Solved Practice Questions: R/S, Chiral or Achiral, Enantiomer or Diastereomer? | Organic Chemistry PDF Download

 Page 1


	 1	
Organic Chemistry I    Test 2  Extra Stereochemistry Practice Problems 
Page 1:  Designate R/S Page 2:  Chiral or Achiral?   Page 3:  Same, Enantiomer, or Diastereomer? 
 
A.  Designate the R/S configuration for any chiral centers in the following molecules. 
 
1.  
 
2.  3.  
4.  
5.  
 
6.  
7.  
 
8.  
9.  
10.  
 
 
11.  
12.  
13.  
 
 
14.  
15.  
16.  
 
 
17.  
18.  
19.  
 
 
20.  
21.  
22.  
 
 
23.  24.  
25.  
26.  
 
 
27.  
28.  
 29.  
30.    
  
Br H H Br H H
2
N
Br H
HO
H
OH
OH H
HO
OH H
HO
O
NH
2
H
OH
O H
OH
OH
Br H
HO
O O
CH
3
H
O O
CH
3
H
N
H
O
CH
3
H
NH
2
OH H
HO OH
OH H
O
OH H
O
H H
3
CO
CH
3
H
OH H
O
NH
2
H
CH
3
OH H
H
2
N
OH
H
CH
3
Br
CH
3
CH
3
H
H
HO
O
H
NH
2
H
H
NH
2
H
3
C
H
CH
3
CH
3
H
HO
CH
3
CH
3
H
H
CH
3
HO
H
CH
3
H
H
OH
O
H
H
Cl HO
O
H
3
C
H
O
CH
2
OH H
H
HO
HO
H
H HO
H
OH
This one is very hard.
But for each of the 5 chiral C's, the tie-
breaking processes do work.  
The upper-left S is harder than the others.
R,R
R,R, error in movie 
which said R, S.
Priorities:  1.  Heteroatom.         2.  C-with-heteroatom. 
3.  C > CH > CH2 > CH3. 
4.  Proceed down chain until point of difference. 
Really
Hard!
Page 2


	 1	
Organic Chemistry I    Test 2  Extra Stereochemistry Practice Problems 
Page 1:  Designate R/S Page 2:  Chiral or Achiral?   Page 3:  Same, Enantiomer, or Diastereomer? 
 
A.  Designate the R/S configuration for any chiral centers in the following molecules. 
 
1.  
 
2.  3.  
4.  
5.  
 
6.  
7.  
 
8.  
9.  
10.  
 
 
11.  
12.  
13.  
 
 
14.  
15.  
16.  
 
 
17.  
18.  
19.  
 
 
20.  
21.  
22.  
 
 
23.  24.  
25.  
26.  
 
 
27.  
28.  
 29.  
30.    
  
Br H H Br H H
2
N
Br H
HO
H
OH
OH H
HO
OH H
HO
O
NH
2
H
OH
O H
OH
OH
Br H
HO
O O
CH
3
H
O O
CH
3
H
N
H
O
CH
3
H
NH
2
OH H
HO OH
OH H
O
OH H
O
H H
3
CO
CH
3
H
OH H
O
NH
2
H
CH
3
OH H
H
2
N
OH
H
CH
3
Br
CH
3
CH
3
H
H
HO
O
H
NH
2
H
H
NH
2
H
3
C
H
CH
3
CH
3
H
HO
CH
3
CH
3
H
H
CH
3
HO
H
CH
3
H
H
OH
O
H
H
Cl HO
O
H
3
C
H
O
CH
2
OH H
H
HO
HO
H
H HO
H
OH
This one is very hard.
But for each of the 5 chiral C's, the tie-
breaking processes do work.  
The upper-left S is harder than the others.
R,R
R,R, error in movie 
which said R, S.
Priorities:  1.  Heteroatom.         2.  C-with-heteroatom. 
3.  C > CH > CH2 > CH3. 
4.  Proceed down chain until point of difference. 
Really
Hard!
	 2	
 
B.  Identify each of the following molecule as chiral or achiral.  (By circling the chiral ones.)  
Write “meso” where it applies.  (In other words, if it is achiral despite having chiral centers).   
 
31.  
 
 
 
32.  
33.  
34.  
 
 
 
35.  
36.  
37.  
 
 
 
38.  
39.  
40.  
 
 
 
41.  
 
42.  43.  
 
 
 
 
44.  
 
 
45.  
 
46.  
 
 
47.  
48.  
49.  
 
50.  
 
 
 
 
  
N
H
O
CH
3
H
NH
2
OH H
HO OH
OH H
O
H H
3
CO H H
3
CO
CH
3
H
H H
3
C
OH
H
OH
H O
Cl
Cl
H
H Cl
H
H
Cl
Cl
H
H
Cl
Cl
H
Cl
H
Cl
Cl
H
H Cl
Br
H
H
OH
OH
OH
OH
OH
CH
3
OH
H
OH
H
OH
OH
H
H
T
One chiral 
carbon => 
chiral 
molecule
Two common attachments => achiral
Plane of symmetry  => achiral
Two common attachments => achiral
Be able to rotate in order to 
better visualize planes of 
symmetry or lack thereof
Page 3


	 1	
Organic Chemistry I    Test 2  Extra Stereochemistry Practice Problems 
Page 1:  Designate R/S Page 2:  Chiral or Achiral?   Page 3:  Same, Enantiomer, or Diastereomer? 
 
