oat orgo unit 4

they call me runny poop the way i trickle down your legs

nucleophile

attracted to positively charged or electron deficient species and likely have a partial negative charge.

nucleophile examples

electrophile

attracted to electrons and likely have a partial positive charge.

electrophiles examples

common leaving groups

nucleophilicity

the rate at which nucleophiles donate a pair of electrons to an electrophile.

polar protic solvent

has hydrogens attached to O or N atoms, allowing them to form hydrogen bonds

larger ions make better nucleophiles

polar aprotic solvent

has polar bonds, but no bonds between H and O/N.

Smaller ions are better nucleophiles.

nucleophilicity factors

• Increases when the anion (nucleophile) is less stable

• Polar aprotic solvent reactivity: C > N > O > F > Cl > Br > I

• Polar protic solvent reactivity: C > N > O > F and I > Br > Cl > F

SN2 process

• Nucleophile attacks electrophile and leaving group leaves at the same time.

• Electrophile always has four atoms bonded to it, and at least one must be hydrogen.

• Rate law equation: Rate = k[Nuc][Elec] ← BIMOLECULAR

• There is a pentavalent transition state.

• Concerted reaction: all bond breaking and forming occurs during the same step.

SN2 reaction mechanism

SN2 arrows

SN1 process

• Step 1: Leaving group leaves electrophile (rate limiting step)

• Step 2: Carbocation rearrangement if possible (moving (+) to more stable position.

• Step 3: Nucleophile later attacks electrophile.

• Rate law equation: Rate = k[Elec] ← UNIMOLECULAR

• Multistep reaction with a carbocation intermediate.

• Can only happen with secondary or tertiary substrates (primary is too unstable)

carbocation stability

SN1 reaction mechanism

• Nucleophile will attack either the front or back of electrophile.

• If electrophile is chiral, there will be a racemic mixture.

Elimination reactions

always result in alkene or pi bond products, caused by a leaving group and a hydrogen leaving a molecule.

Hofmann vs Zaitsev product

• Zaitsev = more substituted alkene & more stable; only for small, nonsterically hindered bases

• Hofmann = less substituted alkene & less stable; only for large, sterically hindered bases.

alkene stability

more substituted = more stable

E2 reaction properties

• Bimolecular rate law: Rate = k[Base][Elec]

• LG and Beta proton have to be antiperiplanar (pointed opposite directions)

• Concerted reaction (1 step)

• Cyclic: LG and BP must also be axial.

• Stereoselectivity: E product is favored due to less steric hindrance, but Z is still possible.

E2 stereoselectivity

• Draw Newman projection on potential pi bond.

• Rotate a single bond to have the LG and BP in antiperiplanar positioning.

• Replace LG and BP with double bond, and draw final product (with rotated bonds taken into account)

E2 mechanism arrows

E1 reaction properties

• LG leaves, making a carbocation intermediate. Then, a base takes off a hydrogen to make a double bond.

• There can be carbocation rearrangements, which makes the reaction faster.

• Unimolecular rate law: Rate = k[Elec]

E1 carbocation rearrangement

E1 and E2 differences

• E2 favors strong bases, E1 favors weak bases

• E2: LG and BP must be antiperiplanar

• E1: Carbocation is formed

Heat

will favor E1 reactions over SN1 reactions.

acid catalyzed dehydration of alcohols

must have a strong acid and an alcohol.

• Acid protonates alcohol, making H₂O⁺-R (good LG)

• Next, E1 reaction happens if 2^o or 3^o, E2 if 1^o.

• Gives both Zaitsev (major) and Hofmann (minor) products.

hydride shift

Hydrogen swaps with a neighboring carbocation to stabilize the carbocation.

methyl shift

Methyl swaps with a neighboring carbocation to stabilize the carbocation.

reaction mechanism factors

• Degree of substitution of substrates

• Strength of Base/Nucleophile

• Steric Hindrance of Base/Nucleophile

• Solvent Effects

• Temperature

substrate substitution for determining mechanism

• Primary - SN2 and E2 are possible. SN1 and E1 are not because primary carbocations are too unstable.

• Secondary - All SN and E mechanisms.

• Tertiary - SN1, E1, and E2 are possible. SN2 is not possible due to steric hindrance.

Base/nucleophile strength for determining mechanism

• Nucleophiles are used in substitution, while bases are used in eliminations (attacking electrophilic carbon vs removing a proton)

• Negatively charged = strong base/nucleophile = SN2 and E2 are favored.

• Neutral charge = weak base/nucleophile = SN1 and E1 are favored.

• Steric hindrance = acts as a base and E2 is favored.

solvent effects for determining reaction mechanism

• Polar protic solvent - stabilizes carbocation intermediate

• Polar aprotic solvent - doesn’t hydrogen bond, so no interaction.

mechanism flow chart

regiochemical and stereochemical chart

alcohol reactions

• Alcohol + Hydrohalic acid = SN1 or SN2

• Alcohol + Concentrated acid + heat = E1 or E2

  • 2^o or 3^o = E1 = Zaitsev

  • 1^o = E2

fart

elimination of a methane out of my butt molecule