Chemistry
Organic Chemistry Reactions Flashcards
39 organic chemistry terms your first mechanism exam assumes you can define
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All 39 Chemistry Organic Chemistry Reactions flashcards
The full deck in writing, listed A to Z. Read it through if the topic is new, then use the cards above to test yourself without looking.
- Anti Addition
- An addition placing the two new groups on opposite faces of a former double bond, typical when a cyclic intermediate blocks one face from further attack.For example: Bromination through a bridged bromonium ion.
- Anti-Periplanar Geometry
- The arrangement E2 requires, with the proton and the leaving group in one plane and 180 degrees apart, so their orbitals line up to become the new pi bond.For example: In cyclohexanes it means both must sit axial.
- Bronsted-Lowry Acid
- A species that donates a proton to another species. Losing that proton converts it into its conjugate base, and how readily it does so is reported as its pKa.For example: Acetic acid donating its hydroxyl proton to water.
- Cahn-Ingold-Prelog Rules
- The priority system for labelling a chirality center. Rank the four groups by atomic number, point the lowest away from you, then read the remaining three as R clockwise or S counterclockwise.For example: Bromine outranks chlorine, which outranks carbon, which outranks hydrogen.
- Carbocation
- A carbon bearing only three bonds and a full positive charge. It is sp2 hybridized and trigonal planar with an empty p orbital, and grows more stable with more alkyl substituents.For example: The tert-butyl cation, stable enough to form in solvolysis reactions.
- Carbocation Rearrangement
- The shift of a neighboring hydrogen or alkyl group, with its bonding electrons, onto a positive carbon to give a more stable cation before the reaction finishes.For example: A secondary cation converting to a tertiary one by a hydride shift.
- Chirality Center
- An atom, usually carbon, bonded to four different groups. Its presence makes a molecule non-superimposable on its mirror image unless internal symmetry cancels it.For example: The central carbon of alanine, bonded to hydrogen, methyl, amino and carboxyl.
- Conjugate Base
- The species that remains after an acid loses a proton. The more its negative charge is spread out or stabilized, the stronger the acid it came from.For example: Acetate, whose charge is shared over two oxygens by resonance.
- Curved Arrow Notation
- The mechanism convention in which each arrow tracks the movement of an electron pair from where the electrons start to where they end up. A single-barbed fishhook shows one electron.For example: An arrow drawn from a lone pair on hydroxide to an electrophilic carbon.
- Diastereomers
- Stereoisomers that are not mirror images of one another. Unlike enantiomers they have genuinely different physical properties, so ordinary methods such as distillation can separate them.For example: Cis and trans 1,2-dimethylcyclohexane.
- E1 Elimination
- A unimolecular elimination in two steps: the leaving group departs to give a carbocation, then a weak base removes a neighboring proton to form the pi bond.For example: Competes with SN1 whenever a carbocation forms in a warm protic solvent.
- E2 Elimination
- A bimolecular elimination in one concerted step: a base removes a proton while the leaving group departs and a pi bond forms. Rate depends on both base and substrate.For example: Sodium ethoxide acting on 2-bromobutane.
- Electrophile
- An electron-poor species that accepts a pair of electrons when a bond forms. It carries a full positive charge, a partial positive atom, or an empty orbital.For example: The carbonyl carbon of acetone, made partly positive by the oxygen.
- Electrophilic Addition
- The characteristic alkene reaction where the electron-rich pi bond attacks an electrophile. The pi bond is destroyed and two new sigma bonds appear across the former double bond.For example: Hydrogen bromide adding across propene.
- Enantiomers
- Two stereoisomers that are non-superimposable mirror images of each other. They share melting point, boiling point and most reactivity, differing in how they rotate polarized light.For example: The two mirror-image forms of 2-butanol.
- Formal Charge
- An electron-bookkeeping value equal to valence electrons minus nonbonding electrons minus half the bonding electrons. It shows which atom carries charge in a Lewis structure.For example: Nitrogen with four bonds and no lone pair carries a formal charge of plus one.
- Functional Group
- A specific group of atoms within a molecule that gives the molecule its characteristic reactivity, so compounds sharing one behave alike regardless of the rest of the skeleton.For example: The hydroxyl group that makes both methanol and cholesterol alcohols.
- Hofmann Product
- The less substituted alkene from an elimination, formed when a bulky base cannot reach the crowded proton Zaitsev's rule would favor and takes an accessible one instead.For example: What potassium tert-butoxide gives where sodium ethoxide gives the Zaitsev alkene.
- Hybridization
- The mixing of atomic orbitals on one atom to give equal-energy hybrid orbitals that match observed geometry. Carbon is sp3 tetrahedral, sp2 trigonal planar, or sp linear.For example: An alkene carbon is sp2 with bond angles near 120 degrees.
