L2 - P Block chem

Question 1

What is the role of POCl3?

Answer 1

Involved in the SN2 reaction of carboxylic acids to acid chlorides

Question 2

What is the pKaH of -OH?

Answer 2

16

Question 3

What is the pKaH of Cl-?

Answer 3

-7

Question 4

What is the role of the P atom in the formation of acyl chlorides?

Answer 4

It activates OH into a good leaving group

Question 5

What is the appel reaction?

Answer 5

formation of RCl from ROH

Question 6

What is the role of P in the appel reaction?

Answer 6

Nucleophile
Activates OH as a good leaving good
Forms PP3PO

Question 7

What reagents are required for the Appel reaction and what must take place before the reaction can occur?

Answer 7

PPh3
CCl4
They react together to form PPh3Cl+ which reacts

Question 8

What is the purpose of the appel mechanism?

Answer 8

Ch2Cl bonds to undergo other reactions

Question 9

What is the wittig reaction?

Answer 9

Addition of a phosphorus ylide to a carbonyl to form a C=C bond.

Question 10

What is a phosphorus ylide?

Answer 10

Species which carries both a positive and a negative charge on adjacent atoms

Question 11

What is the driving force for the Wittig reaction?

Answer 11

Thermodynamics

There is 83kJmol-1 of energy gained when the new bonds are formed

Question 12

What is the total bond energies of the reactants and products of the wittig reaction?

Answer 12

Reactants = 1064 kJmol-1
Products = 1146 kJmol-1

Question 13

What type of reactions is the wittig reaction thought to go by?

Answer 13

Concerted
thermal [2+2] cycloaddition
2nd step is [2+2] reaction

Question 14

What nature R group will give a E product in the Wittig reaction?

Answer 14

R groups which stabilise the negative charge

Stabilised ylides

Question 15

What nature R groups will give a Z product in the Wittig reaction?

Answer 15

R does not stabilise the negative charge

Unstabilised ylides

Question 16

What does the selectivity of the Wittig reaction rely on?

Answer 16

The nature of the R group on ylide