unit 3 exam vocab

Activation energy

the minimum amount of energy required to start a chemical reaction

Addition reaction

Two reactants combine to form a single product with no atoms left over.

Bond dissociation energy

energy required to break a covalent bond

Carbocation

An ion that contains a positively charged carbon atom

Electrophile

An electron pair acceptor (electron-poor site)

Elimination reaction

A single reactant splits into two products; essentially the opposite of an addition reaction.

Endergonic

requires/absorbs energy

Endothermic

Absorbs heat

Enthalpy change

heat of reaction, describes the net exchange of energy between the system and its surroundings

Entropy change

the difference between the entropy of the products and the reactants

Exergonic

releases energy

Exothermic

Releases heat

Gibbs free-energy change

determines whether a reaction is spontaneous or requires energy

Heat of reaction

The net change of chemical potential energy of the system

Initiation step

produces radicals (no radicals in reactants, radicals in products)

Nucleophile

An electron pair donor (electron-rich site)

Polar reaction

the reaction between a nucleophile and an electrophile

Propagation step

a radical, the halogen, and the alkane yield alkyl halide product plus more radical to carry on the chain (repeating cycle; radicals in reactants and products)

Radical

a neutral chemical species that contains an odd number of electrons and thus has a single, unpaired electron in one of its orbitals

Radical reaction

Processes that involve symmetrical bond-breaking and bond-making

Reaction coordinate

horizontal axis of reaction diagram

Reaction intermediate

the carbocation, which exists only transiently during the course of the multistep reaction; formed in first step and reacts with ion in second step; indicated by valleys on reaction diagram

Reaction mechanism

An overall description of how a reaction occurs

Rearrangement reaction

One reactant undergoes a reorganization of bonds and atoms to give an isomeric product.

Substitution reaction

Two reactants or components exchange parts to give two new products.

Regiochemistry

where the reaction takes place

Termination step

The final step in a free-radical mechanism in which two free radicals react together to form a molecule

Transition state

the highest-energy structure involved in this step of the reaction; indicated by peaks on reaction diagram; unstable, cannot be isolate

Allylic

the saturated position adjacent to a carbon-carbon double bond

Carbanion

a species containing a negatively charged carbon

Gilman reagent (LiR2Cu)

lithium diorganocopper compounds

Grignard reagent (RMgX)

An organomagnesium halide. (alkyl halide, RX, reacts with Mg to yield alkylmagnesium halides, RMgX)

Organometallic

a compound that contains a carbon-metal bond

Anti periplanar

substituents are attached to parallel bonds on opposite sides of a molecule

Bimolecular

two molecules, nucleophile and alkyl halide, take part in the step whose kinetics are measured; Sn2 and E2 reactions

Deuterium isotope effect

A tool used in mechanistic investigations to establish whether a C-H bond is broken in the rate-limiting step of a reaction.

E2 reaction

a concerted elimination reaction involving a transition state where the base is abstracting a proton at the same time that the leaving group is leaving. The anti-coplanar transition state is generally preferred. Zaitsev orientation is usually preferred unless the base or the leaving group is unusually bulky.

Hoffman (anti-Zaitsev) product

the least substituted alkene formed as the major product during an elimination reaction

Leaving group

Atom or group that departs during a reaction.

Nucleophilic substitution reaction

-SN1 and SN2

-nucleophile forms a bond with a carbon and a leaving group leaves

Periplanar

A conformation in which a hydrogen atom and a leaving group are approximately coplanar.

Rate-determining step

the slowest step in a reaction mechanism

Rate-limiting step

the slowest step in a pathway

Second-order reaction

-rate is proportional to either the concentrations of 2 reactants or to the square of the concentrations of a single reactant

*Rate = k[A]1[B]1 or rate = k [A]2 or

rate = k [B]2

1/([A]) vs time line

slope = k

Sn2 reaction

-bimolecular nucleophilic substitution reactions

- only 1 step (concerted reaction)

-nucleophile attacks the compound at the same time as the leaving group leaves

-Nucleophile actively displaces the leaving group in a backside attack

for this to occur, nucleophile must be strong & substrate can't be sterically hindered

-concentrations of substrate & nucleophile have role in determining the rate --> rate = k[Nu][R-L]

-Position of the substituents around the substrate carbon is inverted

syn periplanar

The H and X atoms can be oriented on the same side of the molecule

Zaitsev's rule / Zaitsev product

In an elimination reaction where more than one alkene product is possible, the major product is the most substituted alkene (the alkene with the greatest number of alkyl substituents attached to the double bond carbon atoms).