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A CH20150 > Nucleophilic Carbon species > Flashcards

Nucleophilic Carbon species Flashcards

1
Q

What is a real life equivalent for a cation alpha to a ketone

A
  1. Alpha-halo ketone

2. Undergo nucleophilic displacement fastly

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2
Q

How do you form a grignard reagent

A
  1. Formed from the corresponding alkyl or aryl halides and magnesium metal
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3
Q

What do grignard reagents act as and which part gives it the properties

A
  1. Act as carbon nucleophiles and react with many different electrophiles
  2. Mg is so electropositive out of Mg and C, carbon is more electronegative is acts as a nucleophile
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4
Q

What happens when a grignard reagent reacts with an aldehyde

A
  1. Gives secondary alcohol
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5
Q

What happens when a grignard reagent reacts with a ketone

A
  1. Gives tertiary alcohol
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6
Q

Why are Grignard reagents used more commonly than corresponding alkyllithiums

A
  1. Alkyllithium are very basic, which often leads to side reaction
  2. They are mainly just used as strong, irreversible bases
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7
Q

What are the synthons and then the real life equivalents for a secondary alcohol

A
  1. Synthons- primary alcohol cation and R-

2. RLE- Aldehyde and R-Mg-X

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8
Q

What are the synthons and then the real life equivalents for a tertiary alcohol

A
  1. Synthons- secondary alcohol cation + R-

2. RLE- ketone and R-Mg-X

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9
Q

What is the ideal angle for a carbon atom

A
  1. 109 degrees
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10
Q

What is the the angle in an epoxide and consequence

A
  1. 180

2. A lot of strain energy- wants relief of strain

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11
Q

What does reaction of epoxide and Grignard give and at what carbon does the Grignard react

A
  1. Alcohol

2. Reaction at least hindered position

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12
Q

What is the RLE of an alcohol where the +ve is not adjacent to the carbonyl

A
  1. Epoxide and grignard
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13
Q

What is a problem with using a grignard to alkylate an alpha-halo ketone

A
  1. It is an ambident electrophile- the nucleophile can react with it in more than one place
  2. Attack at carbonyl carbon or at alpha carbon (attached to halogen)- what is wanted
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14
Q

What type of nucleophilic carbon species is a grignard reagent

A
  1. A hard nucleophilic carbon species so reacts with harder electrophilic site
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15
Q

Which carbon site is harder in an alpha-haloketone

A
  1. The carbonyl carbon is the harder electrophilic site

2. The allyl halide is softer so requires a softer nucleophile

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16
Q

Generally what do hard nucleophiles have

A
  1. Hard nucleophiles have their lone pair and charge very localized and are not polarizable.
  2. Small with high charge density
17
Q

Generally what do soft nucleophiles have

A
  1. Soft nucleophiles have their lone pair either quite delocalized, or in a large orbital.
  2. Often elements further down the periodic table- react with more diffuse outer shell electrons
18
Q

Give an example of a soft nucleophilic carbon species

A
  1. Cuprate
19
Q

How do you form a cuprate

A
  1. Take an organometallic reagent that has been pre-formed (Grignard or an organolithium) and carry out a transmetallation
  2. E.g. Add CuCl to R-MgX
  3. Or add Cu SALT to 2 Eq of R-Li
20
Q

What copper salts can be used for transmetallation

A
  1. Cl, Br, I, CN
21
Q

How do you write a cuprate derived from a Grignard

A
  1. R-Cu

2. The precise structure is ill-defined it is actually loads of complex clusters

22
Q

How is the cuprate structure from an organolithium defined

A
  1. R-Cu(-)-R Li+
23
Q

When would a cuprate react directly with a carbonyl carbon

A
  1. Cuprates don’t generally react with carbonyls directly as they are too hard an electrophile
  2. But will react with acid chloride once, displacing the chloride
24
Q

How can acid chlorides be made

A
  1. Reacting the corresponding carboxylic acid with thionyl chloride or with oxalyl chloride/DMF
25
Q

What would happen if you added an Grignard to an acid chloride

A
  1. Grignard adds twice

2. End up with alcohol not ketone

26
Q

Cuprate + acid chloride–>

Grignard + acid chloride –>

A
  1. Ketone

2. Alcohol

27
Q

What happens if you only add one equivalent of Grignard to an acid chloride

A
  1. Ketone is more reactive than acid chloride

2. So still produce alcohol not ketone

28
Q

What else can cuprates be used for

A
  1. Very good at conjugate addition to alpha,beta-unsaturated carbonyl systems
  2. 1,4-addition
29
Q

Where would Grignard reagents effect in an alpha,beta-unsaturated carbonyl system

A
  1. 1,2-addition- at hard carbonyl electrophilic site
30
Q

What else can undergo conjugate addition to enones

A
  1. Heteroatom nucleophiles

2. Used for C-X bond formation

31
Q

What is a RLE for a carbonyl with +ve on beta carbon

A
  1. alpha-beta unsaturated carbonyl
32
Q

What can cuprates be used to open

A
  1. Open epoxides like Grignards

2. Cuprates can open aziridines (nitrogen containing equivalent of epoxides)

33
Q

What forms when a cuprate reacts with an aziridine

A
  1. Gives an amine

2. Reacts at least hindered position

34
Q

When the ring opening of an aziridine not work well and why

A
  1. When the R group attached to the N is an H
  2. All organometallics are basic- NH is easily deprotonated so if its NH, the organometal will act as base instead of nucleophile

A CH20150 (15 decks)

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