Midterm 2 Must Have Memorized

Question 1

pKa of hydronium ion and protonated alcohol?

Answer 1

-2

Question 2

pKa of carboxylic acid?

Answer 2

5

Question 3

pKa of alcohol and water?

Answer 3

16

Question 4

pKa of phenol?

Answer 4

9

Question 5

pKa of protonated carbonyl group?

Answer 5

-4

Question 6

pKa of ketone?

Answer 6

20

Question 7

pKa of ester?

Answer 7

25

Question 8

pKa of ammonium ion?

Answer 8

9

Question 9

pKa of protonated amine?

Answer 9

11

Question 10

pKa of thiol?

Answer 10

11

Question 11

pKa of diisopropylene?

Answer 11

37

Question 12

pKa of amine?

Answer 12

33

Question 13

pKa of amide?

Answer 13

15

Question 14

pKa of alkane?

Answer 14

60

Question 15

pKa of mineral acids?

Answer 15

around -5 to -10ish

Question 16

What are the 5 requirements for SN2 reactions?

Answer 16

1. Nucleophile must be a conjugate base of a weak Bronsted acid with approximately pKa = 4.5
2. C-X bond must be polarized: partial positive charge on C and partial negative charge on X
3. The structure of C-X permits facile access to the C-lobe of the anti-bonding C-X orbital
4. X- (leaving group) is the conjugate base of a Strong Bronsted acid with pKa < 0
5. Nucleophile must be a stronger Bronsted base than X-

Question 17

What is the primary driving force for SN2 reactions?

Answer 17

Decrease in basicity of the medium (delta pKa must be very negative so delta G is very negative and the reaction is favourable)

Question 18

What are the relative rates for SN2 reactions with methyl, primary, secondary halides?

Answer 18

SN2 reaction will be the fastest with methyl and slowest with secondary halides because of steric hinderance of the C-X anti bonding orbital.

Question 19

Can tertiary alkyl halides undergo SN2 reactions?

Answer 19

NO, too much steric hinderance.

Question 20

What are two structures that assist in biosynthesis and when are they used?

Answer 20

1. H-A-Enz is used to in an electrophilic addition to alkenes type of reaction to remove a double bond and create a positive charge and produce a carbocation so a nucleophilic attack and cyclization can occur.
2. Enz-B: has electrons so E1 reaction can occur and an alkene can be produced.

Question 21

A linear molecule with a hydroxyl group on the other end of a carbonyl group will form what?

Answer 21

A CYCLIC STRUCTURE. Could be an ester if you are adding an alcohol, H-A, and carboxylic acid together.

Question 22

In a aldopentose pyranose, what carbon do you decide R/S and D/L configuration?

Answer 22

At the carbon next to the CH2

Question 23

What reaction requires heat?

Answer 23

Hydrolysis of amides

Question 24

How do we form alkoxides (O-)

Answer 24

NaH. H- will deprotonate anything with pka up to 30.

Question 25

What is basicity? Why does lowering basicity in a chemical reaction a driving force?

Answer 25

Basicity: electron-pair instability.

By lowering basicity, you increase stability, lower energy, favourable.