chapter 2: alkanes 2.pdf · Ðc4h9 methyl ethyl butyl prefix suffix meth-eth-but--yl group formula...
TRANSCRIPT
Chapter 2: Alkanes
Alkanes from Carbon and Hydrogen
•Alkanes are carbon compounds that contain only single bonds.
•The simplest alkanes are hydrocarbons – compounds that contain only carbon and hydrogen.
•Hydrocarbons are used mainly as fuels, solvents and lubricants:
# of carbons boiling point range Use
1-4
5-6
6-12
12-15
15-18
16-24
<20 °C
30-60
60-90
85-200
200-300
>400
300-400
6-7
fuel (gasses such as methane, propane, butane)
solvents (petroleum ether)
solvents (ligroin)
fuel (gasoline)
fuel (kerosene)
fuel (heating oil)
lubricating oil, asphalt
C C C C H
H
H
H
H
H
H
H
H
H
C C C C C
H
H
H
CH2
H
H
H
H
H
H
CH3
CH3
H C C
C
C
C
H
H
H
H
H H
H
H
H
H
Hydrocarbons
CH4
C2H6
C3H8
C4H10
methane
ethane
propane
butane
C6H14
C7H16
C8H18
C9H20
C10H22
hexane
heptane
octane
nonane
decane
Prefix Suffix
meth-
eth-
prop-
but-
hex-
hept-
oct-
non-
dec-
-ane
-ane
-ane
-ane
-ane
-ane
-ane
-ane
-ane
Formula Name Structure
H
C
H
HH
H3C CH3
C5H12 pentanepent- -ane
Hydrocarbons
CH4
C2H6
C3H8
C4H10
methane
ethane
propane
butane
Prefix Suffix
meth-
eth-
prop-
but-
-ane
-ane
-ane
-ane
Formula Name Structure
H3C C CH3
H
H
H3C C C CH3
HH
H H
H
C
H
HH
or
or
H
C
H
CH H
H
H
C4H10 butane?but- -ane H3C C CH3
CH3
H
or
CH4
C2H6
C3H8
C4H10
methane
ethane
propane
butane
Prefix Suffix
meth-
eth-
prop-
but-
-ane
-ane
-ane
-ane
Formula Name Structure
H3C C CH3
H
H
H3C C C CH3
HH
H H
H
C
H
HH
or
or
H
C
H
CH H
H
H
C4H10 but- -ane H3C C CH3
CH3
H
or
Hydrocarbons
iso-butane
Hydrocarbons
C4H10 butane
Prefix Suffix
but- -ane
Formula Name Structure
H3C C C CH3
HH
H H
or
C4H10 iso-butanebut- -ane H3C C CH3
CH3
H
or
C5H12 pentanepent- -ane H3C C C C
HH
H H
H
H
CH3 or
H3C C C C
CH3H
H H
H
H
H
H C C C
CH3H
H CH3
H
H
H
or
or
C5H12 iso-pentanepent- -ane
C5H12 iso-pentane???pent- -ane
HydrocarbonsHydrocarbons
C4H10 butane
Prefix Suffix
but- -ane
Formula Name Structure
H3C C C CH3
HH
H H
or
C4H10 iso-butanebut- -ane H3C C CH3
CH3
H
or
C5H12 pentanepent- -ane H3C C C C
HH
H H
H
H
CH3 or
H3C C C C
CH3H
H H
H
H
H
H C C C
CH3H
H CH3
H
H
H
or
or
C5H12 iso-pentanepent- -ane
C5H12 neo-pentanepent- -ane
HydrocarbonsHydrocarbons
IUPAC System of Naming Organic Compounds
pentaneH3C C C C
HH
H H
H
H
CH3
H3C C C C
CH3H
H H
H
H
H
H C C C
CH3H
H CH3
H
H
H
2-methylbutane
2,2-dimethylpropane
1. Find the longest carbon chain
2. Name all the atoms (other than H) not in the longest chain as groups
3. Number groups from the end of the chain closest to the first group
4. List multiple groups in alphabetical order,
1
2
3
4
5
