• The following three slides leads students to realize that free rotation around C=C bonds does not occur at room temperature.

Characteristics of s and p Bonds s bonds p bonds s bonds formed from end to end p bonds formed from side

interaction to side interaction

 ______ orbital overlap ______ orbital overlap

a. more, less b. less, more c. same

______ bond ______ bond______ reactive ______ reactive 

s bonds p bonds s bonds formed from end to end p bonds formed from

side interaction to side interaction

______ orbital overlap ______ orbital overlap

a. more, less b. less, more c. same

stronger__ bond 80 – 90 kcal/mole weaker_ bond 66 kcal/moleless__ reactive more__ reactive

Characteristics of s and p Bonds

cylindrically symmetrical not cylindrically symmetrical  

~ > 3-5 kcal/mole p orbitals must be in same required for rotation plane for bond. What

happens to the bond if the orbitals don't overlap?

 a. Nothing b. bond becomes stronger c. bond breaks   

“Free" rotation How much energy is requiredoccurs at room temp. for rotation?

  Will free rotation occur at room temperature?

a. no b. yes c. can’t predict

66

Alkynes

• Which has the greatest overall bond strength in the 3 structures?

a. C-C bond of ethaneb. C=C of ethylene

c. CC of acetylene d. no difference

H3C CH3 H2C CH2 HC CH

1.54 A 1.33 A 1.20 A

Which compound will form preferentially? A or B

OHH3PO4

+

A B

Acid-Base Reactions

When an alkene reacts wit H-X, this is also a Lewis Acid-Base reaction.

 

Which is the Lewis acid and which is the Lewis base?

 

a. alkene = Lewis acid, H-X Lewis base

b. alkene = Lewis base, H-X = Lewis acid

• The next two slides explains the exothermicity of additions across p bonds.

Overall Reaction: Favorable or Not

• In this reaction, 1 s bond and 1 p bond is being replaced with 2 s bonds.

C C

R R

R R

+ H X C

H

R

R

C

X

R

R

Overall Reaction: Favorable or Not

What would you expect to be stronger 1 s bond and 1 p bond or 2 s bonds? Would you expect the reaction to be favorable or unfavorable then?

 

a. 1 s bond and 1 p bond and the reaction would be favorable

b. 1 s bond and 1 p bond and the reaction would be unfavorable

c. 2 s bonds and the reaction would be favorable

d. 2 s bonds and the reaction would be unfavorable

• Forward Reaction : elimination of H-Br from bromoalkane to give alkene

• Reverse Reaction : What is happening in the reverse reaction?

a. SN2 reaction

b. SN1 reaction

c. E1 reaction

d. E2 reaction

e. Addition reaction

CH3C

CH3

CH3

Br H3C C

CH3

CH

H

H

+ BrH3C

C

CH3

CH2

+ H+

or HBr

Electron density is easily donated. Why?

a. p bond weaker than s bondb. p electrons more accessiblec. Both a and bd. Electrons on atom with high

electronegativity

CC

Which of the following could initiate the cationic polymerization of styrene?

Ph ? H2C C

Ph

H nstyrene

C

Ph

Ph Ph

SbCl5-

B

F

F F

F

Al

Cl

Cl Cl

Cl

H-Br

a. b. c. d. e

Enter the #’s of the reagents in the proper sequence that will synthesize 1-methylcylcohexanol from 1-methylcyclohexene

SOCl2 N1 D2O 2 Raney Ni, EtOH 3 Mg, Et2O(Li, THF)

4 Cl2 5

6 H2O 7 -OD 8 HCl 9 NaNH2, NH3 10 CH3CH2O-, CH3CH2OH,

11 H2SO4, H2O 12 Na 13 CH3CH2Br 14 PBr3

OHH2SO4,H2O

11

Enter the #’s of the reagents in the proper sequence that will synthesize 1-methylcylcohexanol from (bromomethyl)cyclohexane

SOCl2 N1 D2O 2 Raney Ni, EtOH 3 Mg, Et2O(Li, THF)

4 Cl2 5

6 H2O 7 -OD 8 HCl 9 NaNH2, NH3 10 CH3CH2O-, CH3CH2OH,

11 H2SO4, H2O 12 Na 13 CH3CH2Br 14 PBr3

OHH2SO4,H2O

Br

CH3CH2O-

CH3CH2OH,

10,11

• The next 3 slides compares the mechanism in a biological hydration to the recently covered acid catalyzed hydration.

Citric Acid Cycle

• aconitase : enzyme (m.w. 89000)

OHO

OOO

O

O

O

OOO

O

O

O

OOO

O

O

OH

aconitase aconitase

elimination hydration

Hydration of cis-Aconitate to Isocitrate

H

C

-O2C

C

CO2-

-O2C

H

O

H

His 101

101 His H

OH

CH

CO2-

C

-O2C

CO2-

OH

CH

CO2-

C

-O2C

CO2-

H O Ser 642OH

CH

CO2-

C

-O2C

CO2-

HO Ser642

Hydration of cis-Aconitate to Isocitrate After 180 Flip

Is this the same mechanism as that shown for the addition of water to 2-methypropene using sulfuric acid as a catalyst?

 

a. Yes b. Noc. Can’t be distinguished

• The next 2 slides are part of one question.

An Example of a Biological Electrophilic Addition

• Biosynthesis of a-Terpineol (found in pine oil) PPO

OH

PHO

O

OH

O P

O

O

OH

P

O

OH

O = -OPP a good L

Which of the following in not a step in the mechanism of the reaction?

OHO H

H

a.

H2O

O H

H

b.

c.

H2O

O H

H

d.

