Chemistry
205 0 “Introduction
to
Organic
Chemistry”
Fall
Semester
2011
Dr.
Rainer
Glaser
Examination #1
“Bonding, Alkanes, Alkenes & Alkynes”
Wednesday, September 14, 2011, 10 – 10:50 am
Name:
Answer Key
Question 1. Atomic Structure & Lewis Structures
20
Question 2. Nomenclature of Alkanes, Alkenes & Alkynes
20
Question 3. Conformations of Alkanes
20
Question 4. Reactions of Alkanes
20
Question 5. Reactions of Alkenes & Alkynes
20
Total
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1
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100
Question 1. Atomic Structure and Lewis Structures. (20 points)
(a) Nitrogen atom has 7 electrons. Provide the electron configurations of nitrogen in its ground state.
Use the “line format” (one short line for each AO) to indicate the number of electrons in atomic orbitals
1s, 2s, 2px, 2py, and 2pz and indicate the spin (up or down) of the electrons. (2 points)
(b) Provide the approximate value of the ∠(H−N−H) angle in ammonia, NH3, and state the hybridization
at N in ammonia. (2 points)
ca. 109.5°, sp3 hybridization
(c) Draw complete Lewis structures of NO (neutral) and NO+ (cation). Draw all lone pair, show
unpaired electrons and indicate formal charges. (6 points)
NO
NO+
(d) Draw structural formulas for all possible isomers with the formula C3H6Cl2. (4 points)
An earlier version of the AK incorrectly showed ClCH2-CH2Cl-CH3 (9/23/11).
(e) Draw the three most important resonance forms of nitrate ion, NO3-. Draw complete Lewis
structures (all lone pairs, formal charges). Use the correct “resonance arrow” between the resonance
forms. (6 points)
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2
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Question 2. Nomenclature of Alkanes, Alkenes & Alkynes. (20 points)
(a) Draw the abbreviated structural formula of
2,2,3-trimethylbutane. Draw all C–C bonds; you
may abbreviate methyl groups as CH3, a.s.o. (4
points)
(b) Draw the line-segment formula of 5-fluorocyclo-1,3-hexadiene. (4 points)
(c) Give the IUPAC name of the structure shown.
Do not worry about configuration. (4 points)
Name:
(trans- or E-) 2,3-dichloro-2-pentene
(d) Give the IUPAC name of the structure shown.
(4 points)
Name:
cyclopentadiene, cyclo-1,3-pentadiene
(e) Give the IUPAC name of the structure shown.
(4 points)
Name:
1-pentyne, 1-pentine
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3
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Question 3. Conformations of Alkanes. (20 points)
(a) Provide a perspective drawing of
the
staggered conformation of ethane. (4 points)
Perspective Drawing
(b) Provide a Newman projection of the staggered
conformation of ethane. (4 points)
Newman Projection
(c) Provide a perspective drawing of the trans
conformation of butane. (4 points)
Perspective Drawing
(d) Provide a Newman projection of the gauche
conformation of 1,2-dichloroethane. (4 points)
Newman Projection
(e) Circle the more stable
conformation of the molecule
shown. The more stable structure
adopts the __chair_ conformation
and the substituent prefers to be in
the ____equatorial___ position. (4
points)
Circle left
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4
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Question 4. Reactions of Alkanes. (20 points)
(a) Provide the stoichiometry of the incomplete combustion of ethane to CO. (3 points)
2 H3C−CH3 + 5 O2 → 4 CO + 6 H2O
(b) Provide the structures of the three products of monochlorination of 2,2-dimethylbutane. Circle the
product that will be formed in the largest amount. (6 points)
major, circle this
(c) Provide the structures of the two possible products of tetrachlorination of ethane. (No need to
indicate conformation; we are only interested in connectivity.) (4 points)
(d) Provide the structure of the major product of
monobromination of 2,3-dimethylbutane. (4 points)
(e) Provide the reaction equation of the first propagation reaction of the radical chain chlorination of
ethane (an H-abstraction). (3 points)
H3C−CH2−H
+
Cl•
→
H3C−CH2•
+
H−Cl
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Question 5. Reactions of Alkenes and Alkynes. (20 points)
(a) For the electrophilic addition reaction of cis-2-butene with hydrogenbromide (H−Br), draw linesegment structures of the substrate and the product. Provide the product’s IUPAC name. (3 points)
2-bromobutane
(b) Provide abbreviated structural drawings (show C−C and C−Br bonds; do not show C−H bonds, write
CH, CH2, CH3) of the two products of the electrophilic addition reaction of 2-methyl-2-butene with
H−Br. Circle the Markovnikov product, i.e., the one formed in larger amounts. (4 p.)
major
(c) The Pt-catalyzed addition of hydrogen (H2) to 1,2-dimethylcyclopentene forms 1,2-dimethylcyclopentane. This addition is remarkable in that the two methyl groups end up on ___________________
(the same face, opposite faces) of the cyclopentane. This outcome occurs because the two H atoms are
supplied from ______________________ (the same face, opposite faces) of the cyclopentene in this
___________________ (homogeneous, heterogeneous) hydrogenation reaction. (3 points)
(d) Provide the structures of the
two products of the ozonolysis
of 2-pentene (O3; Zn, H+). (4 p.)
(e) Consider the Diels-Alder
reaction of butadiene and 1,1,2,2tetracyanoethene. Draw the
abbreviated structural formulas of
both substrates and of the product;
show C−C and C−CN bonds; do
not show C−H bonds; write C,
CH, CH2, CH3, CN. (6 points)
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6
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