Organic Chemistry- Chapter 6

Reactions of Alkenes

A reaction in which the C=C pi bond is broken and two new sigma bonds that can form to two new atoms/groups are produced

Addition reaction

What is the most characteristic reaction of alkenes?

Addition reaction

A detailed description of how and why a chemical reaction occurs as it does

Reaction mechanism

An energy minimum between two transitional states

Reactive intermediate

The slowest step in a multistep reaction; the step that crosses the highest energy barrier

Rate-determining step

The most common reactive intermediates involve ________ bonding at a carbon atom

Abnormal

What are three of the most common reactive intermediates?

Carbocations, carbon radicals, and carbanions

(+) charge on a carbon with only 6 valence electrons (3 bonds)

Carbocation

A carbon atom with one unpaired electron

Carbon radical

(-) charge on a carbon with only 3 bonds and one lone pair

Carbanion

The amount of energy required to break a bond into two radicals

Bond dissociation energy

___ can be used to estimate whether a reaction will be exothermic or endothermic

BDE

Are favorable reactions exothermic or endothermic?

Exothermic

Are unfavorable reactions exothermic or endothermic?

Endothermic

A reaction is __________ if the bonds made in the product(s) are stronger than the bonds broken in the reactant(s)

Exothermic

The chemical structures of __________ ______ have essentially no measurable lifetime

Transition states

________ _____________ have distinct measurable lifetimes, but they are extremely short

Reaction intermediates

True or False:

Equilibrium usually favors the side of the reaction with weaker chemical bonds

False

Bond strengths are reported as ____

BDEs

Reactions in which new bonds made in the product(s) are stronger than the bonds broken in the reactant(s) have a _ change in enthalpy

(-)

How do you calculate the change in enthalpy of a reaction?

BDEsr - BDEsp

Electron rich species

Nucleophile

Electron poor species

Electrophile

Electron pair acceptor; electrophile; has at least one empty orbital

Lewis acid

Electron pair donor; nucleophile; has an electron pair

Lewis base

True or False:

The Lewis acid-base definition is very broad

True

True of False:

Bronsted-Lowry bases will commonly be organic functional groups such as alkenes, alcohols, and esters

True

A region of a molecule that is electron rich with a lone pair or a bond

Nucleophile

A region of a molecule that is electron poor (contains a partial (+) charge or a weak bond)

Electrophile

Proton transfers are also known as…

Bronsted-Lowry reactions

Covalent bond formation is also known as…

Combinations of nucleophiles and electrophiles

A dative bond formation is also known as a…

Lewis acid-base reaction

A type of covalent bond where both electrons in the shared pair come from only one of the two atoms

Dative bond

An addition or substitution reaction in which one product is formed in preference to all others that might be formed

Regioselectivity

In the addition of HX, H2O, or ROH to an alkene, H adds to the carbon of the double bond having the greater number of hydrogens

Markovnikov’s Rule

List the following from least stable to most stable:

1. Tertiary carbocation

2. Primary carbocation

3. Methyl cation

4. Secondary carbocation

3, 2, 4, 1

Carbocation stability can be explained by assuming that alkyl groups bonded to a positively charged carbon _______ electron density toward that carbon and help __________ the positive charge on the cation

Release; delocalize

What two types of electron interaction can account for delocalization and carbocation stability?

Inductive effect and hyperconjugation

The polarization of electrons from adjacent sigma bonds to electron deficient areas of a cationic carbon

Inductive effect

Interaction of electrons in a sigma-bonding orbital with the vacant 2p orbital of an adjacent positively charged carbon

Hyperconjugation

The addition of water

Hydration

What is the regioselectivity of an acid-catalyzed hydration reaction?

Markovnikov

Alcohols add to alkenes, forming ______, by the same mechanism as _________

Ethers; Hydration

In electrophilic addition to alkenes, is rearrangement of the carbocation possible?

