Lec 4

Question 1

Out of an aldehyde and ketone which one has the lower pKa (and therefore more likely to donate a H+)? Include a diagram in your answer

Answer 1

Aldehyde has lower pKa - B- (base) attacks an acidic H , eventually a -ve charge placed on carbonyl O Ketone has a higher pKa because methyl group constantly pushing electrons towards C making it slightly -ve therefore harder to put -ve charge on the O

Question 2

Out of an ester and a thioester which one has the lower pKa (and therefore more likely to donate a H+)?

Include a diagram in your answer

Answer 2

• thioester has lower pKa - competition from the O in the ester to push its lone pair into the C of the carbonyl reduces the ability of the removal of the acidic H - in the thioester (bigger p orbital of S) there is less orbital overlap and H is removed easier

Question 3

Thiol ester enolate anions play a key role in the biosynthesis of ___ ____ and _____ eg erthromyocin

Answer 3

fatty acids antibiotics

Question 4

Give the rules of assigning C oxidation states in.. C-C bond C-H bond C-(a more electronegative atom)

Answer 4

C-C bond = 0 C-H bond = -1 C-(a more electronegative atom) = +1

Question 5

For an inversion of configuration nucleophilic substitution @ which side does the Nu need to attack in relation to the leaving group?

Answer 5

Opposite side to the leaving group

Question 6

Draw the mechanism for removing an acidic H from a thiol ester enolate anion

Answer 6

Question 7

Give an example of an oxidation-reduction reaction

Answer 7

lactate dehydrogenase

lactate into pyruvate

lactate + NAD+ -> pyruvate + NADH + h+

Question 8

Draw the mechanism for an SN2 reaction using this starting product

Answer 8