Longest chain: pentane
Groups: none
IUPAC Name
12
34 Longest chain: butane
Groups: one methyl
12
34
not:
not: 3-methylbutane
12
3Longest chain: propane
Groups: two methyls
C4H10 butane
Prefix Suffix
but- -ane
Formula Structure
H3C C C CH3
HH
H H
or
C4H10 iso-butanebut- -aneH3C C CH3
CH3
H
C5H12 pentanepent- -ane H3C C C C
HH
H H
H
H
CH3
H3C C C C
CH3H
H H
H
H
H
H C C C
CH3H
H CH3
H
H
H
C5H12 pent- -ane
C5H12 pent- -ane
Hydrocarbons
IUPAC Name
2-methyl butane
2,2-dimethylpropane
IUPAC System of Naming Organic Compounds
–CH3
–C2H5
–C4H9
methyl
ethyl
butyl
Prefix Suffix
meth-
eth-
but-
-yl
Group Formula Name Structure
C C C CH3
HH
H H
H
C
H
H
or
H
C
H
C H
H
H
-yl
-yl
H
H
–C3H7 propylprop-C C CH3
H
H
or-yl
H
H
–C3H7 iso-propyliso-prop-H3C C CH3
H
or-yl
Abbreviation
–Me
–Et
–Pr
–Bu
–iPr
Naming Branches as Groups
Naming Branches as “Groups”
–C4H9
sec-butyl
Group Formula Name Structure
–C4H9
iso-butyl
–C4H9 tert-butyl
Other Groups We May Encounter
–C5H11neo-pentyl
–F
–Cl
–Br
–I
bromo
fluoro
chloro
iodo
–F
–Cl
–Br
–I
Group Formula Name Structure
Naming Branches as “Groups”
Structural IsomersHow many structural isomers – compounds with the same chemical formula but differentconnectivity – are there with the formula C7H16?
Structural IsomersHow many structural isomers – compounds with the same chemical formula but differentconnectivity – are there with the formula C7H16?
CH3
CH3
CH3 CH3
CH3
CH3
IUPAC Name
1
2
3
4
5
12
34
5
1
2
3
4
5
2,2-dimethylpentane
2,4-dimethylpentane
H3C
CH3
1
23
4
5
1
23
4
5
3,3-dimethylpentane
3-methylhexane
3-ethylpentane
1
2
34
5 6
–
––
–
–
CH3
CH3
12
34
52,3-dimethylpentane
IUPAC Name
2-ethylpentane
CH3
CH3
1
2
3
4
5
6
7heptane
12
3
4
5
6
1
23
4
5
6
2-methylhexane
3-methylhexane
12
3456
CH3
1
2
34
5
6
–
CH3
1
2
34
5
6–
––
–
–
4-methylhexane
3-methylhexane
1
2
3
4
2,2,3-Trimethyl-butane
H3C– methyl
Group Formula Name Structure
H
C
H
H
Abbreviation
–Me
Methyl & Ethyl Compounds
H3C–H
H3C–OH
H3C–NH2
H3C–F
H3C–Cl
H3C–Br
H3C–I
H3C–CN
H3C–SH
methane
methyl alcohol (methanol)
methylamine (aminomethane)
methyl fluoride (fluoromethane)
methyl chloride (chloromethane)
methyl bromide (bromomethane)
methyl iodide (iodomethane)
methyl cyanide (cyanomethane, acetonitile)
methanethiol (methyl mercaptan)
H5C2– ethyl
H
C
H
C H
H
H
–Et
H5C2–H
H5C2–OH
H5C2–NH2
H5C2–F
H5C2–Cl
H5C2–Br
H5C2–I
H5C2–CN
H5C2–SH
ethane
ethyl alcohol (ethanol)
ethylamine (aminoethane)
ethyl fluoride (fluoroethane)
ethyl chloride (chloroethane)
ethyl bromide (bromoethane)
ethyl iodide (iodoethane)
ethyl cyanide (cyanoethane, proprionitile)
ethanethiol (ethyl mercaptan)
Methyl and Ethyl Compounds