Yes

Change in connectivity of the atoms in a product compared with the connectivity of the same atoms in the starting material

Rearrangement

True or False:

When rearranging a carbocation, alkyl groups are the only thing that may rearrange

False

When an atom or group of atoms (typically hydrogen or an alkyl group) moves with its bonding electrons from one atom to an adjacent electron-deficient atom

1,2 shift

True or False:

If possible, a carbocation will always rearrange to a more stable one

True

D reacts the same way as what element?

Hydrogen

A reaction carried out in pure reagents; no solvent is used

Neat

A reaction in which one stereoisomer is formed in reference to all others

Stereoselectivity

Stereoselective reactions may be ________________ or __________________

Enantioselective; Diastereoselective

The addition of atoms or groups of atoms to opposite faces of a carbon-carbon double bond

Anti stereoselectivity

What is the stereoselectivity of the addition of Cl2 or Br2?

Anti

True or False:

Water always reacts with alkenes, regardless of the presence or absence of an acid

False

What is the stereoselectivity and regioselectivity of the addition of HOCl and HOBr?

Anti; Markovnikov

Increase in the number of C-Z bonds

Oxidation

Decrease in the number of C-H bonds

Oxidation

Decrease in the number of C-Z bonds

Reduction

Increase in the number of C-H bonds

Reduction

What is the regioselectivity of a oxymercuration-reduction reaction?

Markovnikov

Oxymercuration followed by sodium borohydride reduction results in the _________ of an alkene

Hydration

Does rearrangement occur in oxymercuration-reduction reactions?

No

Does rearrangement occur in acid-catalyzed hydration reactions?

Yes

No carbocation intermediate = no…

Rearranging

What intermediate is present in an oxymercuration-reduction reaction?

Bridged mercurinium ion

True or False:

BH3 = B2H6 = BH3 * THF

True

What is the regioselectivity of a hydroboration-oxidation reaction?

Non-Markovnikov

What is the stereoselectivity of a hydroboration-oxidation reaction?

Syn

_____________-_________ involved the conversion of an alkene to an alcohol

Hydroboration-oxidation

Is rearrangement possible in an acid-catalyzed hydration reaction?

Yes

Acid-catalyzed hydration of alkenes is not _______________

Stereoselective

Is rearrangement possible in a oxymercuration-reduction reaction?

No

What is the stereoselectivity of an oxymercuration-reduction reaction?

Anti

True or False:

Carbocations are not capable of rearranging

False

A reaction in which one stereoisomer is formed in preference to all others that might be formed

Stereoselectivity

The addition of new atoms or groups of atoms from opposite faces of a double bond

Anti addition

In cyclic systems, anti addition =

Trans coplanar addition

Addition of atoms or groups of atoms to the same face of a double bond

Syn addition

A common type of reaction with alkenes in which an electrophilic species adds to a pi bond

Electrophilic addition

Is rearrangement possible for all electrophilic addition reactions?

No

True or False:

HF, HCl, HBr, and HI all add to alkenes to give haloalkanes

False

What are the four elementary steps of mechanisms?

Make a bond; Break a bond; Add a proton; Take a proton away

When in the presence of an acid-catalyst, water converts an alkene into an _______

Alcohol

True or False:

A secondary carbocation would prefer to be a primary carbocation, so it will rearrange to become so

False

True or False:

Rearrangement does not occur with the addition of Br2 or Cl2

True

Cl2 and Br2 in the presence of H2O is used to convert alkenes to ___________

Halohydrins

During the formation of a halohydrin, is a cation intermediate formed? If so, what is the ion called?

Yes; Halonium ion

______________-_________ converts alkenes to alcohols

Oxymercuration-reduction

The addition of mercury (II) to one carbon of the double bond and oxygen to the other

Oxymercuration

True or False:

There is a carbocation intermediate formed in a hydroboration-reduction reaction

False

_____________-_________ is a method of converting alkenes to alcohols

Hydroboration-oxidation

What are the three types of reactions that convert an alkene to an alcohol?

Acid-catalyzed hydration, oxymercuration-reduction, and hydroboration-oxidation