Organic Chemistry
Master the fundamentals of carbon compounds, functional groups, and reaction mechanisms essential for the health sciences.
Organic Reactions
Sign in to track progressUnderstanding common organic reactions helps predict how molecules are formed, transformed, and broken down. Many organic reactions can be understood using one basic idea: electron-rich species attack electron-poor species.
Electrophiles An electrophile is an electron-deficient species that accepts an electron pair to form a new bond.
- "Electron-loving"
- Electron deficient
- Often positive or partially positive
- Accepts an electron pair
- Is attacked by a nucleophile
Common Electrophiles
- H⁺
- CH₃⁺ (carbocation)
- Carbonyl carbon (C=O)
- Alkyl halides, particularly the carbon bonded to the halogen
- BF₃
- AlCl₃
Nucleophiles A nucleophile is an electron-rich species that donates an electron pair to form a new bond.
- "Nucleus-loving"
- Has available lone pairs or π electrons
- Often negatively charged
- Donates an electron pair
- Attacks an electrophile
Many bases can also act as nucleophiles because they have available electron pairs.
Common Nucleophiles
- OH⁻
- CN⁻
- NH₃
- H₂O
- Cl⁻
- Br⁻
- I⁻
- RO⁻ (alkoxide)
- Amines (RNH₂)
Condensation Reactions A condensation reaction joins two molecules with the loss of a small molecule, most often water.
Common examples include:
- Peptide bond formation between amino acids
- Ester formation from a carboxylic acid and an alcohol
Esterification Esterification is a condensation reaction in which a carboxylic acid reacts with an alcohol to form an ester and water.
- Carboxylic acid + Alcohol ⇌ Ester + Water
- Esterification is the reverse of ester hydrolysis
Cleavage Reactions A cleavage reaction breaks one molecule into two or more smaller molecules. Hydrolysis is a common type of cleavage reaction because water is used to break a chemical bond.
Hydrolysis Hydrolysis is a reaction in which water cleaves a chemical bond, splitting one molecule into smaller molecules. It is generally the reverse of condensation.
Examples include:
- Ester + H₂O → Alcohol + Carboxylic acid
- Amide + H₂O → Carboxylic acid + Amine
- Protein + H₂O → Smaller peptides and/or amino acids
- Sucrose + H₂O → Glucose + Fructose
Hydrolysis is important in biological processes such as digestion and also affects the stability of esters and amides in aqueous environments.
Oxidation In organic chemistry, oxidation generally means increasing bonds to oxygen or another electronegative atom, or decreasing bonds to hydrogen.
Common oxidation pathways include:
- Primary alcohol → Aldehyde → Carboxylic acid
- Secondary alcohol → Ketone
Many biological oxidation reactions are carried out by oxidoreductase enzymes.
Oxidizing Agents
PCC (pyridinium chlorochromate)
- Primary alcohol → Aldehyde
- Secondary alcohol → Ketone
- Relatively mild oxidizing agent
- Under typical anhydrous conditions, PCC generally stops oxidation of a primary alcohol at the aldehyde
Reduction Reduction is generally the opposite of oxidation. It involves increasing bonds to hydrogen or decreasing bonds to oxygen.
Common reduction pathways include:
- Aldehyde → Primary alcohol
- Ketone → Secondary alcohol
Reducing Agents
- NaBH₄
- Aldehyde → Primary alcohol
- Ketone → Secondary alcohol
- Commonly considered a mild reducing agent
- LiAlH₄
- Stronger reducing agent
- Aldehyde → Primary alcohol
- Ketone → Secondary alcohol
- Aldehydes and ketones → Alcohols
- Carboxylic acids and esters → Alcohols
Acid-Base Reactions Acid-base reactions involve the transfer of a proton (H⁺) between molecules.
- Brønsted-Lowry acid: donates a proton (H⁺)
- Brønsted-Lowry base: accepts a proton (H⁺)
Carboxylic acids commonly act as acids because they can donate H⁺.
- Carboxylic acid → commonly donates H⁺ → acid
Amines commonly act as bases because the nitrogen has a lone pair that can accept H⁺.
- Amine → commonly accepts H⁺ → base
Key Points
- Electrophiles are electron-poor and accept an electron pair; nucleophiles are electron-rich and donate an electron pair.
- Many bases can act as nucleophiles because they have available electron pairs.
- Condensation reactions join molecules with the loss of a small molecule, often water.
- Esterification combines a carboxylic acid and an alcohol to form an ester and water.
- Hydrolysis is a cleavage reaction that uses water to break chemical bonds.
- Oxidation generally increases bonds to oxygen or decreases bonds to hydrogen; reduction generally does the opposite.
- Primary alcohol → Aldehyde → Carboxylic acid.
- Secondary alcohol → Ketone.
- PCC can oxidize a primary alcohol to an aldehyde or a secondary alcohol to a ketone.
- Aldehyde reduction → Primary alcohol; ketone reduction → Secondary alcohol.
- Carboxylic acids commonly donate H⁺, while amines commonly accept H⁺.