |
5. Methyl Radicals |
Key Factors Affecting Stability:
Resonance Stabilization (Allylic & Benzylic > Non-resonance stablized)
Hyperconjugation
(More alkyl groups donate electron density)
Inductive Effects
(Electron-withdrawing groups destabilize)
Arrow Pushing in Radical Reactions
Fishhook Arrows → movement of 1 electron |
Initiation → arrows depict homolytic cleavage |
Propagation → 1 radical reacts to form another |
Termination → 2 radicals combine to form a stable molecule |
Number of Unique Products
NBS
(Allylic Bromination) |
|
Cl₂/hv
(Radical Chlorination) |
Selective
Only abstracts the allylic hydrogen |
|
Less selective
attacks all possible C-H bonds |
Favors one major product due to resonance stabilization |
|
More radical products due to no preference |
Highly Selective → Major product at most stable radical site |
|
Non-selective → Multiple products |
Synthesis
1. Identify Target Molecule |
Determine functional groups & backbone |
What is the most complex feature? |
2. Work Backward |
Identify possible precursors |
What reactions introduce those functional groups? |
3. Select Key Transformations |
Use known reaction pathways |
Oxidation, Reduction, Substitution, Addition, Elimination |
4. Consider Stereo- & Regio- Chemistry |
Identify selective pathways |
Anti vs Syn, Markovnikov vs Anti-Markovnikov |
5. Check for Side Reactions |
Minimize unwanted byproducts |
Use protecting groups if necessary |
6. Verify Pathway |
Double check feasibility & efficiency |
Are reagents compatible? Do steps make sense? |
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Starting Material → Ether
Name |
Reagents |
Functional Outcome |
Acidic Cleavage |
xsHX (HBr or HI) in heat |
Alkyl Halide |
Oxidation State of Carbons
C-H bond → carbon gains -1 per hydrogen |
C-C bond → no change (0) |
C-X bond → carbon loses +1 per electronegative atom |
The oxidation state of a carbon atom depends on its bonds to atoms of different electronegativities
NMR
1H NMR
|
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13C NMR
|
Chemical Shift Trends |
|
Chemical Shift Trends |
0-2 ppm → Alkane |
|
0-50 ppm → Alkane |
2-3 ppm → Allylic, benzylic, alkynyl |
|
50-100 ppm → Alcohol, ether, alkynes |
4-6 ppm → Alkene |
|
100-150 ppm → Aromatic, alkene |
6-8 ppm → Aromatic |
|
150-200 ppm Carbonyl (ketone, aldehyde, carboxylic acid) |
9-10 ppm →
Aldehyde |
10-12 ppm →
Carboxylic acid (broad) |
Splitting Patterns (n+1 rule)
Singlet → no adjacent protons
Doublet → 1 adjacent proton
Triplet → 2 adjacent protons
IR Spectroscopy
Key Peaks |
O-H (Alcohol) → 3200-3600 cm-1 (broad) |
C-H (Alkanes) → 2800-3000 cm-1 |
C=O (Carbonyls) → ~1700 cm-1 |
C=C (Alkene) → ~1650 cm-1 |
C≡C, C≡N → ~2100-2200 cm-1 |
Terms to Know
Markovnikov's Rule → addition reactions proton added to the carbon with the most hydrogen atoms attached |
Geminal → 2 atoms bonded to the same side of the carbon |
Anti-Markovnivkov's Rule → addition reactions proton added to the carbon with the least hydrogen atoms attached |
Vicinal → 2 atoms bonded to same carbon |
Zaitsev's Rule → elimination reaction, major product is the more stable alkene with the highly substituted double bond |
Syn-Addition → added to same side of compound |
E/Z System → Prioritize the 2 groups attached to each carbon relative to one another.
Higher priority groups are:
cis/same side → Z
trans/opposite sides → E |
Anti-Addition → added to different sides of compounds |
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Formation of Grignard Reagent
Forms Gignard Reagent (RMgX)
Can be used to form C-C bonds
Substitution Reactions
SN1 (Unimolecular) |
|
SN2 (Bimolecular) |
Mechanism → Two-step; carbocation formation, nucleophilic attack |
|
Mechanism → One-step; backside attack |
Rate → Dependent only on substrate
rate=k[R-X] |
|
Rate → Dependent on both substrate & nucleophile
rate=k[R-X][Nu-] |
Stereochemistry → Racemic mixture |
|
Stereochemistry → Inversion of configuration |
Preferred Conditions → Weak nucleophile, polar protic solvent |
|
Preferred Conditions → Strong nucleophile, polar aprotic solvent |
Tertiary > Secondary > Primary |
|
Methyl > Primary > Secondary > Tertiary |
Elimination Reactions
E1 (Unimolecular) |
|
E2 (Bimolecular) |
Mechanism → Two-step; carbocation intermediate, base deprotonates |
|
Mechanism → One-step; concerted β-H abstraction |
Rate → Dependent only on substrate |
|
Rate → Dependent on both substrate and base |
Regiochemistry → Zaitsev's Rule
(more substituted alkene favored) |
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Regiochemistry → Zaitsev's Rule
(unless bulky base → Hofmann product) |
Stereochemistry → Forms most stable alkene |
|
Stereochemistry → Anti-periplanar elimination |
Preferred Conditions → Weak base, polar protic solvent |
|
Preferred Conditions → Strong base required |
Tertiary > Secondary > Primary |
|
Primary > Secondary > Tertiary
(as long as β-H is anti-periplanar) |
Nomenclature
Functional Group |
Suffix (Highest Priority) |
Prefix (Lowest Priority) |
Alcohol (-OH) |
-ol |
hydroxy- |
Alkyne |
-yne |
alkynyl- |
Ether (R-O-R') |
uses parent name |
alkoxy- |
Epoxide |
oxirane (cyclic naming) |
epoxy- |
Key Naming Rules →
Number the longest chain to give OH the lowest number
Number to give triple bond the lowest number, unless -OH is present
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