Chapter 2 Chemistry Answers

Introduction to Bioorganic Chemistry and Chemical Biology: ANSWERS TO CHAPTER 2

Answer 2.9 [HA] Henderson–Hasselbalch:

log [HA]

Rearranged:

= pK a – pH

[A–]

= 10(pK a – pH)

[A–]

A

10(9.2–7.2) = 100; [HCN]/[CN –] = 100:1

B

10(9.2–7.2) = 100; [NH 4+]/[NH3] = 100:1

C

10(4.2–7.2) = 0.001; [PhCO 2H]/[PhCO2–] = 1:1000

Answer 2.10 OH Ca +O H

HO

(HO) 2Ca

..

O

OH

O

HO - OH Ca

.   .  

R

:

B

O

.

. .

R

OH

OH -Ca + O O

R

OH

OH Ca +O O

R

OH

CaOH O

R

OH

.

..

O

R

OH OH Ca +O O

O

O

. .

OH

R

OH

R

OH

OH

Note that the actual equilibrium will involve all possible diastereomers. Answer 2.11 O

: A 

O: NH

H 3C

H3C

N H2+

H3C

NC:

+ OH2 NH2

H 3C

H

3

H3C

..

H

- O:

NH2

 A 

 A 

H

: OH

H3C

NH2

CN NH2+

H 3C

NH2

Answer 2.12 A

Use the following equation. E

4 q1 × q2 

ε

+

 x  r 12

r 

–

 y  r 6

Only the Coulombic, first term is relevant for the charge–charge repulsion. Substitute the distances given as r  into the Coulombic equation as follows. 4 q1 × q2 ε

3

4 q1 × q2 ε

= 2/3

2

In other words, the repulsive interaction potential decreases by about 33%. B

Here, only the third term for the attractive interaction is relevant, because the first two terms can be approximated as zero. We can compare the attractive energies at those two differences by taking the ratio.  y  36

= (2/3)6 = 0.088

 y  26

 Thus, the attractive interaction potential decreases by more than 90%.

3

6

Introduction to Bioorganic Chemistry and Chemical Biology: ANSWERS TO CHAPTER 2

*Answer 2.28    O    H

   OH

   O    H

   OH

 A  H

α-ribofuranose

..

   O   -

ribose H

OH

+

   O    H

H

OH

O

   O    H

   O    O    H

H

-A :

   OH OH

HO

   O +

   OH

   O    H

OH  A  H

..

..    O   -

HO

   O + H

+

   O    H

H

-A :

β-ribofuranose

   O    O    H

*Answer 2.30 A

23 = 8 stereoisomers

B

D-ribose

H

OH

L-ribose

OH

OH

OH

H

O

O OH

OH

OH

OH

*Answer 2.33 :

N C N H2

aminonitrile

N:

NH3 H2N

+N H

:B

H H

- N: H2N

N H

H

H NH3

+

NH H2N

NH2

guanidine