Alicyclics
Aliphatic compounds containing rings,
cycloalkanes, cycloalkyl halides,
cycloalkyl alcohols, cyclic ethers,
cycloalkenes, cycloalkadienes, etc.
Cycloalkanes
H2C
CH2
H2C
H2C CH2
H2C CH2
H2
H2C C
CH2
H2C C
H2
cyclopropane cyclobutane cyclopentane
H2C
H2C
H2
C
C
H2
CH2
CH2
cyclohexane
CH3
H3C
CH3
methylcyclopentane
1,1-dimethylcyclobutane
Br
Br
Br
Br
Br
trans-1,2-dibromocyclohexane
Br
H H
O O
HO
OH
HO
OH
cis-1,2-cyclohexanediol
cycloalkenes
3
4
2
5
1
6
cyclopentene
3-methylcyclohexene
1,3-cyclobutadiene
bicyclo[2.2.2]octane
bicyclo[3.2.0]heptane
OH
CH2CH3
O
cyclohexanol
cyclohexyl alcohol
ethyl cyclopentyl ether
Cycloalkanes, syntheses:
A. Modification of a ring compound:
1. reduction of cycloalkene
2. reduction of cyclic halide
a) hydrolysis of Grignard reagent
b) active metal & acid
3. Corey House
B. Ring closures
A. Modification of a cyclic compound:
H2, Ni
Br
Br
Sn, HCl
Mg; then H2O
Li
Br
CuI
Li
2
+ CH3CH2-Br
must be 1o
Corey-House
CuLi
CH2CH3
B. ring closures
CH2=CH2
+
CH2CO, hv 
Br-CH2CH2CH2CH2CH2-Br + Zn 
etc.
cycloalkanes, reactions:
1. halogenation
Cl2, heat
Cl
2. combustion
3. cracking
4. exceptions
+ HCl
exceptions:
H2, Ni, 80o
CH3CH2CH3
Cl2, FeCl3
Cl-CH2CH2CH2-Cl
H2O, H+
CH3CH2CH2-OH
conc. H2SO4
CH3CH2CH2-OSO3H
HI
CH3CH2CH2-I
exceptions (cont.)
+
??????????
H2, Ni, 200o 
CH3CH2CH2CH3
internal bond
deviation
heat of
angles
from 109.5
combustion
60o
-49.5o
166.6
90o
-19.5o
164.0
108o
-1.5o
158.7
Cyclopropane undergoes addition reactions that other
cycloalkanes and alkanes do not. This is because of
angle strain in the small ring. Because the bond angles
are less than the optimal 109.5o for maximum overlap,
the bonds are weaker than normal carbon-carbon single
bonds and can be added to.
Cyclobutane has angle strain that is less than that for
cyclopropane, reacts with H2/Ni at a higher temperature,
but does not react like cylcopropane in the other
exceptional reactions.
internal bond
deviation
heat of
angles
from 109.5
combustion
60o
-49.5o
166.6
90o
-19.5o
164.0
108o
-1.5o
158.7
120o
+11.5o
157.4
128.5o
+19o
158.3
135o
+25.5o
158.6
Cyclohexane does not have
any angle strain! It isn’t a flat
molecule. By rotating about
the carbon-carbon bonds, it can
achieve 109.5o bond angles.
conformations of cyclohexane
chair
boat
twist boat
The chair conformation of cyclohexane is free of
both angle strain and torsional strain (deviation
from staggered). This is the most stable
conformation.
The boat conformation is free of angle strain, but has a
great deal of torsional strain (eclipsed). To relieve the
strain, it twists slightly to form the twist boat:
a
a
e
e
a
e
e
e
a
a
e
a
a = axial positions in the chair conformation
e = equatorial positions
CH3

CH3 in axial position
H3C
CH3 in equatorial position
is more stable
H OH
HO
HO
HO
H
H
OH
H
OH
beta-D-glucose
all groups equatorial
more stable
H
HO
H
H
CHO
OH
H
OH
OH
CH2OH
H OH
HO
HO
HO
H
H
H
OH
OH
alpha-D-glucose
one group forced to be axial
Cycloalkenes, syntheses:
A. Modification of a ring compound:
1) dehydrohalogenation of an alkyl halide
2) dehydration of an alcohol
3) dehalogenation of vicinal dihalides
(B. Ring closures)
Cl
OH
KOH(alc)
H+, Δ
cyclohexene
Br
Br
Zn
Cycloalkenes, reactions:
1. addition of H2
10. hydroboration-oxid.
2. addition of X2
11. addition of free radicals
3. addition of HX
12. polymerization
4. addition of H2SO4
13. addition of carbenes
5. addition of H2O,H+
14. epoxidation
6. addition of X2 + H2O
15. hydroxylation
7. dimerization
16. allylic halogenation
8. alkylation
17. ozonolysis
9. oxymerc-demerc.
