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Organic Chemistry > Organic Test 3 > Flashcards

Organic Test 3 Flashcards

1
Q

Acid- Catalyzed Dehydration of an Alcohol Mechanism

A

By the E1 mechanism

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2
Q

What two different reagants can be used if you want to form an anti-diol from an alkene?

A
  1. MCPBA then H3O+
  2. CH3CO3 in water
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3
Q

Mechanism for Ionic Addition of HX to an alkene

A
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4
Q

Stability of Cis/Trans isomers

A

Trans isomers are generally more stable than the corresponding cis isomers.

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5
Q
A
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6
Q

oxymercuration-demercuration mechanism

A

**Results in a Markovnikov addition of OH and H without rearrangement. Use if you don’t want it to rearrange!

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7
Q

Free-Radical Halogenation of HBr

Result with peroxide

A

Results in an anti-markovnikov addition in the presence of peroxide

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8
Q

Platinum and H2 as reagants together do what ____

A

reduce alkene to alkane

(hydrogenation)

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9
Q

What is the mechanism for an Acid-Catalyzed opening of an Epoxide?

A
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10
Q
A
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11
Q

Mechanism for Hydroboration of an alkene

A

**anti-mark

**syn-addition

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12
Q

Alkenes as Substituents

A

alkenyl groups:

methylene

vinyl

allyl

phenyl

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13
Q

What two reagants are used for oxidative cleavage of alkenes and what is the difference between them?

A
  1. KMnO4 (warm/conc.)

harsh, can’t recover aldehydes they are further oxidized into alcohols.

  1. O3

then (CH3)2S

can recover aldehydes

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14
Q

Addition of Hydrogen Halides to Alkenes

A
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15
Q

An E2 elimination takes place on a chair confirmation only if the proton and leaving group are _____

A

transdiaxial

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16
Q

E-Z nomenclature

A

If the two first-priority atoms are together (cis) on the same side of the double bond, you have the Z isomer, from the German word zusammen, “together.”

If the two first-priority atoms are on opposite (trans) sides of the double bond, you have the E isomer, from the German word entgegen, “opposite.”

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17
Q

Equation for Elements of Unsaturation

A

=(1/2)(2C+2-H)

C= Carbon

H= Hydrogen

Double bond= 1 element of unsaturation

A ring= 1 element of unsaturation

A triple bond= 2 elements of unsaturation

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18
Q

Zaitsev’s rule (stability of double bonds)

A

More substituted double bonds are usually more stable.

The alkyl groups attached to the double bonded carbons stabilize the alkene.

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19
Q

If an alkene can not easily undergo hydration in aqueous acid, what reagant can be used?

A
  1. Hg(OAc)2/ H2O
  2. NaBH4

(oxymercuration-demercuration)

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20
Q

Energy Differences in cis-trans isomers

A

Trans isomers are generally more stable than the corresponding cis isomers. In this case, the alkyl substituents are separated farther in trans isomers than they are in cis isomers.

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21
Q

Mechanism for the formation of Halohydrins (OH and X) from alkenes

A
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22
Q

What reagants are necessary to turn a double bond into a dibromocyclopropane?

A

CHBr3

KOH

and H2O

**cis/trans isomerism retained

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23
Q

Summary for naming Alkenes

A
  1. Select the longest chain or largest ring that contains the largest possible number ofdouble bonds, and name it with the -ene suffix.
  2. Number the chain from the end closest to the double bonds. Number a ring so that the double bond is between carbons 1 and 2. Place the numbers giving the locations of the double bonds in front of the root name (old system) or in front of the suffix -ene,
    - diene, etc. (new system).
  3. Name substituent groups as in alkanes. The ethenyl group and the propenyl group are usually called the vinyl group and the allyl group, respectively.
  4. Remember E-Z Nomenclature if you can’t use Cis/Trans. (Also, never forget R/ S if necessary)

(diene,triene,tetraene,etc)

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24
Q

What is a peroxide?

25
Q

What is the reagant necessary for catalytic hydrogenation (adding H2 across a double bond)?

What is the stereochemistry?

