Orgo exam 2

Types of Subsitution runs

1. Concerted = all bonds break/form @ same time

2. Sequential= bonds break and then form in steps

Conserted rxn

all bonds break/form @ same time

-substitution

Sequential rxn

bonds break and then form in steps

-substitution

SN2

• Rate determining step is Nu attack from 180 degree (backside)

• Cause umbrella inversion of stereocenter

• more hindered substrate = slow rxn

• 3* (hindered) @ alpha carbon= no rxn

SN2 with 3* Sterocenter

No rxn w/ 3* substrate

Alpha carbon type EFFECT on SN2 speed

1*= Fastest

4*= slowest

-More hindered= slower

Détermine Nu strength of SAME ATOM

stronger base (use CA pka) = stronger Nu

Stronger nucleophile reacts ____

Stronger nucleophile reacts Faster

Determine Nu strength of DIFFRENT atoms

PROTIC solvent—> less EN= STRONG Nu

APROTIC solvent—> MORE basic= STRONG Nu

Charged Nu are ____ than neutral Nu

Charged Nu are STRONGER than neutral Nu

Leaving group strength

Weaker base= GOOD LG

Rx is abbrev. for _____

Substrate

Sn2 rate law

Rate= k[Nu][RX]

Sn1 rate law

Rate= k[RX]

Sn2 substrate trend

Less hindered = faster rxn

Sn1 substrate trend

stable carbocations = faster rxn

Sn2 nucleophile trend

STRONG Nu favored

Stronger Nu=faster rxn

Sn1 nucleophile trend

WEAK Nu favored

Weak nu = faster rxn

Sn2 steriochemical outcome

100% inversion of sterocenter

SN1 stereochemical outcome

Racemization of stereocenter

Wedges & shoes —> lines

Sn2 solvent trend

Favor polar APROTIC solvent

APROTIC= faster rxn

Sn1 solvent trend

Favor PROTIC solvents

PROTIC= faster rxn

3* alpha carbon rxn possibilities

SN1, E2 & E1

• SB Nu = E2

• WB neutral Nu = SN1 & E1 (@ high temp)

1* alpha carbon rxn possibilities

Sn2 & E2

-mainly Sn2

-E2 ONLY hindered by SB nucleophile

2* alpha carbon rxn possibilities

SN2, SN1, E2 & E1

• SB Nu = E2

• WB negative Nu & APROTIC = SN2

• WB neutral Nu = SN1 & E1 (@ high temp)

Strong BASIC Nu

H2N-

(CH3)CO-

CH3CH2O-

CH3O-

RO-

HO-

STRONG WB Nu

CH3S-

HS-

N=_C-

I-

Br-

Cl-

H3N:

CH3COO-

RCOO-

Weak Nu (neutral)

H2O

CH3OH

ROH

APROTIC solvents

Acetone

DMF

DMSO

acetonitrile (CH3C=_N)

THF

Steps to determine faster rxn

1. Substrate structure (1*> 2*>etc.)

2. Nu type (strong WB Nu, SB Nu, etc.)

3. Leaving group (good/bad)

4. Solvent type

What causes Magnetically active

Nuclei w/ ODD # protons or neutrons

NMR spectra characteristics

1. # signals= # chemical environments

2. Chemical shift

3. Integration ( Area under curve)

4. Multiplicity of signals (signals)

Number of signals

Chem equivalent protons resonate @ same frequency

Chemical shift

Resonance frequency relative to TMS standard

Integration

H ration

Multiplicity of signals

Signal splits into n+1

n= # adjacent EQUIVALENT H

Enthalpy (H)

pos(+) =endothermic

Neg(-) =exothermic

Entropy (S)

Measure of disorder & # of states can occupy

Ring structure ENTROPY(S) is ____ because of ______

Entropy=less DUE TO LIMIT ROTATION

Exergonic G sign

neg(-) G

Endergonic G sign

Pos(+) G

Rxn type w/ K>1

Exergonic (-G)

Rxn type K<1

Endergonic (+G)

Exergonic energy chart

Reactants HIGHER than products

K>1

Endergonic energy chart

Reactants LOWER than products

K<1

Ea activation energy

Distance btwn reactants & peak

Transition state

Peaks on graph

E2 Zaitsev

E2 w/ Small bases = major confirmation

E2 Hofmann

E2 w/ Large base= Minor

E2 large bases example

tBu-

(£t)3CO-

LDA