Organic Chemistry Assignment: Isomers, Conformations, and Reactions

This organic chemistry assignment solution addresses a variety of key concepts including IUPAC nomenclature, identification of 1°, 2°, and 3° hydrogen atoms, and the naming of organic compounds. It covers the drawing and identification of cis and trans isomers in cyclohexane derivatives, including their most stable configurations. The solution also includes the construction of potential energy diagrams for conformational analysis, specifically for 1,2-dichloroethane, and the identification of chiral compounds, assignment of (R) and (S) designations, and drawing stereoisomers. Additionally, the assignment covers Fischer projections, the designation of (E) and (Z) isomers, the identification of stereochemical relationships, and the analysis of thalidomide's stereogenic carbons, enantiomer, and optical activity. The assignment provides comprehensive solutions to problems related to isomers, conformations, and stereochemistry.

Assignment 5
1. Answer the following questions:
a. Identify the 1°, 2°, and 3° hydrogen atoms in 3,3,4-
trimethylhexane.
b. Give the IUPAC name for each of the following:
c. The following structures are incorrectly named. Briefly explain
the error and give the correct name for each.

3. For each of the following cyclohexane derivatives, indicate whether
the molecule is a cis or trans isomer, and whether it is in its most
stable configuration. If the molecule is not in its most stable
configuration, draw the most stable configuration you would get if
you “flipped” the ring.

4. The anti conformation of 1,2-dichloroethane, CH2ClCH2Cl, is 4.8
kJ·mol–1 more stable than the gauche form. The two energy barriers

(relative to the energy of the gauche form) for the C—C bond
rotation are 21.5 kJ mol–1 and 38.9 kJ mol–1.
Construct a graph of potential energy versus angle of rotation
(similar to Figure 2-13 in your textbook) for 1,2-dichloroethane.
Show the energy differences on your graph. Draw a Newman
projection formula to indicate the conformation present at each
maximum and minimum on the graph.

5. For each of the nine compounds listed below, complete the
following:
a. List those that are chiral.
b. Indicate the asymmetric carbon atom(s) in each of the
molecules you identify as chiral in a).
c. Draw one of the stereoisomers of each of the chiral molecules
in part a) and assign it the correct (R) or (S) designation.
iv) 2-methylheptane
v) 3-methylheptane
vi) 4-methylheptane
vii) 1,1-dibromopropane
viii) 1,2-dibromopropane

6. What are all the stereochemical relations (identical, enantiomers,
diastereomers) of the four molecules for which the Fischer
projection formulas are given below (e.g., i and ii are _____; i and iii
are_____, etc.)? Assign absolute configurations to each asymmetric
carbon.
6. a. Draw a structural formula for each of the following:
i. (E)-3-bromo-2-pentene
ii. (Z)-3,5R-dichloro-3-heptene
iii. cis-1-fluoro-3-methyl-1-butene
b. Designate each of the following as (E) or (Z).
i) ii)

7.Shown below are structural diagrams for five pairs of molecules. From
the list of five terms (enantiomers, diastereomers, conformers,
constitutional isomers, identical), choose the single term that
best describes each pair. Note that a term may be used more than
once if necessary.

7. Assume the drug thalidomide shown below has a specific rotation
of [α]D = 59°, a melting point of 271°C, and is insoluble in benzene.
Thalidomide
a. Label any stereogenic carbons in this molecule and
determine whether they are (R) or (S).
b. Clearly draw the structure of the enantiomer of thalidomide.
c. Based on what you know, is it possible to predict the specific
rotation, melting point, and solubility in benzene of the
enantiomer? Explain.
d. What would be the optical activity (if any) of a racemic
mixture of (+) and
(–) thalidomide?
e. Which term, levorotatory or dextrorotatory would best
describe the optical activity (if any) of a 1:2 mixture of (R) : (S)
thalidomide?