A

syn-addition

26
Q

What reagant can you use to form an acetylide ion?

27
Q

Dehydrohalogenation by the E2 mechanism

A

Reliable if poor SN2 substrate. One step.

28
Q

In aqueous conditions, what reagant can be used to create an epoxide?

A

peroxyacetic acid (CH3CO3H)

29
Q

When an epoxide is in a solution of ____ you end up with the anti-addition of 2 OH, a diol.

A

H3O+

epoxides are unstable in acid conditions

30
Q

Result of Branching on boiling point of Alkenes

A

increased branching lowers boiling point

32
Q

Bredt’s Rule

A

** If there is a double bond at the bridgehead carbon of a bridged bicyclic system, one of the two rings contains a cis double bond and the other must contain a trans double bond.

**If the larger ring contains at least eight carbon atoms, than it can contain a trans double bond, and the bridgehead double bond is stable

33
Q

What reactants allow you to debrominate vicinal dibromides

A

NaI/ Acetone

By the E2 mechanism

34
Q

Stereochemistry of HBr, HCl, and HI when added to an alkene

A

forms an alkane that follows Markovnikov’s Rule.

Cation forms more stable intermediate (tertiary)

35
Q

What is formed in the simmons-smith reaction (CH2I2/ Zn(Cu))

36
Q

Reactant used to dehydrate alcohols into alkenes

A

conc. H2S04/ Heat

or H3PO4

37
Q

Mechanism of Debromination of Vicinal Dibromides

38
Q

Mechanism for the Formation of Carbenes

39
Q

Formation of a Hofmann product

A

-due to steric hindrance

40
Q

Stereochemsitry of Halogen Addition

A

**anti-addition.

41
Q

Acid-Catalyzed Hydration of an Alkene

A

**Follows markovnikov’s Rule

42
Q

What do you use if you want to add H and OH across a double bond in an anti-markovnikov and syn fashion?

A
  1. BH3THF
  2. H2O2/ -OH
43
Q

Hydration of an Alkene

44
Q

Numbering IUPAC rules

A

The chain is numbered starting from the end closest to the double bond, and the double bond is given the lower number of its two double-bonded carbon atoms

45
Q

Stereochemistry of the E2 reaction

46
Q

Alkoxymercuration- demercuration

47
Q

Order of reactivity of alcohol dehydrogenations

A

Go through the E1 mechanism

tertiary>secondary>> primary

Rearrangements are COMMON

48
Q

Anti-mark addition of H and Br to reduce alkene to alkane needs:

A

HBr and R-O-O-R (peroxide)

(**Doesn’t happen with HCl and HI)

49
Q

What two different reagants can be used if you want to form a syn-diol from an alkene

A
  1. OsO4/ H2O2

**expensive/highly toxic/volatile

  1. KMnO4/H20 (cold/dilute)

**cheap/ low yield/safer

***both are syn because the two Oxygens add at same time

50
Q

By what mechanism can an acetylide ion create larger organic molecules?

A

By an SN2 mechanism

Need a strong base/ good nucleophile

Primary and unhindered

**If hindered, the acetylide ion may abstract a proton, giving an E2 mechanism.

52
Q

Mechanism for Free Radical Additon of HBr to Alkenes

53
Q

Addition of Halogens to Alkenes

54
Q

Treat an alkene with ____ to reduce to an alkane (hydrogenation)

A

platinum catalyst and H2

55
Q

Stability of Cycloalkenes

1) less than 5-membered
2) 5-membered or greater

A

1) less than 5-membered rings are unstable (ring strain)
2) 5-membered or greater rings are stable if cis. Trans rings must be 8-membered or larger to be stable.

56
Q

What reagant is used to turn an alkene into an epoxide? What is the configuration?

A

MCPBA

**retains stereochemistry

57
Q

Order of carbocation stability

58
Q

Markovnikov’s Rule

59
Q

What reagants are necessary to turn an alkene into a halohydrin (add an X and OH?)

A

X2 and H2O (aqueous)

**anti addition

**markovnikov

Organic Chemistry (8 decks)

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