Chemistry: Organic Chemistry Reactions Flashcards

Question 1

Define Sigma Bond.

Accepted Answer

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.

Question 2

Define Pi Bond.

Accepted Answer

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.

Question 3

What is Hybridization?

Accepted Answer

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.

Question 4

What is Resonance?

Accepted Answer

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.

Question 5

Define Formal Charge.

Accepted Answer

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.

Question 6

Define Inductive Effect.

Accepted Answer

The pull or push of electron density through sigma bonds caused by electronegativity differences. It weakens sharply with distance and stabilizes nearby opposite charge.

Question 7

Define Functional Group.

Accepted Answer

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.

Question 8

Define Bronsted-Lowry Acid.

Accepted Answer

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.

Question 9

Define Conjugate Base.

Accepted Answer

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.

Question 10

What is pKa?

Accepted Answer

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.

Question 11

Define Lewis Acid.

Accepted Answer

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.

Question 12

What is Nucleophile?

Accepted Answer

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.

Question 13

What is Electrophile?

Accepted Answer

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.

Question 14

Define Leaving Group.

Accepted Answer

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.

Question 15

Define Tosylate Group.

Accepted Answer

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.

Question 16

What is Carbocation?

Accepted Answer

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.

Question 17

What is Hyperconjugation?

Accepted Answer

Stabilization gained when a filled neighboring sigma bond overlaps with an empty or partly filled p orbital, spreading electron density into it.

Question 18

Define Carbocation Rearrangement.

Accepted Answer

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.

Question 19

Define Curved Arrow Notation.

Accepted Answer

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.

Question 20

Define Chirality Center.

Accepted Answer

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.

Question 21

What is Enantiomers?

Accepted Answer

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.

Question 22

What is Diastereomers?

Accepted Answer

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.

Question 23

Define Racemic Mixture.

Accepted Answer

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.

Question 24

Define Cahn-Ingold-Prelog Rules.

Accepted Answer

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.

Question 25

Define Inversion of Configuration.

Accepted Answer

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.

Question 26

Define SN2 Reaction.

Accepted Answer

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.

Question 27

Define SN1 Reaction.

Accepted Answer

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.

Question 28

Define E2 Elimination.

Accepted Answer

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.

Question 29

Define E1 Elimination.

Accepted Answer

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.

Question 30

Define Anti-Periplanar Geometry.

Accepted Answer

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.

Question 31

Define Zaitsev's Rule.

Accepted Answer

The generalization that elimination gives the more substituted alkene as the major product, because extra alkyl groups stabilize the double bond.

Question 32

Define Hofmann Product.

Accepted Answer

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.

Question 33

Define Polar Aprotic Solvent.

Accepted Answer

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.

Question 34

Define Polar Protic Solvent.

Accepted Answer

A polar solvent bearing a hydrogen on oxygen or nitrogen. It hydrogen bonds to anions, blunting nucleophiles, while stabilizing carbocations and their leaving groups.

Question 35

Define Electrophilic Addition.

Accepted Answer

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.

Question 36

Define Markovnikov's Rule.

Accepted Answer

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.

Question 37

What is Hydroboration-Oxidation?

Accepted Answer

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.

Question 38

Define Syn Addition.

Accepted Answer

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.

Question 39

Define Anti Addition.

Accepted Answer

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.