Reactive Intermediates Flashcards

1
Q

Carbocation

A

Is a positive ion in which a positive charge resides on the carbon atom

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2
Q

Carbocation stability

A

Tertiary are most stable,

Pi systems adjacent to carbocation also stabilize via resonance

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3
Q

Carbocation rearrangement

A

Often occurs during Sn1 & E1 reactions

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4
Q

1,2 shift/ Wagner-Meerwein transposition

A

When a carbocation rearranges into a more stable tertiary carbocation

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5
Q

Carbanion

A

An ion in which a carbon atom has a -1 charge, often formed by heterolytic cleavage between carbon & a metal

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6
Q

Carbanion

A

Conjugate bases of hydrocarbons

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7
Q

Free radical

A

A neutral species that contains an impaired electron

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8
Q

Homolytic bond cleavage

A

He really form radicals, each fragment carries one electron from the broken bond

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9
Q

Alkyl radical

A

Primary, secondary, tertiary; methyl radical = methyl cation

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10
Q

Stability of free radical is associated with?

A

Their bond dissociation energies (BDE); the lower the BDE, the more stable the radical

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11
Q

Prototypical free radical reaction for chlorination of methane

A
  1. ) initiation
  2. ) chain propagation
  3. ) termination of propagation cycle
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12
Q

Initiation

A

The dissociation of he radical precursor molecule and the formation of two free radicals under light or high temperature

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13
Q

Chain propagation

A

The free radical abstract a hydrogen atom from the already; the the alkyl radical reacts with another precursor molecule

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14
Q

Termination of the propagation cycle

A

Occurs when free radicals combine with one another

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15
Q

Allylic

A

Carbon next to a C=C double bond; experiences enhanced free-radical reactivity

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16
Q

Benzylic

A

Carbon next to a benzene ring; enhanced free radical reactivity

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17
Q

Free radicals and carbocations are?

A

Both planar and sp2 hybridized

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18
Q

Carbenes

A

Are neutral molecules of general formula R2C: in which a carbon atom has two sigma bonds and two electrons

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19
Q

Benzynes

A

Compounds that are formed as reactive intermediates in the reaction of alkyl halides with strong bases (nuc aro sub)

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20
Q

Enols

A

Compounds that exist as an equilibrium mixture of ketone and alcohol tautomers. Two forms are called the Keto form and Emil form

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21
Q

Keto form vs enol form

A

Is more stable and predominates in simple ketones and aldehydes

22
Q

Organometallic compound

A

Consists of a carbon atom covalently bonded to a metal, carbon has a partial negative charge while meta has a partial positive charge

23
Q

Grignard reagents

A

Organomagnesium halides

24
Q

Preparation of Grignard reagent

A

Reaction between magnesium and alkyl halide (RX) in an ether solvent

25
Most common grignard solvent
Diethylether; donates unshared electrons to the empty orbitals in magnesium, while ethyl groups solvated the alkyl fragments
26
Grignard reagent most important reaction
Rxn with carbonyl compounds = forms tertiary alcohols
27
Formaldehyde + RMgX
Primary alcohol (RCH2OH)
28
Aldehyde (RCOH) + R'MgX
Secondary alcohol (RCHOHR')
29
Ketones (RCOR') + R"MgX
Tertiary alcohol (RCOHR'R")
30
CO2 + RMgX
Carboxlyic acid (RCOOH)
31
Organolithium reagents
More reactive than grignard reagents because Li is more electropositive than Mg
32
Organolithium reagent preparation
Prepared by rxn with an alkyl halide (TX) and Group 1 metal an parotid solvent
33
Organolithium reagent prep rxn
RX + 2M (Group 1) -> RM + M+X-
34
Lithium Organocuprates
Useful in coupling 2 alkyl fragments to produce larger alkane
35
Corey-House reaction
Rxn that uses lithium organocuprates to couple 2 alkyl fragments together
36
Lithium dialkylcuprates (R2-Cu-Li)
Preferred organometallic reagent for Corey-House reaction
37
Most commonly used lithium diaklylcuprates
Lithium dimethylcuprate (CH3)2 Cu-Li Lithium divinylcuprate (H2C=CH)2 Cu-Li
38
Dialkylcuprate prep
2RLi + CuX -> R2CuLi + LiX
39
Organozinc reagents prep rxn
RX + Zn -ether-> RZnX
40
Organozinc reagents reactivity
Not as reactive toward carbonyl compounds as RLi or RMg;
41
Organozinc prep
often formed at rxn intermediates in reduction Rina b/w alkyl halides and zinc in acid media
42
Simmons-Smith reaction
1. ) ICH2I + Zn -(ether/Cu)-> ICH2ZnI | 2. ) formation of cylcopropane by reaction with alkene
43
Oxymercuration rxn
Formed when Hg(O2CCH3)2 reacts with Alkenes in a mixture of H2O and THF
44
Oxymercuration
Forms: beta-hydrocyalkylmercury(II) acetate
45
Demercuration
Rxn that isolates oxymercuration product by treating it with sodium borohydride (NaBH4); yields an alcohol
46
Solvomercuration-demercuration reaction
Like oxymercuration but used to synthesize ethers by subbing an alcohol for THF
47
Benzenetricarbonyl chromium
Has three signs bonds b/w the CO groups and act and a benzene ring(not a phenyl group) attached to the metal act bonded to pi system
48
Cyclobitadiene tricarbonyliron
Pi complex
49
Ferrocene
Pi complex
50
Pi complexes
System where a metal is bonded to the pi system of s benzene ring