A.  Designate the R/S configuration for any chiral centers in the following molecules. 
 
1.  
 
2.  3.  
4.  
5.  
 
6.  
7.  
 
8.  
9.  
10.  
 
 
11.  
12.  
13.  
 
 
14.  
15.  
16.  
 
 
17.  
18.  
19.  
 
 
20.  
21.  
22.  
 
 
23.  24.  
25.  
26.  
 
 
27.  
28.  
 29.  
30.    
  
Br H H Br H H
2
N
Br H
HO
H
OH
OH H
HO
OH H
HO
O
NH
2
H
OH
O H
OH
OH
Br H
HO
O O
CH
3
H
O O
CH
3
H
N
H
O
CH
3
H
NH
2
OH H
HO OH
OH H
O
OH H
O
H H
3
CO
CH
3
H
OH H
O
NH
2
H
CH
3
OH H
H
2
N
OH
H
CH
3
Br
CH
3
CH
3
H
H
HO
O
H
NH
2
H
H
NH
2
H
3
C
H
CH
3
CH
3
H
HO
CH
3
CH
3
H
H
CH
3
HO
H
CH
3
H
H
OH
O
H
H
Cl HO
O
H
3
C
H
O
CH
2
OH H
H
HO
HO
H
H HO
H
OH
This one is very hard.
But for each of the 5 chiral C's, the tie-
breaking processes do work.  
The upper-left S is harder than the others.
R,R
R,R, error in movie 
which said R, S.
Priorities:  1.  Heteroatom.         2.  C-with-heteroatom. 
3.  C > CH > CH2 > CH3. 
4.  Proceed down chain until point of difference. 
Really
Hard!
	 2	
 
B.  Identify each of the following molecule as chiral or achiral.  (By circling the chiral ones.)  
Write “meso” where it applies.  (In other words, if it is achiral despite having chiral centers).   
 
31.  
 
 
 
32.  
33.  
34.  
 
 
 
35.  
36.  
37.  
 
 
 
38.  
39.  
40.  
 
 
 
41.  
 
42.  43.  
 
 
 
 
44.  
 
 
45.  
 
46.  
 
 
47.  
48.  
49.  
 
50.  
 
 
 
 
  
N
H
O
CH
3
H
NH
2
OH H
HO OH
OH H
O
H H
3
CO H H
3
CO
CH
3
H
H H
3
C
OH
H
OH
H O
Cl
Cl
H
H Cl
H
H
Cl
Cl
H
H
Cl
Cl
H
Cl
H
Cl
Cl
H
H Cl
Br
H
H
OH
OH
OH
OH
OH
CH
3
OH
H
OH
H
OH
OH
H
H
T
One chiral 
carbon => 
chiral 
molecule
Two common attachments => achiral
Plane of symmetry  => achiral
Two common attachments => achiral
Be able to rotate in order to 
better visualize planes of 
symmetry or lack thereof
	 3	
C.  Mark the relationships between the following structures as either “same”, “enantiomers”, 
or “diastereomers”.    
 
51.          
 
 
52.      
53.          
 
 
54.      
55.          
 
 
56.      
57.             
 
 
58.         
59.           
 
 
60.               
61.           
 
 
62.                  
63.  
 
 
64.  
65.          
 
 
 
66.              
67.        
 
 
 
68.                     
 
69.             
70.              
 
Cl
H
Cl
H
Cl
H
Cl
H
Cl
H
H
Cl Cl
H
H
Cl
Cl
H
Cl
H
H
3
C Cl
H
Cl
H
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
Cl
H
Cl
H
H
Cl
H
Cl
Cl
H
Cl
H
H
Cl
Cl
H
Cl
H
H
Cl
H
Cl
Cl
H
Cl
Cl
H
H
Cl
H
H
Cl
Cl
H
H
Cl
Cl
H
H
Cl
Cl
H
H
Cl
Cl
H
H
Cl
OH
OH
OH
H
OH
H
OH
OH
H
H
OH
OH
With just 
one chiral 
C, if you 
can assign 
R/S for 
both, you 
can tell if 
same or 
different.
chiral => all ? ?ipped => enant achiral => all ? ?ipped => same
chiral => all ? ?ipped => enant
With two 
chiral C's: 
1. orient them 
the same; 
2.  look for 
all flipped 
(mirror) vs 
some flipped 
(not mirror, 
diastereomer)
3.  If mirror, 
check for 
plane of 
symmetry 
(meso, achiral, 
mirror same) 
vs not (chiral, 
mirror is 
enantiomer)