18. vigorous oxidation
H2, Pt
Br2, CCl4
Br
Br
trans-1,2-dibromocyclohexane
H2C
H2C
H2
C
C
H2
CH3
C
CH
+ HBr
H2C
H2C
3o carbocation
Br
H2
C
C
H2
CH3
C
CH2
H2
CH3
C
H2C
C Br
H2C
CH2
C
H2
HBr
H2SO4
H2O, H+
Br
OSO3H
OH
Markovnikov orientation
Br2 (aq.)
OH
Br
H+, dimer.
+
HF, 0o
+
H2O, Hg(OAc)2
NaBH4
OH
Markovnikov
(BH3)2
H2O2, NaOH
OH
anti Markovnikov
HBr, peroxides
Br
polymerization
n
CH2CO, hν
Peroxybenzoic acid
O
KMnO4
OH
cis-1,2-cyclohexanediol
OH
HCO3H
OH
trans-1,2-cyclohexanediol
OH
Br2, heat
Br
O3
H2O,Zn
KMnO4, heat
O=CHCH2CH2CH2CH2CH=O
HO2CCH2CH2CH2CH2CO2H
stereoselective
Br2
Br
anti
KMnO4
Br
HO
syn
OH
HCO3H
HO
anti
OH
cyclic alcohols, halides, ethers as expected:
PBr3
OH
Br
Na
ONa
OH
HO
CH3COOH +
H+
H3C
NaOCl
OH
O
O
C
O
Br
NaOH
2o alkyl halide => E2
Cl
O
MgCl
Mg
conc. HI, heat
2
O
O
1,4-dioxane
H2O
conc. HBr, heat
I
2 Br-CH2CH2-Br
Alicyclic compounds are chemically
like their open chain analogs. The
exceptions are for small ring
compounds where angle strain may
give rise to reactions that are not
typical of other molecules.
Epoxides:
H2C CH2
O
H2C CH CH3
O
ethylene oxide
propylene oxide
(oxirane)
(methyloxirane)
O
cyclopentene oxide
Synthesis:
C6H5CO3H
O
cis-2-butene
β-butylene oxide
epoxides, reactions:
1) acid catalyzed addition
H2C CH2
O
H2C CH2
O
H2C CH2
O
H2O, H+
CH3CH2OH, H+
HBr
OH
CH2CH2
OH
OH
CH3CH2-O-CH2CH2
OH
CH2CH2
Br
2. Base catalyzed addition
H2C CH2
O
OH
CH2CH2
OH
NaOH, H2O
H2C CH2 NaOCH2CH3
O
CH3CH2OH
H2C CH2
O
H2C CH2
O
NH3
CH3CH2-O-CH2CH2-OH
H2N-CH2CH2-OH
1. CH3CH2MgBr
2. H2O
CH3CH2CH2CH2-OH
mechanism for acid catalyzed addition to an epoxide
1)
2)
3)
C C
O
+ H
C C
O
H
ZH
C C
OH
RDS
C C
O
H
ZH
C C
OH
+ :ZH
Z
C C
OH
+ H
mechanism for base-catalyzed addition to an epoxide:
RDS
1)
2)
C C
O
Z
C C
O
+ Z
+ HZ
Z
C C
O
Z
C C
OH
+ Z
acid catalyzed addition to unsymmetric epoxides?
H3C CH CH2
O
+ H2O, H+
OH
 CH3CHCH2
OH
which oxygen in the product came from the water?
18OH
H3C CH CH2
O
+ H218O, H+ 
CH3CHCH2
OH
H3C CH CH2 + CH3OH, H+
O
H3C CH CH2
O
+ HBr

CH3
O
 CH3CHCH2
OH
Br
CH3CHCH2
OH
Base?
18OH
H3C CH CH2
O
+ Na18OH, H218O  CH3CHCH2
OH
H3C CH CH2
O
OCH3
+ CH3OH, CH3ONa  CH3CHCH2
OH
H3C CH CH2
O
+ NH3
NH2
 CH3CHCH2
OH
Acid:
H3C CH CH2
O
Z
+ HZ  CH3CHCH2
OH
Base:
H3C CH CH2
O
Z
+ Z-, HZ  CH3CHCH2
OH
“variable transition state”
acid:
Z
δ+C — C —
—
‡
OH
δ+
base:
‡
Z
—C—C—
O
δ-
Bond breaking is
occurring faster than
bond making, making the
carbon slightly positive.
C δ+ : 3o > 2o > 1o
Bond breaking is occurring
at the same time as bond
breaking, there is no charge
on the carbon. Steric
factors are most important:
1o > 2o > 3o
Acid:
H3C CH CH2
O
Z
+ HZ  CH3CHCH2
OH
Cδ+: Z to 2o carbon
Base:
H3C CH CH2
O
Z
+ Z-, HZ  CH3CHCH2
OH
steric factors: Z to 1o carbon