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Chapter 3 Practice Chem 12A
- The twisted boat conformation of cyclohexane is actually a slightly lower energy conformation than the boat
conformation. Which of the following accurately describes one factor involved in this structural behavior?
A) lower angle strain in the boat
B) higher torsional strain in the twisted boat
C) fewer unfavorable steric factors in the twisted boat
D) increased rotational freedom in the boat
E) lower bond strain in the boat
- What is the major constituent of natural gas?
A) octane B) butane C) propane D) ethane E) methane
- If an acyclic alkane hydrocarbon contains n carbon atoms, how many hydrogen atoms must it also contain?
A) n B) 2n C) n + 2 D) 2n + 2 E) n - 2
- Which of the following statements is a correct description of the most stable conformation of
1,1,3-trimethylcyclohexane?
A) The methyl group at C-3 is equatorial.
B) C
1 is a tertiary carbon and C
C) C-1 is a quaternary carbon and C-3 is a secondary carbon.
D) C-1 is a tertiary carbon and C-3 is a secondary carbon.
E) Both methyl groups at C-1 are equatorial.
- How many methyl groups are present in 2,4-dimethylhexane?
A) 0 B) 2 C) 4 D) 6 E) 8
- Identify the correct IUPAC name for the following structures.
A) 4 - (2-iodo- 1 - methylethyl)- 3 - methylheptane B) 3 - s-butyl- 1 - iodo- 2 - methylhexane
C) 1 - iodo-2,4-dimethyl- 3 - propylhexane D) 2,4-dimethyl- 1 - iodo- 3 - propylhexane
- Assuming a chair conformation, which of the following configurations will always have both methyl groups in
relative axial/equatorial positions?
A) trans-1,3-dimethylcyclohexane B) cis-1,3-dimethylcyclohexane
C) cis-1,2-dimethylcyclohexane D) trans-1,2-dimethylcyclohexane
E) Both B and D are correct. F) Both A and C are correct.
- The structures below are ________.
A) not isomers
B) conformational isomers
C) cis-trans isomers
D) structural isomers
E) both B and D
- Which of the following cycloalkanes exhibits the greatest molar heat of combustion?
A) cyclooctane
B) cycloheptane
C) cyclohexane
D) cyclobutane
E) cyclopropane
- With each structure below drawn in its most stable chair conformation, identify the sequence that ranks the structures in
order of increasing stability.
A) 1 < 2 < 3 B) 2 < 3 < 1 C) 3 < 1 < 2 D) 2 < 1 < 3
- Which of the following statements regarding cyclobutane is correct?
A) The lowest energy conformation of cyclobutane is a planar one in which all of the bond angles is 90°.
B) The lowest energy conformation of cyclobutane is known as the chair conformation.
C) The lowest energy conformation is one in which the bond angles are slightly less than 90° even though this
increases angle strain.
D) The lowest energy conformation is one in which the bond angles are greater than 90° so that angle strain is
significantly reduced.
E) None of the above statements is correct.
- Among the butane conformers, which occur at energy minima on a graph of potential energy versus dihedral
angle?
A) gauche only
B) eclipsed and totally eclipsed
C) gauche and anti
D) eclipsed only
E) anti only
Draw the most stable conformation of trans-1,2-dimethylcyclohexane.
Draw the most stable conformation of cis- 1 - ethyl- 4 - isopropylcyclohexane.
Linear alkanes generally have higher phase transitions than their branched isomers. However, the melting point
of cyclohexane is 6° C while the melting point of hexane is
- 95° C. Briefly suggest a reason why this is.
Draw the most stable conformation of cis- 1 - ethyl- 3 - methylcyclohexane.
View a butane molecule along the C 2
C
bond and provide a Newman projection of the lowest energy
conformer.
- From the perspective of viewing down the C2-C3 bond, draw the Newman projection of the least stable
conformation of 2,3-dimethylbutane.
Provide an acceptable structure for spiro [4.4]nonane.
Draw the most stable conformation of trans-decalin.
By using the appropriate molecular formulas, write a balanced equation which describes the complete
combustion of nonane.
Answer Key
Testname: UNTITLED
1) C
2) E
3) D
4) A
5) C
6) A
7) F
8) D
9) A
10) D
11) C
12) C
13) C
- trans - 1 - bromo- 3 - (tert-butyl)cyclohexane
trimethylhexane
- 2,2,7-trichloro- 4 - ethyl- 6 - isobutyl-7,10-dimethyldodecane
- cis- 1 - isopropyl- 3 - methylcycloheptane
- Cyclohexane is more symmetric molecule and doesn't have as many degrees of freedom or conformational flexibility
as hexane. This allows it to pack in a more regular lattice and has stronger IMFs between the molecules and therefore a
higher boiling point.
