Orgo Chem 1: Exam 4 - Alkene and Alkyne Reactions

Ch. 8 and Ch. 9

addition reaction

a reaction involving an increase in the number of groups attached to the alkene and a decrease in the number of elements of unsaturation

anti-addition reaction

an addition reaction in which two groups add to opposite faces of the double bond

electrophilic addition reaction

an addition in which the electrophile (electron-pair acceptor) bonds to one of the double-bonded carbons first, followed by the nucleophile

syn addition reaction

an addition in which two groups add to the same face of the double bond

addition polymer

• a polymer that results from the addition reactions of alkenes, dienes, or other compounds with double and triple bonds

• most addition polymers form by a chain-growth process

alkoxy group

• (alkoxyl group) —> (—O—R)

• an alkyl group bonded through an oxygen atom, as in an ether

alkoxymercuration

• the addition of mercuric acetate to an alkene in an alcohol solution, forming an alkoxymercurial intermediate

• demercuration gives an ether

alkylidene group

• one of the carbon atoms at either end of a double bond, together with its two substituents

• most commonly: =CH2, =CHR, or =CR2

alpha elimination

• the elimination of two atoms or groups from the same carbon atom

• these eliminations can be used to form carbons

beta elimination

• the elimination of two atoms or groups from adjacent carbon atoms

• this is the most common type of elimination

carbene

• a reactive intermediate with a neutral carbon atom having only two bonds and two nonbonding electrons

• the simplest carbene is methylene (:CH2)

chain-growth polymer

• a polymer that results from the rapid addition of one monomer at a time to a growing polymer chain, usually with a reactive intermediate (cation, radical, or anion) at the growing end of the chain

• most of these are addition polymers of alkenes and dienes

demercuration reaction

• the removal of a mercury species from a molecule

• demercuration of the products of oxymercuration and alkoxymercuration is usually accomplished using sodium borohydride (NaBH4)

dihydroxylation reaction

• also known as hydroxylation

• the addition of two hydroxy groups, one at each carbon of the double bond

• formally, an oxidation reaction

epoxide

• also known as an oxirane

• a three-membered cyclic ether

epoxidation reaction

• formation of an epoxide, usually from an alkene

• a peroxyacid is generally used as a reagent

glycol

a 1,2-diol

halogenation reaction

the addition of a halogen (X2) to a molecule, or the free-radical substitution of a halogen for a hydrogen

halohydrin

a beta-haloalcohol, with a halogen and a hydroxy group on adjacent carbon atoms

halonium ion

• a reactive, cationic intermediate with a three-membered ring containing a halogen atom

• usually, a chloronium ion, a bromonium ion, or an iodonium ion

heterogeneous catalysis

the use of a catalyst that is in a separate phase from the reactants

homogeneous catalysis

use of a catalyst that is in the same phase as the reactants

hydration reaction

• the addition of water to a molecule

• the hydration of an alkene forms an alcohol

hydroboration reaction

the addition of borane (BH3) or one of its derivatives (example: BH3 / THF) to a molecule

hydrogenation reaction

• the addition of a hydrogen to a molecule

• the most common hydrogenation is the addition of H2 across a double bond in the presence of a catalyst

  • catalytic hydrogenation or catalytic reduction

Markovnikov’s rule

• when a proton acid adds to the double bond of an alkene, the proton bonds to the carbon atom that already has more hydrogen atoms

• in an electrophilic addition to an alkene, the electrophile adds in such a way as to generate the most stable intermediate

Markovnikov orientation

an orientation of addition that obeys the original statement of Markovnikov’s rule —> gives the Markovnikov product

anti-Markovnikov orientation

an orientation of addition that is the opposite of that predicted by the original statement of Markovnikov’s rule —> gives the anti-Markovnikov product

mCPBA

• (meta-chloroperoxybenzoic acid)

