alkenes

addition

is the opposite of elimination. A pi bond will often act as a lewis base (as nucleophile or as a bronsted lowry base)

low temperature

the entropy is small and thalpy term dominates -G will be negative K>1 products are favored

high temperature

the entropy term is large, and the entropy term dominates, -G will be reactants are favored K<1

pi bond

areas of electron density, nucleophile and base

equilibrium

elimination and addition are in _________ w/each other

reagents

are acids or electrophiles

temperature dependent

ehtalpy is favored adn entropy is not. high temp = elimination low = addition

hydrohalogenation

addition of H and X. 1 reaction

hydrohalogenation

the reaction of alkenes with HX (where X= Cl, Br, I) in which H and X are added across the pi bond

symmetrical alkene

it does not matter so much that new groups are added

low

____ temperature favors addition reaction

four things to consider:

• mechanism

• regiochemistry

• stereochemistry

• carbocation rearrangements

hydrohalogenation mechanism

1. carbocation generation via proton transfer (rate determining step)

2. nucleophilic attack

more

the _____ stable carbocation forms on a pi bond. the key intermediate is a carbocation

regioselectivity (hydrogenation)

markonikovs rule

markovnikovs rule

H atoms tend to add to the carbon already bearing more H atoms. no minor products formed

smaller Ea

for more substituted formation of cabrocation

hyperconjugation

the positive charge that is forming is stabilized by ___________ from more substituted carbon

flat

when a new chiral center is formed, there are two possible Markovnikov products because the carbocation is _____, meaning it can be attacked from either side

racemic mixture

chiral center formed

rearrangements

(via hydrogen or alkyl shifts) will occur if they can form a more stable carbocation. This leads to a mixture of products which limits synthetic utility

major product

comes from the most stable carbocation

hydration

adds H2O across pi bond. addition of H and OH. 3 reactions

three methods of alkene hydration

1. acid catalyzed hydration

2. oxymercuation demecuration

3. hydroboration-oxidation

acid catalyzed hydration

• regiochemistry: markovikov addition

• stereochemistry: racemic mixture of products

• rearrangements: possible

• carbocation intermediate

oxymercuation-demercuration

• regiochemistry: markovnikov addition

• stereochemistry: anti addition

• rearrangements: not possible

• cyclic intermediate

hydroboration-oxidation

• regiochemistry: anti-markovnikov addition

• stereochemistry: syn addition

• rearrangements: not possible

• concerted reaction so no intermediate

hydration reagent

H3O+ (strong acid) or dilute H2SO4, H2SO4, and H2O

racemic

due to carbocation intermediate, rearrangemnts are possible, we observe the Markovnikoc product as the major product and new chiral centers produce a ________ mixture of enatiomers

steps of hydration

proton transfer from alkene, then nucleophilic attack then proton transfer to neutralize if it has a charge

equilibrium

similar to hydrohalogenaton, hydration reactions are also at __________ between an alkene and an addition product

low temp

favors addition product

dilute H2SO4 and water

favors addition product