Alkene geometry-ANSWER KEY
Chemistry 260
1.
Organic Chemistry
The answer is 2.
The two carbons of the double bond are sp2 hybridized (planar). Therefore,
all carbons lie in the same plane.
H 3C
CH3
C
C
H 3C
2.
CH3
The answer is 4.
CH2CH3
CH3CH C
1
2
3 CH2CH3
4
5
3-ethyl-2-pentene
3.
Give the IUPAC name of 2-ethyl-1-butene
4
3
CH3CH2
2 1
H
C C
H
CH3CH2
4.
Give the structural formula of:
(a) 2,3-dimethyl-2-butene
CH3
(b) 2,3-dimethyl-2-butanol
OH
CH3
C
C
CH3
CH3C
CH3
CH3 CH3
(c) 3-chloropropene
H
H
(d) 3-methyl-2-pentanol
CH2Cl
C
OH
C
H
CHCH3
1
CH3CHCHCH2CH3
CH3
5.
(E)-2-pentene
1
CH3
2
C
H
3
C
H
CH2CH3
4
6.
The answer is 1.
5
H
H
H
CH3
H2C CHCH2CH3
H3C
7.
H2C
CH2
H2C
CH2
CH3
H3C
CH2
H3C
H3C
H2C
H2C
H
CHCH3
Give the IUPAC name of:
(a)
cis-3-hexene or (Z)-3-hexene
1
2
CH3CH2
5
4
3
C
6
CH2CH3
C
H
H
(b) trans-2,5-dimethyl-3-hexene or (E)-2,5-dimethyl-3-hexene
CH3
CH3
1
CH
2
H
C
H
3
C
4
5 CH
CH3
CH3
6
2
8. The answer is 2.
2
9. The answer is 1.
2'
H
H
1
H3CH2C
C C
H3 C
H
1'
(Z)
2
11. The answer is 2.
1
Br
H3CH2C
1'
(E)
1
Cl
2'
(Z)
1
2'
Cl
C C
Cl
Cl
1'
(Z)
1'
(Z)
1
Cl
C C
H
CH2CH3
13. The answer is 3.
2'
CO2CH3
H
2'
H
C C
CH2CH3
2
C C
2
2
H3C
12. The answer is 2.
1'
Br
H3C
2'
H
C C
CH2CH3
1
10. The answer is 2.
H
1
1'
Neither – left carbon
has
two
identical
substituents
14.
The answer is 3.
H
H
CH3
C C
C C
H3C
H
H
H
C C
H
H3C
CH3
C C
H
(E,Z)
CH3
H
(Z,Z)
(d) two isomers
CH2CH3
Cl
C C
H
H
C C
H
(a) one isomer
H
H
C C
H3C
(E,E)
15.
H
CH3
H
C C
H
H
3
C C
H
(Z)
CH3
Cl
H
(E)
(b) two isomers
H3C
(e) one isomer
CH3
H
C C
H
CH3
H3CH2C
C C
H
H3C
(Z)
CH2CH3
C C
H
H3C
CH2CH3
(E)
(c) one isomer
H3C
CH3
C C
H3C
16.
H
Give the structural formula of cis-2-methyl-3-heptene
CH3
CH3CH
CH2CH2CH3
C
C
H
17.
H
cis- and trans-Isomers of 1,2-dichloroethene can be isolated because C=C
(σ + π) bonding is quite rigid. For 1,2-dichloroethane, only a single C-C (σ)
bond exists and this is not rigid. Free rotation about the σ bond in 1,2dichloroethane removes any possibility of distinct cis- and trans-isomers:
H
Cl
H
C C
Cl
H H
Cl
Cl
Cl
C C
H
Cl
(E)-1,2-dichloroethene
18.
H
(Z)-1,2-dichloroethene
The answer is 2.
1
H 3C
2'
CH3
C C
H
F
2
1'
(E)
4
H
H
1,2-dichloroethane
(rotation about σ-bond is
easier than about π-bond)
19.
E/Z Isomers are only possible when there is a C=C double bond present in the
molecule.
(a) NO - no double bond present
CH3
(b) NO - only one orientation possible if
triple bond present
H3C C C CH3
H3C C CH3
Cl
(c) NO - double bond present, but
one C has two identical groups
H3 C
(d) YES - two geometric isomers:
H
H
H
H
C C
C C
H
C C
CH3
H
(Z)
(e) YES - two geometric isomers:
2
1'
Cl
F
2
20.
(E)
1
H3CH2C
C C
H
2'
Cl
1
(Z)
(E)
(f) YES - two geometric isomers:
2'
H
F
C C
Cl
1
CH3
1'
CH3
2
H
C C
H
Cl
1'
2
C C
H
(Z)
1'
CH3
2'
H3CH2C
1
(E)
H
2'
Name the following compounds according to the IUPAC rules nomenclature.
Indicate stereochemistry where appropriate.
5
A:
(a) trans-4-isopropylcyclohexanol or trans-4-(1-methylethyl)cyclohexanol.
(b) E-4-bromo-3-fluoro-5-methyl-3-heptene or E-4-bromo-3-fluoro-5methylhept-3-ene. (c) (Z)-3-iodo-5-methyl-3-octene or (Z)-3-iodo-5methyloct-3-ene.
21.
Draw the structure of 2-chloro-1-hexene
22.
Name the following compounds.
Answers:: (a) (E)-5-bromo-4-isopropylhept-3-ene OR (E)-5-bromo-4-isopropyl-3heptene
(b) (E)-3-bromo-2-fluoro-4,6,6-trimethylhept-2-ene OR (E)-5-bromo-4-isopropyl3-heptene
6