- Hydroboration-Oxidation
- A two-stage alkene reaction using borane then basic hydrogen peroxide. It installs an alcohol on the less substituted carbon with hydrogen and hydroxyl adding to the same face.For example: The standard anti-Markovnikov route to a primary alcohol from a terminal alkene.
- Hyperconjugation
- Stabilization gained when a filled neighboring sigma bond overlaps with an empty or partly filled p orbital, spreading electron density into it.For example: The reason a tertiary carbocation outlasts a primary one.
- Inductive Effect
- The pull or push of electron density through sigma bonds caused by electronegativity differences. It weakens sharply with distance and stabilizes nearby opposite charge.For example: The three fluorines of trifluoroacetic acid make it far more acidic than acetic acid.
- Inversion of Configuration
- The stereochemical flip at a carbon when a nucleophile bonds on the face opposite the departing group, turning the other three substituents inside out like an umbrella in wind.For example: Also called Walden inversion, and the reason a single backside attack changes the descriptor.
- Leaving Group
- The fragment that departs from a substrate taking the bonding electron pair with it. The weaker a base it is, the better it leaves, because it holds that charge comfortably.For example: Iodide, water and tosylate leave well; hydroxide and amide leave poorly.
- Lewis Acid
- A species that accepts a pair of electrons to form a new covalent bond, usually because it has an empty orbital or an incomplete octet rather than a proton to give away.For example: Boron trifluoride and aluminum chloride, both used to activate electrophiles.
- Markovnikov's Rule
- When a hydrogen halide adds to an alkene, the hydrogen bonds to the carbon that already carries more hydrogens, because that route passes through the more stable carbocation.For example: HBr and propene giving 2-bromopropane rather than the 1-bromo isomer.
- Nucleophile
- An electron-rich species that donates a lone pair or pi electrons to form a new bond. It is attracted to electron-poor atoms and is usually anionic or bears a lone pair.For example: Hydroxide, cyanide, ammonia and iodide.
- Pi Bond
- A covalent bond formed by side-on overlap of parallel p orbitals, with electron density above and below the bond axis. It is weaker than a sigma bond and locks rotation.For example: The second bond of a C=C double bond, which is why cis and trans alkenes do not interconvert.
- pKa
- The negative base-ten logarithm of the acid dissociation constant. Lower means more acidic, and each whole unit represents a tenfold difference in acid strength.For example: Ethanol sits near 16 while acetic acid sits near 5, so acetic acid is far stronger.
- Polar Aprotic Solvent
- A polar solvent with no hydrogen on oxygen or nitrogen, so it cannot hydrogen bond to anions. It solvates cations while leaving nucleophiles bare and highly reactive.For example: Acetone, DMSO, DMF and acetonitrile.
- Polar Protic Solvent
- A polar solvent bearing a hydrogen on oxygen or nitrogen. It hydrogen bonds to anions, blunting nucleophiles, while stabilizing carbocations and their leaving groups.For example: Water, methanol, ethanol and acetic acid.
- Racemic Mixture
- A sample containing equal amounts of two enantiomers. It shows no net optical rotation because the equal and opposite rotations of the two components cancel.For example: Labelled as plus or minus, or as a fifty-fifty R and S mixture.
- Resonance
- The description of one molecule by two or more Lewis structures that differ only in where electrons sit. The real species is a single delocalized hybrid, not a mixture that flips.For example: The two equivalent structures of a carboxylate anion, which share the negative charge over both oxygens.
- Sigma Bond
- A covalent bond formed by head-on overlap of orbitals along the axis joining two nuclei. Every single bond in a molecule is one of these, and free rotation about it is possible.For example: The C-C bond of ethane, which spins freely at room temperature.
- SN1 Reaction
- A unimolecular substitution in two steps: the leaving group departs first to give a carbocation, which the nucleophile then attacks. Rate depends on substrate concentration alone.For example: Favored by tertiary substrates and weak nucleophiles that double as the solvent.
- SN2 Reaction
- A bimolecular substitution in one concerted step: the nucleophile bonds as the leaving group departs. Rate depends on both partners, and the carbon inverts its configuration.For example: Favored by unhindered primary carbons, strong nucleophiles and polar aprotic solvents.
- Syn Addition
- An addition placing both new groups on the same face of a former double bond, because they are delivered together rather than in separate steps.For example: Catalytic hydrogenation over palladium, and hydroboration.
- Tosylate Group
- A para-toluenesulfonate ester made from an alcohol with tosyl chloride. It converts a hydroxyl, which leaves badly, into an excellent leaving group without touching stereochemistry.For example: Written as OTs and treated in mechanisms much like a bromide.
- Zaitsev's Rule
- The generalization that elimination gives the more substituted alkene as the major product, because extra alkyl groups stabilize the double bond.For example: The trisubstituted alkene forming ahead of the terminal one.