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CHY1101 - Organic chemistry > Reduction > Flashcards

Reduction Flashcards

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1
Q

What is reduction?

A

Gain of hydrogen

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2
Q

What is H-?

A

Always a base

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3
Q

Is H- hard or soft? Why?

A

Hard

High charge density

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4
Q

What are the two types of hydride?

A

From X-H bond

From NaH splitting

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5
Q

What are the common hydride reducing agents?

A

NaBH4

LiAlH4

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6
Q

Which hydride reducing agent is less reactive?

A

NaBH4

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7
Q

What is classed as dry?

A

50ppm water

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8
Q

How must LiAlH4 be used?

A

Dry

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9
Q

Why are esters, amides and carboxylic acids not as well attacked by nucleophiles?

A

They have their negative charge delocalised across the molecules

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10
Q

What determines the reactivity of a carbonyl molecule?

A

The size of delta plus

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11
Q

In NaBH4, what is the nucleophile?

A

The B-H bond

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12
Q

What is a hydride?

A

Hydrogen plus a pair of electrons

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13
Q

Which reduction is chemoselective?

A

NaBH4

Reduces some molecules, aldehydes/ketones, but not others, esters/amides

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14
Q

Why cant you kick out bromine from an alkane with a hydride but you can break a carbonyl?

A

There is only slight polarisation of C-Br

There is a larger positive charge on carbon on carbonyl due to the electronegative oxygen

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15
Q

How many hydrides are used in the reduction of esters?

A

2

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16
Q

How many hydrides are used to reduce an aldehyde/ketone?

A

1 hydride

17
Q

How many hydrides are used to reduce amides?

A

2 hydrides

18
Q

How many hydrides are used to reduce a carboxylic acid?

A

3

19
Q

Which reducing agent is good to use and why?

A

NaBH(tBuO)3

Very unlikely to have any hydrides left

20
Q

Why is it important to have no hydrides left?

A

They will react with water

21
Q

How does LiAlH4 react with water?

A

Reacts violently

Fires

22
Q

What is LiAlH4 usually used in?

A

Anhydrous ethers

Et2O, THF

23
Q

What are the steps to reduce an ester to an alcohol?

A

Ester to aldehyde

Aldehyde to alcohol

24
Q

In the reduction of amides, what leaving group is kicked out?

A

O-AlH3

25
Q

What gas is released in the reduction of acids?

A

H2

26
Q

What are the steps of the LiAlH4 reduction of acids?

A

Formation of lithium carboxylate; ROOLi
Reduction of C=O group
Loss of aluminium salt - formation of aldehyde
Reduction of aldehyde
Acid hydrolysis of Al-alkoxide gives alcohol

CHY1101 - Organic chemistry (22 decks)

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