nucleophilic addition onto aldehydes and ketones

Question 1

How can it be proven that carbonyls are the most reactive functional group?

Answer 1

it can be shown through

• dipole moment
• resonance structure = double bond adds an extra pair of electrons to the oxygen atom

Question 2

What are addition reactions? What is nucleophilic addition?

Answer 2

reaction which breaks double bonds when the reactant attacks and adds onto the structure
- nucleophilic addition is an addition reaction using a nucleophile

Question 3

What are Grignard reagents?

Answer 3

RMgX - Grignard reagent
R - alkyl group, Mg -magnesium, X - halogen
react with carbonyls = nucleophilic addition (break double bond)
- formaldehyde = makes a primary alcohol
- aldehydes = make a secondary alcohol
- ketones = make a tertiary alcohol
- esters = react twice with esters, first they form an aldehyde then with the second reaction they form an alcohol (tertiary)

Question 4

What are organometallic? How do organometallics react with carbonyls?

Answer 4

organometallic are R groups attached to a metal
R-Li or R-Mg

organometallics react with carbonyls to form alcohols

Question 5

What type of alcohol do Grignard reagents form with ketones, aldehydes and formaldehyde?

Answer 5

formaldehyde - primary alcohol
aldehydes - secondary alcohol
ketones - tertiary alcohol

Question 6

What are the polarities on a Grignard reagent?

Answer 6

Grignard reagent = RMgX

• a Grignard reagent switches the polarities of the C atom in the alkyl with the Mg
• the C atom has a negative charge
• Mg has a positive charge

allows the Grignard reagent to react with carbonyls and positive charge carbon atoms
- carbocations

Question 7

What are the requirements for a Grignard reagent to form?

Answer 7

Mg
ether
- to stabilise the Grignard reagent in solution = 2 molecules coordinate with the magnesium

Question 8

Why are ethers required in Grignard reagent formation?

Answer 8

ethers stabilise the reaction
- non-acidic (no acidic protons) = will not protonate the Grignard reagent which would result in the reaction ending

Grignard reagents react with solvents like water which are acidic and form alkanes

Question 9

Why must a Grignard reaction occur under anhydrous conditions?

Answer 9

anhydrous conditions - in the absence of water

• water reacts with the Grignard reagent and protonates it = water acts as an acid
• Grignard are powerful bases = deprotonate water
• forms a hydrocarbon

Question 10

What are the different reactive forms of hydrogen?

Answer 10

atom (radical)
- hydrogen atom is a radical
- has 1 proton and 1 electron = is neutral
- reactive species = due to unpaired electron
proton
- form as hydrogen radical loses an electron = oxidation
- 1 proton
- acid form
hydride
- forms as hydrogen radical gains an electron = reduction
- 1 proton and 2 electrons
- basic/nucleophilic form

Question 11

Why are there no free hydrides in sodium borohydride?

Answer 11

boron forms a bond with hydride

- breaking the bond releases the pair of electrons that reduce carbonyls