H3C– methyl
Group Formula Name Structure
H
C
H
H
Abbreviation
–Me
Methyl & Ethyl Compounds
H3C–H
H3C
H3C
H3C
methane
methyl cation
methyl radical
methyl anion
H5C2– ethyl
H
C
H
C H
H
H
–Et
C H
H
H
C
HH
H
C
HH
H
H5C2–H
H3C–CH2
H3C–CH2
H3C–CH2
ethane
ethyl cation
ethyl radical
ethyl anion
C H
H3C
H
C
HH3C
H
C
HH3C
H
Methyl and Ethyl Compounds
Group Formula Name StructureAbbreviation
prop-
H7C3–iso-prop-
–Pr
–iPr
H7C3– C C CH3
H
H
H
H
H3C C CH3
H
or
or
Propyl Compounds
propyl alcohol (1-propanol)
propyl amine (1-aminopropane)
propyl fluoride (1-fluoropropane)
propyl chloride (1-chloropropane)
propyl bromide (1-bromopropane)
propyl iodide (1-iodopropane)
isopropyl alcohol (isopropanol; 2-propanol)
isopropyl amine (2-aminopropane)
isopropyl fluoride (2-fluoropropane)
isopropyl chloride (2-chloropropane)
isopropyl bromide (2-bromopropane)
isopropyl iodide (2-iodopropane)
OH
NH2
F
Cl
Br
I
12
3HO
H2N
F
Cl
Br
I
1
23
Propyl Compounds
Structural Isomers of C7H16
Cycloheptane contains two fewer hydrogens than heptane. They are not structural isomers.
12
3
4
5
67 heptane
What if we attatch the two ends together?
cycloheptane
12
3
45
6
7
H2C CH2
CH2
CH2
H2C
H2C
H2C
C7H14
Cycloalkanes
cyclopropane
cyclobutane
cyclohexane
cycloheptane
cyclooctane
Compound Name Structure
cyclopentane
cyclopropyl
cyclobutyl
cyclohexyl
cycloheptyl
cyclooctyl
cyclopentyl
Group Name Structure
Cycloalkanes
Naming Cycloalkanes
The above compounds are not structural isomers. Their connectivity is identical. They are stereoisomers – compounds thatdiffer in how substituents are arranged in space
Unlike "floppy" chains, rings have an additional consideration for multiple substitutions:
Me
H
H
H
Me
H
"flat" 1,2-dimethylcyclopropane
Me Me
H
H
Me
H
H
"3-D" 1,2-dimethylcyclopropane
These are different compounds! They cannot be interconvertied by bond rotation.
Me
"3-D" 1,2-dimethylcyclopropane
Me
H
H
H
Me
H
Me
H
H
Me
H
H
cis-1,2-dimethylcyclopropane trans-1,2-dimethylcyclopropane
cis – substituents on same side (of the ring)
trans – substituents on opposite sides (of the ring)
IUPAC Naming of Rings
How can we represent cis/trans isomers in a flat drawing?
Me
H
H
H
Me
H
Me
H
H
Me
H
H
cis-1,2-dimethylcyclopropane trans-1,2-dimethylcyclopropane
Me
Me
Me
Me
A solid wedge means the bond is pointing "up" and out of the page
A dashed wedge means that the bond is pointing "down" and into the page
Naming Cycloalkanes
IUPAC Naming of Rings
cis-1,2-dimethylcyclopropane
Me
Me
Me
H
H
Me
H
H
Me
Me
H
Me
H
H
Me
H
Don't let the wedges and dashes confuse you:
cis-1,2-dimethylcyclopropane
Me
Me
Me
Me
These are the same compound!
