Flashcards · 9701 · AS Topic 13

An introduction to AS Level organic chemistry (AS Level) flashcards

21 cards on AS Topic 13, subtopics 13.1 to 13.4. Pick a subtopic or study them all.

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Structural, displayed and skeletal formulae: Structural: the arrangement written on one line, e.g. CH₃CH₂OH. Displayed: every atom and every bond drawn. Skeletal: the carbon backbone as lines; carbons and their hydrogens implied.
What is implied at each vertex and line end of a skeletal formula?: A carbon atom, with enough hydrogens to make four bonds.
The three parts of a systematic name: Root: the longest continuous carbon chain. Suffix: the principal functional group. Prefix: substituents, in alphabetical order. Number from the end that gives the principal group the lowest locant.
Homologous series: A family of compounds with the same functional group and general formula, differing by CH₂, with similar chemical properties and a gradual trend in physical properties.
Name CH₃CH(OH)CH₂CH₃: Butan-2-ol (four-carbon chain, OH on carbon 2).

Addition, substitution and elimination reactions: Addition: two reactants become one product. Substitution: one atom or group replaces another. Elimination: a small molecule is lost, usually forming a double bond.
Hydrolysis and condensation reactions: Hydrolysis: breakdown by reaction with water. Condensation: two molecules join with loss of a small molecule, often water.
Homolytic and heterolytic fission: Homolytic: the bond breaks evenly, one electron to each atom, forming two radicals (half-arrows). Heterolytic: one atom takes both electrons, forming a cation and an anion (full curly arrows).
Nucleophile and electrophile: Nucleophile: an electron-pair donor, attracted to δ+ atoms. Electrophile: an electron-pair acceptor, attracted to δ− regions.
Rules for curly arrows: A full arrow moves a pair of electrons, a half-arrow one electron. It starts from a bond or a lone pair (never an atom or a charge) and ends where the electrons go. Charges must balance.
Match the mechanism to its substrate: free-radical substitution, electrophilic addition, nucleophilic substitution, nucleophilic addition: Free-radical substitution: alkanes + halogen, UV. Electrophilic addition: alkenes. Nucleophilic substitution: halogenoalkanes. Nucleophilic addition: aldehydes and ketones.

Shape around sp³, sp² and sp carbon atoms: sp³: tetrahedral, 109.5°. sp²: trigonal planar, 120°. sp: linear, 180°.
Why is ethene planar?: Both carbons are sp² hybridised, so all six atoms lie in one plane. The unhybridised p orbitals overlap sideways above and below this plane to form the π bond.
Why is the π bond in C=C weaker and more reactive than the σ bond?: Sideways overlap of p orbitals is less effective than head-on overlap, and the π electron density lies above and below the plane, exposed to electrophiles.
Number of σ and π bonds in a C=C double bond and in a C≡C triple bond: C=C: one σ + one π. C≡C: one σ + two π.

Structural isomers: Compounds with the same molecular formula but a different structural formula (different connectivity).
Chain, position and functional group isomerism (one example each): Chain: different carbon skeleton (butane / methylpropane). Position: same group, different place (propan-1-ol / propan-2-ol). Functional group: different group (propanal / propanone).
Two conditions for cis–trans (geometrical) isomerism: A C=C double bond, which prevents rotation, and two different groups on each carbon of the double bond.
Chiral centre and optical isomers: A chiral centre is a carbon atom with four different groups attached. It gives two optical isomers (enantiomers): non-superimposable mirror images that rotate plane-polarised light in opposite directions.
Why is a racemic mixture optically inactive?: It contains equal amounts of the two enantiomers, which rotate plane-polarised light equally in opposite directions, so the effects cancel.
Stereoisomers: Compounds with the same structural formula (same connectivity) but a different arrangement of atoms in space: cis–trans and optical isomers.