• a common reagent for epoxidizing alkenes

• dissolves in common solvents such as dichloromethane

• as the epoxidation takes place, the m-chlorobenzoic acid by-product precipitates out of solution

metathesis

• also known as olefin metathesis

• any reaction that trades and interchanges the alkylidene groups of an alkene

monomer

one of the small molecules that bond together to form a polymer

organic synthesis

the preparation of desired organic compounds from readily available materials

oxidative cleavage

• the cleavage of a carbon—carbon bond through oxidation

• carbon—carbon double bonds are commonly cleaved by ozonolysis/reduction or by warm, concentrated permanganate (KMnO4)

oxymercuration reaction

the addition of aqueous mercuric acetate to an alkene

ozonolysis reaction

the use of ozone, usually followed by reduction, to cleave a double bond

peroxide effect

• the reversal of orientation of HBr addition to alkenes in the presence of peroxides

• a free-radical mechanism is responsible for this effect

peroxyacid

• also called a peracid

• a carboxylic acid with an extra oxygen atom and a peroxy linkage (—O--O—)

• the general formula is RCO3H

polymer

a high-molecular-weight compound composed of many molecules of a smaller, simpler compound called the monomer

polymerization

the reaction of monomer molecules to form a polymer

regiochemistry

• the orientation of a chemical reaction on an unsymmetrical substrate

• in additions to alkenes, the regiochemistry of the addition involves which part of the reagent adds to which end of an unsymmetrical alkene

regioselective reaction

• a reaction in which one direction of bond-making or bond-breaking occurs preferentially over all other directions

• examples: Addition of HCl (predicted by Markovnikov’s rule); Hydroboration-oxidation (consistently gives anti-Markovnikov orientation

Simmons-Smith reaction

a cyclopropanation of an alkene using the carbenoid reagent generated from diiodomethane and the zinc-copper couple

stereospecific reaction

a reaction that converts different stereoisomers of the starting material into different stereoisomers of the product

acetylene

• the simplest alkyne, H-C=C-H

• also used as a synonym for alkyne, a generic term for a compound containing a C=C triple bond

acetylide ion

• also called an alkynide ion

• the anionic salt of a terminal alkyne

• metal acetylides are organometallic compounds with a metal atom in place of the weakly acidic acetylenic hydrogen of a terminal alkyne

alkoxide ion

R—O(-), the conjugate base of an alcohol

alkyne

• any compound containing a carbon—carbon triple bond

  • a terminal alkyne has a triple bond at the end of a chain, with an acetylenic hydrogen

  • an internal alkyne has the triple bond somewhere other than at the end of the chain

amyl

an older common name for pentyl

enol

• an alcohol with the hydroxy group bonded to a carbon atom of a carbon—carbon double bond

• most are unstable, spontaneously isomerizing to their carbonyl tautomers, called the keto form of the compound

Lindlar’s catalyst

• a heterogeneous catalyst for the hydrogenation of alkynes to cis alkenes

• in its most common form, it consists of a thin coating a palladium on barium sulfate, with quinoline added to decrease the catalytic activity

s-character

• the fraction of a hybrid orbital that corresponds to an s orbit

  • about ½ for sp hybrids, 1/3 for sp2 hybrids, and ¼ for sp3 hybrids

siamyl group

• a contraction for secondary isoamyl, abbreviated “Sia”

• this is the 1,2-dimethylpropyl group

• Example: disiamylborane is used for hydroboration of terminal alkynes, since it is bulky and adds only once to the triple bond

tautomers

• isomers that can quickly interconvert by the movement of a proton (and a double bond) from one site to another

• an equilibrium between these isomers is called a tautomerism

• keto form is more stable than enol form

vinyl cation

• a cation with a positive charge on one of the carbon atoms of a C=C double bond

• the cationic carbon atom is usually sp hybridized

• these types of cations are often generated by the addition of an electrophile to a carbon—carbon triple bond

Electrons always move…

from high concentration to low concentration