Stereochemistry, Regiochemistry, and Structures

stereoisomers

Compounds with the same structural formula but with a different arrangement of the atoms in space.

mesocompound

A molecule that contains a chiral centre but is achiral (not chiral) as that it has a plane of symmetry.

diastomers

stereoisomers that are not mirror images

Enantiomers

isomers that are mirror images of each other

Constitutional isomers

same molecular formula, different connectivity

gauche conformation

a conformation with a 60 degree angle between the largest groups (methyls)

eclipsed conformation

highest energy no separation. or 120 separation.

Staggard conformation

all far away as possible, most stable

R configuration

clockwise (right)

S configuration

counterclockwise (left)

E configuration

the highest priority groups are on the opposite side of the double bond

Z configuration

the highest priority groups are on the same side of the double bond

Zaitsev's Product

the most substituted alkene product

Hofmann product

when the major product of an elimination reaction is the less substituted alkene

SN1 mechanism

Unimolecular nucleophilic substitution reaction that has two steps

SN2 mechanism

Bimolecular nucleophilic substitution reaction that is one step.

E1 mechanism

Unimolecular elimination involving carbocation formation that is two steps and is never concerted.

E2 mechanism

Bimolecular elimination of a beta molecule occurring in a single step.

Cahn-Ingold-Prelog priority rules

priority is assigned based on the atom bonded to the double bonded carbons, the higher the atomic number the higher the priority

SN1 Reagents

weak nucleophile (HBr, HI, HCl)

SN2 Reagents

strong nucleophile (NaI in acetone) / strong base (OH-)

E1 Reagents

Weak bases (H2SO4, heat)

E2 Reagents

Strong bases (KOH/ EtOH, NaNH2/ NH3, POCl3/ pyridine, NaOCH2CH3)

nucleophile

An electron pair donor

Electrophile

An electron pair acceptor

t-BuOK

strong base, weak nucleophile

Hydrohalogenation (Markovnikov)

H-X

Hydrohalogenation (Anti-Markovnikov)

H-X, ROOR

Acid Catalyzed Hydration

- alkenes to alcohols

- reagents: H20, H+, H2SO4 (aq)

Acid Catalyzed Hydration Regio- and Stereo- selectivity

Markovnikov, no stereoselectivity

Acid Catalyzed Hydration Mechanism

1) protonation of alkene pi bond to form carbocation

2) reaction with H2O to give alcohol product

Hydroboration-Oxidation

-1. BH3, THF 2. H2O2, NaOH

-add OH and H across alkene

-enantiomers are formed

Regio- and Stereoselectivity of Hydroboration-Oxidation

Syn-addition and anti-markovnikov (in addition of H2O)

Hydrogenation

H2, Pt

Bromination

Br2

Regio- and Stereoselectivity of bromination

Anti-addition, Markovnikov

Halohydrin Formation

Br2 and H2O

Gives enantiomer

Syn Dihydroxylation

1. OsO4

2. NaHSO3, H2O

or

1. KMnO4

2. NaOH cold

Ozonolysis

1) O3

2) DMS

Anti Dihydroxylation

1) RCO3H

2) H3O+

Regio- and stereoselectivity of Halohydrin Formation

Markovnikov, anti-addition

Anti Addition Reactions

1. halogenation

2. halohydrin formation

3. modified halohydrin formation

4. oxymercuration-demercuration

5. modified oxymercuration-demercuration

Syn Addition Reactions

1. Peroxyacid Epoxidation

2. Hydroboration/Oxidation

3. Catalytic Hydrogenation

Lindlar's catalyst

alkyne to cis alkene

1st degree substrate

SN2, E2 possible

2nd degree substrate

SN1, SN2, E1, E2 possible

3rd degree substrate

SN1, E1, E2 possible

More pi bonds

more acidity

conjugated diene

double bonds are separated by one single bond

cumulated diene

double bonds are adjacent