UAU Chemistry Molecules Question

CHM2001 (A.B. Brown)Name: ____________________________
Exam #2 version 1
(please print)
October 1, 2021
50 minutes, 100 points
Instructions:
(1) Show your work; be logical.
(2) Use of molecular models is encouraged; otherwise this exam is closed-book.
(3) There are five problems.
X
Scoring:
Problem
X
Possible
Earned
Equatorial preferences:
1
20
X
(kcal/mol)
2
16
F
0.2
3
20
Cl
0.5
4
20
Br
0.6
5
24
OH
1.0
100
CH3
1.7
Total
Names.
(1) Name each compound shown using the method specified. Denote geometric identity (if any)
using an an appropriate descriptor.
(a) Quasi-systematically (common names of alkyl groups may be used).
H
H
(b) Systematically.
Cl
Cl
Cl
Cl
(c) Systematically.
I
(d) Systematically.
F
Br
(e) Systematically.
H
H
Rings.
(2) (a) Consider these two compounds.
Box the more stable of the two compounds above. Concisely, why is this compound more
stable than the other one? (Hint: consider the bold rings.)
(b) Consider these three compounds.
Box the most stable of these, and circle the least stable.
Concisely justify the stability order you have just predicted.
More Rings.
(3) Consider compound 1.
Cl
Cl
1
Hint: what’s this?
Hint: not chlorine.
Hint: not H.
(a) Draw the two chair conformations of compound 1 (related by a ring flip). In each
conformation, indicate which substituents are axial and which are equatorial.
(b) Which of the conformations above is more stable, and (energetically) by how much?
(Equatorial preferences for individual substituents are tabulated on the front cover.)
Even More Rings.
(4) Consider compounds 2 and 3.
CH3
H
H
CH3
2
H
H
3
H
H
H
H
(a) Draw the most stable conformation of each molecule in the correspondingly labelled space
below. (Hint: All three rings are chairs; choose a view that shows them as such.)
2:
3:
(b) For each molecule: are there any other conformations in which all three rings are chairs? If
so, draw them; if not, concisely state why not.
2:
3:
(c) Which molecule is more stable, 2 or 3? Concisely, why?
Halogenation.
(5) (a) [16 pts] Assume that the relative reactivities of primary, secondary, and tertiary H’s
toward bromination are 1, 80, and 1600 respectively. Draw the products that will form from
monobromination of compound 4, and predict the mol ratio of these products.
4
(b) [8 pts] Assume that free-radical “sulfenylation” of compound 5 (note: different from 4) gives
products A-C in the mol ratio shown.
SR
SR
RS SR
(CH3CH2)3CH
+
heat
5
A
Mol Ratio:
+
SR
9
B
42
C
10
Calculate the relative reactivities of primary, secondary, and tertiary H’s toward
“sulfenylation”.