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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

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slide1

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
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

  • more, less b. less, more c. same

______ bond ______ bond

______ reactive ______ reactive

slide3

s bonds p bonds

  • s bonds formed from end to end p bonds formed from side interaction to side interaction
  • ______ orbital overlap ______ orbital overlap
  • more, less b. less, more c. same
  • stronger__ bond 80 – 90 kcal/mole weaker_ bond 66 kcal/mole
  • less__ reactivemore__ reactive
characteristics of s and p bonds1
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 required

occurs at room temp. for rotation?

  Will free rotation occur at room temperature?

a. no b. yes c. can’t predict

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

a. C-C bond of ethane b. C=C of ethylene

c. CC of acetylene d. no difference

acid base reactions
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?

  • alkene = Lewis acid, H-X Lewis base
  • alkene = Lewis base, H-X = Lewis acid
overall reaction favorable or not
Overall Reaction: Favorable or Not
  • In this reaction, 1 s bond and 1 p bond is being replaced with 2 s bonds.
overall reaction favorable or not1
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?

  • 1 s bond and 1 p bond and the reaction would be favorable
  • 1 s bond and 1 p bond and the reaction would be unfavorable
  • 2 s bonds and the reaction would be favorable
  • 2 s bonds and the reaction would be unfavorable
slide11
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

electron density is easily donated why
Electron density is easily donated. Why?

a. p bond weaker than s bond

b. p electrons more accessible

c. Both a and b

d. Electrons on atom with high electronegativity

slide14
Enter the #’s of the reagents in the proper sequence that will synthesize 1-methylcylcohexanol from 1-methylcyclohexene
slide15
Enter the #’s of the reagents in the proper sequence that will synthesize 1-methylcylcohexanol from (bromomethyl)cyclohexane
slide16

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

citric acid cycle
Citric Acid Cycle
  • aconitase : enzyme (m.w.  89000)
hydration of cis aconitate to isocitrate after 180 flip
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. No c. Can’t be distinguished

an example of a biological electrophilic addition
An Example of a Biological Electrophilic Addition
  • Biosynthesis of a-Terpineol (found in pine oil)
hydroboration
Hydroboration
  • Which way would the B-H bond prefer to add if steric hindrance wasn’t a factor?
what would be the structure of the polymer formed from cationic polymerization of 2 methylpropene
What would be the structure of the polymer formed from cationic polymerization of 2-methylpropene?
slide26
Which of the following is a step in the mechanism for the following reaction if it is acid catalyzed?
which of the following is a major product of the following reaction used in carbohydrate synthesis
Which of the following is a major product of the following reaction used in carbohydrate synthesis?
slide29

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

slide30
Bottle contains bromine in water
  • Left test tube contains cyclohexane
  • Right test tube contains cyclohexene
a chemical reaction occurred
A Chemical Reaction Occurred
  • Which compound reacted?
  • 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 h 2 o is a complicating factor covered later
What might be a product of the reaction?(H2O is a complicating factor covered later)
mechanism of x 2 addition to alkenes
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 x 2 addition to alkenes1
Mechanism of X2 Addition to Alkenes
  • What reaction does the second step look like?

a. E2

b. Addition of HX

c. SN2

d. SN1

  • E1

(reaction of bromide anion with cyclic halonium ion)

mechanism of x 2 addition to alkenes2
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.

catalytic hydrogenation of alkenes
Catalytic Hydrogenation of Alkenes

Does this appear to be a syn or anti addition?

a. syn b. anti c. neither

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

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

oxidation of alkenes to diols
Oxidation of Alkenes to Diols
  • How could the trans diol be synthesized from cyclohexene?
slide46

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