Transcript Alkanes - University of Illinois at Urbana–Champaign

Alkanes
CnH2n+2
all C are sp3 hybridized 4  bonds 109.5o
n
1
2
3
4
5
root suffix formula
meth ane CH4
ane C2H6
eth
prop
ane C3H8
but
ane C4H10
pent
ane C5H12
6 hex
7 hept
8 oct
9 non
10 dec
ane
ane
ane
ane
ane
C6H14
C7H16
C8H18
C9H20
C10H22
p
s
atomic orbitals
sp3
Alkanes
London Dispersion Forces
compound
CH4
C2H6
C3H8
C4H10
C5H12
m.w.
16
30
44
58
72
b.p.(Co)
-164
-88.6
-42.1
-0.5
+36.0
n = 1-4 gases
n = 5-15 liquids
n > 15 solids
Alkanes
compound
IMF = q____
1q2
r
m.w.
b.p.
72
36.1
72
27.9
72
9.5
structural isomers
same formula different shape
r  branching
Reactions of Alkanes
Substitution of halogens
h
step 1
step 2
step 3
step 4
.
Cl2  2Cl
.
.
Cl + CH4  CH3 + HCl
.
.
CH3 + Cl2  CH3Cl + Cl
.
.
Cl + Cl  Cl
2
initiation
propagation
propagation
termination
get a mixture of chlorinated methanes
Halogenation of Alkanes
chloromethane

CH3Cl

CH2Cl2 dichloromethane
CHCl3 tri chloromethane
methylene chloride
chloroform
CCl4 tetrachloromethane
carbon tetrachloride


methyl chloride
all liquids at room temperature methane is gas
e- rich Cl increases LDF
dipole moments
Which are soluble in H2O? polar solvent
Nomenclature
1. Pick longest C chain as parent
2. Number C beginning at end with first branch
3. Identify branching substituents
Assign each a number
4. Use commas to separate numbers
hyphens to separate numbers from names
5. Alphabetize substituents
Nomenclature
Structural isomers of C5H12
I.
II.
41
322
233
III.
144
1
I. pentane
II. 2- methylbutane
III. 2,2- di methylpropane
1
2
3
Nomenclature
R = “alkyl” group
1o
primary carbon
2o
secondary carbon
3o
tertiary carbon
4o
quaternary carbon
Nomenclature
“common” names to learn:
H
isopropyl
alphabetized as i
sec- butyl
alphabetized as b
isobutyl
alphabetized as i
tert- butyl alphabetized as b
Nomenclature
1
1
3
2
4
5
6 7
4 3
2 1
2
34 5
6 7
5
6
7
heptane
3 branches
heptane
2 branches
heptane
4 branches
Nomenclature
1
2
34 5
6 7
2- methyl
3- ethyl
4- propyl
5- ethyl
3,5-diethyl
methyl
ethyl
propyl
3,5-diethyl-2-methyl -4-propylheptane
Cycloalkanes
linear alkanes
branched alkanes
CnH2n+2
cycloalkanes closed rings
CnH2n
2
cyclo propane
bond angle = 60o
1
3
tetrahedral angle = 109o
very unstable
Cycloalkanes
cyclobutane
bond angle = 88o
tetrahedral angle = 109o
unstable
Cycloalkanes
cyclopentane
bond angle = 108o
tetrahedral angle = 109o
stable
Cycloalkanes
cyclohexane
predicted bond angle = 120o
tetrahedral angle = 109o
stable
Cycloalkanes geometric isomers
-
cis-1,3-dichlorocyclobutane trans-1,3-dichlorocyclobutane
Optical isomerism
*
C* = Stereocenter
4 different
substituents
bromochloroiodomethane
*
3-methylhexane
*
*
bromocyclopentane
no C*
trans-1,3-dibromocyclopentane
Alkane Summary
1. Alkanes - sp3 hybridized
2. Relatively unreactive
Substitution with halogens
Combustion
3. Non-polar
IMF = London Dispersion Forces
size
structure
4. Free rotation around C-C bonds
conformations
5. Non-cyclic alkanes - structural isomers
6. Cyclic alkanes - geometric isomers
cis-, trans-
7. Alkanes - optical isomers
stereocenters
C*