PPO

e.

Hydroboration

• Which way would the B-H bond prefer to add if steric hindrance wasn’t a factor?

H

B

B

H

H

B

B

H

+

A B C

H

B

A

Which structures appears to have less electron repulsion between the atoms?

HB

H

H

BH

H

H

A B

What would be the structure of the polymer formed from cationic polymerization of 2-methylpropene?

a. b. c.

d. e.

CH2 C

CH3

CH3 n

CH C

CH3

n

CH2 C

CH3

H n

CH2

H2C

n

C

CH3

CH3 n

Which of the following is a step in the mechanism

for the following reaction if it is acid catalyzed?

a. b. c.

d. e.

+ H2O

OH

+ H+

O

+ H2O

H H

+ -OH

OH

+ -OH

OH

Which of the following is a major product of the following reaction used in carbohydrate synthesis?

a. b. c.

d. e.

O

OH

HOHO

H2SO4+ CH3OH

O

OHHO

HOOH

O

OHHO

HO

HO

O

OHHO

HO

HO

OH

O

OHHO

HO

H3CO

O

OHHO

HOOCH3

Predict the major stable product of the following reaction.

1. B2H6

2. NaOH, H2O2

OH

HO

BH2 OH OH

A B C D E

• The next 5 slides asks students to explain experimental results after they have already learned something about electrophilic addition.

• Bottle contains bromine in water• Left test tube contains cyclohexane• Right test tube contains cyclohexene

Bromine/H2O is added to each test tube

After Shaking

A Chemical Reaction Occurred

• Which compound reacted?

a. Cyclohexane b. Cyclohexene

• What type of bond most likely was involved in the reaction?

a. C-H s bond b. C-C s bond c. p bond

What might be a product of the reaction?(H2O is a complicating factor covered later)

Br Br

Br

Br

Br

Br

a b c d

Mechanism of X2

Addition to Alkenes

• In the first step, what is the reactive intermediate formed called?

a. cyclic halide ion

b. cyclic halidium ion

c. cyclic carbocation

d. cyclic halonium ion

e. cyclic halocarbocation

Mechanism of X2

Addition to Alkenes

• What reaction does the second step look like?

a. E2

b. Addition of HX 

c. SN2

d. SN1

e. E1

(reaction of bromide anion with cyclic halonium ion)

Mechanism of X2

Addition to Alkenes

• Why does only the trans product form?

a. The reactive intermediate is resonance stabilized.

b. The reactive intermediate is stabilized by the alkyl groups.

c. SN2 reactions require backside displacement.

d. The trans product is more stable.

e. The bromide ion is too unreactive.

Br2, CH3OH

CH3

OHBr

H

CH3

OCH3Br

H

OCH3

CH3Br

H

OH

CH3Br

H

Br

CH3H

Br

a. b. c. d. e.

Predict the major product of the following reaction.

Catalytic Hydrogenation of Alkenes

Does this appear to be a syn or anti addition? a. syn b. anti c. neither

CH3

CH3

H

HCH3

CH3

H2, "Pt",

high pressure

Carbenes

• Based on this structure, would you expect a carbene to be an electrophile or nucleophile?

a. nucleophile b. electrophile c. neither d. both

R

C

R

- only 2 bonds

- 6 valence e -

C

R

R

p

"sp2 hybridized C"

"sp2 hybrid orbital"

(

O

H H

O

+

1. O3

2. Zn, H2Oalkene ?

a. b.

c. d.

Oxidation of Alkenes to Diols

• How could the trans diol be synthesized from cyclohexene?

OH

OH

1. MCPBA 2. (1. OsO4 2. Na2SO3, H2O) 3. PtO2

4. KMnO4, H2O, OH- 5. Cl2, H2O 6. excess NaOH, H2O

7. H2SO4, H2O 8. BH3 9. H2O2, NaOH

16 or 56

Predict the major stable product(s) of the following reaction.

H3C

C C

CH2CH3

H

H

Br2, CCl4

Br

C C

Br

H3C CH2CH3

HH

Br

C C

Br

H HCH2CH3H3C

Br

C C

Br

H CH2CH3

HH3C

Br

C C

Br

H3C HCH2CH3H

Br

C C

CCl3

H3C CH2CH3

HH

Br

C C

CCl3

H HCH2CH3H3C

Cl3C

C C

Br

H CH2CH3

HH3C

Br

C C

CCl3

H3C HCH2CH3H

Br

C C

Br

H3C CH3

HH

++

a. b.

c.

+ +

d.

e.

Predict the major stable product(s) of the following reaction.

O O O

C C

HO OH

H H

C C

HO OH

HH

C C

HO OH

HH

C C

O3Os OH

HH

C C

HO OsO3

HH

a. b.

c. d.

e.

1. OsO4

2. Na2SO3, H2O

How could the oxirane be synthesized from but-2-yne?

H3C C C CH3

O?

1. MCPBA 2. (1. OsO4 2. Na2SO3, H2O) 3. H2, PtO2

4. H2, Pd/CaCO3, PbO 5. CH2O h 6. (1. BH3 2. H2O2, NaOH )

7. H2SO4, H2O 8. (1. Hg(OAc)2, H2SO4, H2O 2. NaBH4, NaOH )

9. (1. Na, NH3 2. NH4OH)

41

• In the biosynthesis of fatty acids, the crotonyl ACP is converted to butyryl ACP. What type of reaction does it formally appear to be?

a. dehydration b. hydration

c. alkyl shift d. hydrogenation

e. hydride shift

H3C CH

CH

C

O

SACP H3CH2C

H2C C

O

SACP

NADPHmultienzymecomplex