Organic Chemistry: Types of Reactions

Overview

Focus on four main types of reactions in organic chemistry:
- Addition Reactions: Involves adding atoms to a molecule, typically across a double or triple bond.
- Elimination Reactions: Involves removing atoms from a molecule, often forming a double bond.
- Substitution Reactions: Involves replacing one atom or group with another.
- Rearrangement Reactions: Involves structural rearrangement within the molecule to form a more stable structure.

Example: Converting an alkene to an alkane by adding hydrogen gas across a double bond using a metal catalyst.
Electrophilic Addition: Adding an electrophile to an alkene, like HBr to 1-butene to form 2-bromobutane.
Nucleophilic Addition: Adding a nucleophile, e.g., converting a ketone to an alcohol using sodium borohydride.

Example: Dehydration of 2-butanol with sulfuric acid to form an alkene.
E1 Reaction: Involves the formation of a carbocation and then removal of a proton to form a double bond, e.g., forming an alkene from an alcohol.
E2 Reaction: A concerted reaction mechanism with strong bases, forming double bonds without carbocation intermediates.
E1CB Reaction: Involves elimination of a poor leaving group, forming unsaturated ketones.

SN1 Reaction: Involves carbocation formation and nucleophilic attack, e.g., tert-butyl bromide with methanol.
SN2 Reaction: A one-step reaction where a nucleophile attacks from the back, e.g., hydroxide with 1-bromobutane.
Free Radical Substitution: Involves radicals, e.g., bromination of alkanes in the presence of UV light.
Electrophilic Aromatic Substitution (EAS): Substitution on aromatic rings, e.g., nitration of benzene.
Nucleophilic Aromatic Substitution: Involves nucleophiles replacing leaving groups on aromatic rings, e.g., forming para-nitrophenol.

Carbocation Rearrangement: Secondary rearranges to tertiary carbocations for stability.
Hydride Shift and Methyl Shift: Movement of hydride or methyl groups to form more stable carbocations.
Ring Expansion: A smaller ring expands to a larger, more stable ring, often from 5 to 6 carbons.

Addition Examples: Reaction mechanisms for electrophilic and nucleophilic additions.
Elimination Examples: Mechanisms for E1, E2, and E1CB reactions.
Substitution Examples: Mechanisms for SN1 and SN2 reactions, and free radical substitutions.
Rearrangement Examples: Understanding hydride/methyl shifts and ring expansions.

Mastery of the four main types of reactions is crucial for success in organic chemistry.
Variations within these categories include electrophilic and nucleophilic types of addition and substitution reactions.

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