OCHEM quiz 2

constitutional isomers

different bonds

stereoisomers

same bonds, different arrangement in 3D space

conformational isomers

stereoisomers that cannot be separated, ie. C-C single bond rotation

configurational isomers

stereoisomers that can be separated (E/Z, cis/trans, R/S)

geometric isomers

cis/trans and E/Z

chiral center

an sp3 atom bonded to 4 distinct groups

stereocenters

sp3 chiral centers or E/Z sp2 carbons where swapping two groups changes the label

optically active

has chiral centers and rotates plane polarized light

optically inactive

no chiral centers OR chiral centers that cancel out

meso compound

two identical but opposite chiral centers, so that rotation of plane polarized light cancels out

max number of stereoisomers

2^(number of chiral centers)

diastereomers

stereoisomers whose bonds are not directly opposite

enantiomers

stereoisomers where chiral centers are exactly opposite (dashes and wedges)

cis/trans

used for cyclic compounds to denote if substituents are on the same or different sides of the plane

+ and - optical activity

(+) rotates plane polarized light clockwise

(-) rotates plane polarized light counterclockwise

if one enantiomer is (+), the other is (-) and the same amount

enantiomeric excess

the excess of one enantiomer causes its light rotation to affect the compound overall

ee equation

ee = (observed specific rotation)/(actual rotation of pure enantiomer) * 100%. ee is the enantiomer in excess

degrees of unsaturation

((2*Cs + 2) - total H’s )/2

what features are degrees of unsaturation

multiple bonds and rings

electrophile

seeks electrons

nucleophile

provides electrons

thermodynamics

how much product is formed

kinetics

how fast does a reaction occur

exergonic

reactant energy is higher than product energy

endergonic

product energy is higher than reactant energy

delta g (double dagger)

initial activation energy barrier

entropy

freedom of motion

factors that influence reaction rate

• the frequency of collisions

• the proportion of collisions that have enough energy to react

• the proportion of collisions that are correctly oriented

speeding up a reaction

• add more reactants

• increase the temperature

• add a catalyst

intermediate

compound formed between steps of a reaction

rate limiting step

whatever step has the HIGHEST ENERGY transition state

how catalysts can work

• form a more reactive reactant

• form a lower energy transition state

• provide a different mechanism/intermediate

regioselectivity

the preferential formation of one constitutional isomer over another

markovnikov’s rule

the nucleophile will attach to the MORE substituted sp2 carbon

hydration reaction

1. H2SO4 catalyst removes a proton from water, becoming H3O+

2. double bond attacks a H+ from H3O+, attaching to the less substituted carbon, and forming a carbocation on the more substituted carbon

3. H2O attacks the carbocation, becoming H2O+

4. H2O deprotonates the H2O+ substituent, leaving OH, and remaking the H3O+ catalyst

carbocation rearrangement

if an adjacent carbon is more substituted, carbocation will switch with H- or CH3- to become more stable

addition of an alcohol to an alkene

1. double bond attacks a H+ from alcohol, attaching to the less substituted carbon, and forming a carbocation on the more substituted carbon

1. H2O attacks the carbocation, becoming H2O+

2. H2O deprotonates the H2O+ substituent, leaving OH, and remaking the H3O+ catalyst

HSO4-

byproduct of H2SO4 protonating water or an alcohol, that plays no role in the reaction, but allows the extra H+ from H2O or alcohol to act as an electrophile

rate determining step in alcohol/hydration reactions

the “first step”, where the double bond breaks and H+ attaches as an electrophile

H2SO4

catalyst strong acid used in addition of alcohols and water to alkenes, works by protonating them

Hydroboration oxidation

concerted reaction in which BH3 or 9-BBN adds as an electrophile to the less substituted carbon, and then from solution, is replaced by to an H2O+, and from solution, reduced into an OH group

oxidation reaction

decreases the number of C-H bonds, making the molecule more complex

reduction reaction

increases the number of C-H bonds, making the molecule more rudimentary

Reactions with Halogens (non-nucleophilic solvent)

If the solvent is non-nucleophilic, the two halide ions will attach across the double bond (vicinal)

Reactions with Halogens (non-nucleophilic solvent) steps

1. the double bond attacks the dihalide, taking an electrophile into a 3 membered ring, forming a bromonium or chloride ion with a positive charge

2. the negatively charged, free floating bromide ion attacks the bromonium ion, so each is attached to one side of the double bond

Reactions with Halogens (H2O solvent)

Forms a halohydrin

Reactions with Halogens (H2O solvent) steps

1. he double bond attacks the dihalide, taking an electrophile into a 3 membered ring, forming a bromonium or chloride ion with a positive charge

2. H2O from the solvent attacks the bromonium ion, attaching to the more substituted carbon, and carrying a positive charge

3. H2O from the solvent deprotonates the substituent, leaving a neutral OH group

halogens with other nucleophiles

First one halogen cation will add as an electrophile to the less substituted carbon, then the next halogen or H2O group will add as a nucleophile to the more substituted carbon

Epoxidation Reactions

starts with a peroxyacid, and ends with an epoxide and a carboxylic acid

mechanism for epoxidation

double bond of an alkene attacks the electrophilic H at the end of the peroxyacid, and the electrons shuffle through the molecule to the double bonded oxygen, where they attack the other carbon of the double bond as a nucleophile

mCPBA

acid of choice for epoxidation

Epoxidation Reduction

1. mCPBA converts the alkene into an epoxide

2. LAH provides a hydrogen with its lone pair to remove one double bond, leaving O- attached to the more substituted carbon

3. H+ from solution binds to O- making neutral OH

no carbocation forms, so there is no rearrangement

carbene

carbon with a lone pair (neutral)

addition of a carbene to an alkene

double bond attacks the carbene, and carbene attacks the electrophilic carbon as a nucleophile, forming a 3 membered ring (concerted)

forming a carbene

simmons smith reaction

Zn(Cu) and CH2I2 attach another carbon to a double bond, creating a 3 membered ring

ozonolysis

at -78*C, (CH3)2S can cleave a double bond and attach Oxygen to the ends

ketone

double bond to O within the molecule

aldehyde

double bond with O at the end of the molecule, so that the carbon is attached to R group, O and an H

hydrogenation reaction

H2 is added across the double bond with Pd/C (on the same side)

alkene stability

more stable the more alkyl substituents are coming off of it

predicting alkene stability

1. the most stable carbocation will form first

2. if there is a tie, the least stable alkene will react first