9701 · 29.2
Characteristic organic reactions flashcards
Revision flashcards for Cambridge 9701 Characteristic organic reactions (syllabus 29.2). Flip, recall, then mark a real past-paper question.
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What is a nucleophile?
An electron pair donor. It is a species with a lone pair of electrons and/or a negative charge, attracted to electron-deficient regions (e.g., a $\delta+$ carbon atom). Examples: OH⁻, CN⁻, NH₃, H₂O.
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What is an electrophile?
An electron pair acceptor. It is a species that is electron-deficient, having a positive charge or a partial positive charge, attracted to electron-rich regions (e.g., a C=C double bond). Examples: H⁺, Br⁺, NO₂⁺.
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What is nucleophilic substitution?
A reaction in which a nucleophile replaces a leaving group (often a halogen) on an atom (usually a saturated carbon). Common with halogenoalkanes.
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What is the difference between SN1 and SN2 mechanisms?
SN1 (Substitution Nucleophilic Unimolecular) is a two-step mechanism via a carbocation intermediate, favoured by tertiary halogenoalkanes. SN2 (Substitution Nucleophilic Bimolecular) is a one-step mechanism with a transition state, favoured by primary halogenoalkanes.
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What is electrophilic addition?
A reaction where an electrophile attacks an electron-rich area (like a C=C bond), breaking the $\pi$-bond and leading to the addition of two groups across the double bond. Characteristic reaction of alkenes.
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State Markovnikov's rule.
When a hydrogen halide (HX) adds to an unsymmetrical alkene, the hydrogen atom adds to the carbon atom of the double bond that is already bonded to the greater number of hydrogen atoms. This forms the more stable carbocation intermediate.
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What is nucleophilic addition?
A reaction where a nucleophile attacks the electrophilic carbon atom of a polar multiple bond (like C=O in carbonyls), breaking the $\pi$-bond. Characteristic reaction of aldehydes and ketones.
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What is a condensation reaction?
A reaction in which two molecules (or parts of the same molecule) combine to form a larger molecule, with the simultaneous loss of a small molecule such as water or ammonia. E.g., esterification, amide formation.
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What is hydrolysis?
The breakdown of a compound by reaction with water. It is the reverse of condensation. For example, an ester is hydrolysed to a carboxylic acid and an alcohol.
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What are the reagents and conditions for the hydration of an alkene?
Reagents: Steam (H₂O(g)). Conditions: High temperature (e.g., 300 °C) and high pressure (e.g., 60 atm), with a concentrated phosphoric(V) acid (H₃PO₄) or sulfuric acid catalyst.
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Why are aldehydes more reactive than ketones towards nucleophiles?
Two reasons: 1. Steric: Aldehydes have a smaller H atom, causing less steric hindrance for the attacking nucleophile. 2. Electronic: Ketones have two electron-donating alkyl groups which reduce the partial positive charge on the carbonyl carbon, making it less electrophilic.