Flip over 180°
Naming Cycloalkanes
3-Dimensional Structure/VSEPR Theory
X
X
X
A
XA = any atom
X = any substituent (atom or lone pair)
X
X
X
A
X
H
H
N
H
H
H
O
H
H
H
C
H
F
F
F
B
F
109°
Atoms place substituents as far appart as possible:
tetrahedral electron-domain geometries
A dashed wedge means: the substituent is behind the plane of the paper
A solid wedge means: the substituent is in front of the plane of the paper
3-Dimensional Structure
C C
H
H
H
H
H
H H
CC
HHH
HH
H
H
H
H
C
H
C
H
"flat" ethane
each carbon is tetrahedral
"3-D" ethane
wedge/dash depiction of ethane
H
HH
H
HH
H
H
H
H
HH
C C
H H
H H
H H
The Conformation of Ethane
H
CC
HHH
HH
If we look down the C–C bond axis, we get a different perspective:
C
H
HH
H
HH
H
CC
HHH
HH
But there is free rotation around single (!) bonds:
these hydrogens are in the same plane
these hydrogens are in the same plane
We can use a Newman Projection to depict this view:
Front atom appears at vertex here
The large circle is a stylized representation of the back atom
Newman Projection
H
HH
H
HH
The "staggered" conformationThe "eclipsed" conformation
3-Dimensional Structure
3-Dimensional Structure
Molecules that differ by only rotations around single bonds are conformational Isomers.
H
H
H
H
HH
C C
H H
H H
H H
H
CC
HHH
HH
these hydrogens are in the same plane
these hydrogens are in the same plane
H
HH
H
HH
The "staggered" conformationThe "eclipsed" conformation
H
HH
H
HH
The energy minimum
The staggered conformation is the lowest energy conformation
H
H
H
H
HH
The energy maximum
The elclpsed conformation is the highest energy confornation
How can these molecular shapes arise from bonding between the available orbitals?
180°
C NH3C
Place substituents as far appart as possible:
Molecule is linear
H
H
H
C
H
109°
F
F
B
F
120°
Molecule is trigonal planar
Molecule is tetrahedral
2s 2px
2nd row valence orbitals
2py 2pz
H3CCN
BF3
CH4
3-Dimensional Structure
Hybridization
C C
this side gets bigger and 50% more spherical this side gets smaller and
50% more spherical
mixingCand
2s
2px
2 unhybridized orbitals 2 sp-hybridized orbitals
Only "X"-directionality; 50% s-like and 50% p-like
180°
C NH3C
Molecule is linear
2s 2px
2nd row valence orbitals
2py 2pz
H3CCN
C NH3CC NH3C
sp-orbitals on the central carbon atom the !-bond formed by sp-orbital overlap
C NH3C
"-bonding in the triple bond
CC
this side gets bigger and 33% more spherical this side gets smaller and
33% more spherical
mixing and
2s
2px
3 unhybridized orbitals3 sp-hybridized orbitals
Only "X" and "Y"-directionality; 33% s-like and 67% p-like
2s 2px
2nd row valence orbitals
2py 2pz
F
F
B
F
120°
Molecule is trigonal planar
BF3
2py
C
C
and
B
F
F
All 3 sp2-orbitals on the boron atom The !-bonds between boron and fluorine
F B
F
F
F
Hybridization
mixing
All 4 unhybridized orbitals Each orbital has "X", "Y" and "Z"-directionality and are 25% s-like and 75% p-like
2s 2px
2nd row valence orbitals
2py 2pz
All 4 sp3-orbitals on the carbon atom The !-bonds between carbon and hydrogen
H
H
H
C
H
109°
Molecule is tetrahedral
CH4
H
H
H
C
H
H
H
H
C
H
2s 2px 2py 2pz
Hybridization