Organic Chemistry Exam 3

SN1 and E1 rate formula

Rate = k[substrate]

are SN1 and E1 first order or second order? unimolecular or bimolecular? one or multiple steps

first order / unimolecular / multiple

SN1 steps

loss of leaving group and nucleophilic attack (sometimes also proton transfer to neutralize molecule)

do hydride or methyl shifts occur first

hydride

what is unique about the product of SN1 in terms of writing wedge and dash

can attack from either side so get racemic mixture so can write without a wedge or dash to account for equal amounts of both

what is the intermediate of SN2

carbocation

SN1 reactions done in what solvent?

polar protic

how does increasing substitution of the carbocation intermediate affect the SN1 reaction?

makes it more stable and most reactive

if there is heat or a high temperature, what type of reaction does that favor?

elimination

During E1, what product is the major ALWAYS

most stable

DBN and DBU are what

strong base, weak nucleophile

NaH is what

strong base, weak nucleophile

HO- is what

strong base, strong nucleophile

MeO- and EtO- are what

strong base, strong nucleophile

I-, Br-, Cl- are what

weak base, strong nucleophile

RS- and RSH are what

weak base, strong nucleophile

HS- and H2S are what

weak base, strong nucleophile

H2O is what

weak base, weak nucleophile

MeOH and EtOH are what

weak base, weak nucleophile

strong base, weak nucleophile leads to what reaction at 1, 2, and 3 primary

E2, E2, E2

strong base, strong nucleophile leads to what reaction at 1, 2, and 3 primary

more SN2 and little E2, more E2 and little SN2, only E2

weak base, strong nucleophile leads to what reaction at 1, 2, and 3 primary

SN2, SN2, SN1

weak base, weak nucleophile leads to what reaction at 1, 2, and 3 primary

no reaction (usually), equal SN1 and E1, equal SN1 and E1

why can an SN2 reaction not occur in tertiary with weak base and strong nucleophile

too much steric hindrance prevents backside attack

SN2 reactions occur in what solvent

polar aprotic

common polar protic solvent for SN1 reaction

ethanol

SN2 regio and stereo

alpha carbon substitution / backside attack flips stero

E2 regio and stereo

double bond between alpha and beta carbon, bulky base favors less substituted and small base favors most stable / anti-coplanar hydrogen required

SN1 regio and stereo

alpha carbon substitution but rearrangements possible / mixture of stereoisomers, sp2, flat

E1 regio and stereo

double bond between alpha and beta carbon but most stable alkene always formed as major / less sterically hindered alkene formed

how to determine weak base

pka of conj acid is less than 12

study functional groups and pka

okay

how to treat mesylate, tosylate, and triflate groups

as halogen “X”

what should you do if you have a strong acid with alcohols

protonate base to create good leaving group

monounsaturated vs. polyunsaturated

1 vs. more than 1 double bond

which term gets more important as temperature increases

entropy

two modes of addition

syn (add X and Y from same side) and anti (X and Y added from opposite sides)

hydrohalogenation

add H and X

hydration

add H and OH

hydrogenation

add H and H

halogenation

add X and X

halohydrin formation

add OH and X

first step of hydrohalogenation since we have a strong acid

protonate something

rate determining step of hydrohalogenation and why

first (proton transfer) / double bond is bad base

steps of hydrohalogenation

proton transfer and nucleophilic attack

Markovnikov’s Rule

H added to carbon with more H and halogen added to more substituted carbon

why is H added to less substituted carbon according to Markovnikov

intermediate and transition state are more stable

products of hydrohalogenation stereochemistry

mixture because can attack from either side

what do you need to look for when doing addition reactions

rearrangements

where should positive charge go in rearrangements

on more substituted

catalyst of hydration reaction

acid (use H2SO4 and H2O or just H3O+)

steps of hydration reaction

protonate alkene, water nucleophilic attack, deprotonate to form alcohol

steps of oxymercuration reaction

form a tricylic mercurinium ion, attack with water

are rearrangements possible for oxymercuration reaction

no

steps of hydroboration/oxidation reaction

B from BH3 added to less substituted carbon and H added to more substituted carbon on double bond, OH replaces BH2 using HO- and H2O2

boranes

BH3 and THF, B2H6, 9-BBN

what is on arrow in hydrogenation

H2 and Pt

what type of addition is hydrogenation

syn addition

good at fixing hydrogen

Pd/C

does dissolve in reaction medium, accomplished by using a ligand with the metal

homogenous catalyst

does not dissolve in reaction medium, like Pt or Pd metal

heterogenous catalyst

used in organic synthesis for the homogeneous hydrogenation of alkenes and alkyne

wilkinson’s catalyst

creation of one or two chiral centers results in mixture of

enantiomers

if a chiral catalyst is used, it is possible to synthesize (__) as major

only one enantiomer

if chiral catalyst used, phosphine ligands on wilkinson catalyst replaced with

chiral phosphine ligands

developed a synthesis of L-Dope using a asymmetric hydrogenation as key step

Knowles

showed that chiral ligand BINAP also affords one enantiomer with high selectitiy

Noyori

what kind of addition is halogenation

anti

steps of halogenation mechanism

concerted step where halogen splits and lone pairs bond to carbon on double bond and other side of double bond attacks back to form 3 membered ring, negative charged halogen then does backside attack

steps of halohydrin formation

different sides of double bond attacking halogen and it breaking off, water then attacks, Br- or water then attacks again

what type of addition is halohydrin

anti

in halohydrin formation, halide added to? and OH added to?

less substituted carbon / more substituted carbon

why is halohydrin formation regioselective

water attacks more positive side which leads to more stable intermediate

is the formation of a 3 membered ring always syn or anti

syn

steps of anti-dihydroxylation

syn addition to make 3 membered epoxide using a peroxy acid (MCPBA) and then backside attack with H3O+ , then protonation and deprotonation to get trans diol

oxidizing bazooka

KMnO4

during ozonolysis, if the alkene in a ring, what products?

1 product with 2 carbonyls

during ozonolysis, if alkene not in a ring, what products?

2 products (ketone and aldehyde)

t or f: the total amount of carbons before and after ozonolysis remains the same

t

hydrohalogenation uses (__) why?

peroxide / makes it anti-mark and encourages radical formation