Orgo exam 2

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Types of Subsitution runs

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50 Terms

1

Types of Subsitution runs

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

  2. Sequential= bonds break and then form in steps

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2

Conserted rxn

all bonds break/form @ same time

-substitution

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3

Sequential rxn

bonds break and then form in steps

-substitution

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4

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

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5

SN2 with 3* Sterocenter

No rxn w/ 3* substrate

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6

Alpha carbon type EFFECT on SN2 speed

1*= Fastest

4*= slowest

-More hindered= slower

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7

DĂ©termine Nu strength of SAME ATOM

stronger base (use CA pka) = stronger Nu

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8

Stronger nucleophile reacts ____

Stronger nucleophile reacts Faster

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9

Determine Nu strength of DIFFRENT atoms

PROTIC solvent—> less EN= STRONG Nu

APROTIC solvent—> MORE basic= STRONG Nu

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10

Charged Nu are ____ than neutral Nu

Charged Nu are STRONGER than neutral Nu

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11

Leaving group strength

Weaker base= GOOD LG

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12

Rx is abbrev. for _____

Substrate

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13

Sn2 rate law

Rate= k[Nu][RX]

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14

Sn1 rate law

Rate= k[RX]

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15

Sn2 substrate trend

Less hindered = faster rxn

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16

Sn1 substrate trend

stable carbocations = faster rxn

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17

Sn2 nucleophile trend

STRONG Nu favored

Stronger Nu=faster rxn

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18

Sn1 nucleophile trend

WEAK Nu favored

Weak nu = faster rxn

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19

Sn2 steriochemical outcome

100% inversion of sterocenter

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20

SN1 stereochemical outcome

Racemization of stereocenter

Wedges & shoes —> lines

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21

Sn2 solvent trend

Favor polar APROTIC solvent

APROTIC= faster rxn

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22

Sn1 solvent trend

Favor PROTIC solvents

PROTIC= faster rxn

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23

3* alpha carbon rxn possibilities

SN1, E2 & E1

  • SB Nu = E2

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

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24

1* alpha carbon rxn possibilities

Sn2 & E2

-mainly Sn2

-E2 ONLY hindered by SB nucleophile

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25

2* alpha carbon rxn possibilities

SN2, SN1, E2 & E1

  • SB Nu = E2

  • WB negative Nu & APROTIC = SN2

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

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26

Strong BASIC Nu

H2N-

(CH3)CO-

CH3CH2O-

CH3O-

RO-

HO-

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27

STRONG WB Nu

CH3S-

HS-

N=_C-

I-

Br-

Cl-

H3N:

CH3COO-

RCOO-

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28

Weak Nu (neutral)

H2O

CH3OH

ROH

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29

APROTIC solvents

Acetone

DMF

DMSO

acetonitrile (CH3C=_N)

THF

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30

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

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31

What causes Magnetically active

Nuclei w/ ODD # protons or neutrons

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32

NMR spectra characteristics

  1. # signals= # chemical environments

  2. Chemical shift

  3. Integration ( Area under curve)

  4. Multiplicity of signals (signals)

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33

Number of signals

Chem equivalent protons resonate @ same frequency

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34

Chemical shift

Resonance frequency relative to TMS standard

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35

Integration

H ration

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36

Multiplicity of signals

Signal splits into n+1

n= # adjacent EQUIVALENT H

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37

Enthalpy (H)

pos(+) =endothermic

Neg(-) =exothermic

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38

Entropy (S)

Measure of disorder & # of states can occupy

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39

Ring structure ENTROPY(S) is ____ because of ______

Entropy=less DUE TO LIMIT ROTATION

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40

Exergonic G sign

neg(-) G

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41

Endergonic G sign

Pos(+) G

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42

Rxn type w/ K>1

Exergonic (-G)

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43

Rxn type K<1

Endergonic (+G)

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44

Exergonic energy chart

Reactants HIGHER than products

K>1

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45

Endergonic energy chart

Reactants LOWER than products

K<1

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46

Ea activation energy

Distance btwn reactants & peak

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47

Transition state

Peaks on graph

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48

E2 Zaitsev

E2 w/ Small bases = major confirmation

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49

E2 Hofmann

E2 w/ Large base= Minor

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50

E2 large bases example

tBu-

(ÂŁt)3CO-

LDA

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