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Hydrocarbons
CxHy
Hydrides of Carbon
C
H
HH
H
Carbonhas fourvalence electrons.Wants to form fourbonds.
Hydrogen has one valenceelectron and wants to form one bond
Methane
C
H
HH
H
Ethane
C
H
CH
H
H
H
H
C
H
CH
H
H
C
H
H
H
H
Propane
C
H
CH
H
H
C
H
H
H
C
H
H
H
Butane
Methane CH4 Ethane C2H6
Propane C3H8 Butane C4H10
Compound Formula Melting Pt. ºC Boiling Pt. ºC
methane CH4 -182.5 -162ethane CH3CH3 -183.3 -88.6n-propane CH3CH2CH3 -187.7 -42.1n-butane CH3(CH2)2CH3 -138.3 -0.5n-pentane CH3(CH2)3CH3 -129.8 36.1n-hexane CH3(CH2)4CH3 -95.3 68.7n-heptane CH3(CH2)5CH3 -90.6 98.4n-octane CH3(CH2)6CH3 -56.8 125.7n-nonane CH3(CH2)7CH3 -53.5 150.8n-decane CH3(CH2)8CH3 -29.7 174.0n-undecane CH3(CH2)9CH3 -25.6 195.8n-dodecane CH3(CH2)10CH3 -9.6 216.3n-eicosane CH3(CH2)18CH3 36.8 343
Ethane Conformations
Staggered Eclipsed
0 60 120 180 240 300 360
Angle of Rotation, degrees
12 kJ
Variation of Energy with Rotation of C-C bond in Ethane
Butane C4H10 n- 2-methylpropaneor isobutane
These two molecules are structural isomers.
They differ in the way their atoms are connected
They have different chemical and physicalproperties.
2-methylpropaneor isobutane
CC
C
C
H
HHH
HH
HH
HH
CH3CH(CH3)CH3
n-hexane
These structures represent differentconformations of n-hexane, not isomers.
n-hexane 2-methylpentane
3-methylpentane4-methylpentane
2,3-dimethylbutane 2,2-dimethylbutane
The Same
These are the five isomers of hexane, C6H14
Methane becomes Methyl
Ethane becomes Ethyl
Propane becomes Propyl
C H
H
HHC
H
HH
C H
CH3
HHC
CH3
HH
C H
CH3CH2
HHC
CH3CH2
HH
1 Methane Methyl2 Ethane Ethyl3 Propane Propyl4 Butane Butyl5 Pentane Pentyl6 Hexane Hexyl7 Heptane Heptyl8 Octane Octyl9 Nonane Nonyl10 Decane Decyl
12
3
4
56
7
Find the longest chain 7 carbons. It’s a heptane
Number the atoms
Add the substituents inalphabetic order
4-ethyl-2-methylheptane
5 carbon chain. It’s a pentane
3 methyls so use the prefix - tri
2 di-3 tri-4 tetra-5 penta-6 hexa-
2,2,4-trimethylpentane
not
4,4,2-trimethylpentane
9 carbon chain
It’s a nonane
2 methyl groups and1 ethyl group
4-ethyl-3,7-dimethylnonane
not
6-ethyl-3,7-dimethylnonane
hexane2-methylpentane
3-methylpentane
2,3-dimethylbutane
2,2-dimethylbutane
What is special about this compound?
3-methylhexane
These two compounds are different.
CH3 H H CH3
One Is left handed and the other is right handed.
The two compounds are mirror images.
Put your thumb toward you representing the hydrogenatom, the lightest group. Point your fingers toward thepropyl group, the heaviest group. Curl your fingerstoward the ethyl group, the second heaviest group.
Left Handed or S Right Handed or R
These molecules are Chiral. They have handedness.
S-3-ethyl-2-methylhexane
H
Molecular Formulas for Alkanes
are all of the form CnH2n+2
2,2,4-trimethylpentanen-octane
n = 8 2n + 2 = 18 C8H18
Molecular Formulas for Alkenes
are all of the form CnH2n
2,4,4-trimethyl-2-pentene1-octene
n = 8 2n = 16 C8H16
H
H
H H
cis-2-pentenetrans-2-pentene
If an alkene has two identical substituents on the twodifferent carbons, they can be named cis or trans.
If the identical substituents are on the same side we call themolecule cis. If they are on opposite sides we call the molecule trans.
The two compounds shown above are stereoisomers.
If two substituents on one carbon are the samecis and trans do not apply
But what do we do if all groups are different?
Instead of cis or trans use E or Z
Z means the two heaviest groups are on thesame side of the double bond.
E means the two heaviest groups are on different sides of the double bond.
(E) - 3-methyl-3-heptene (Z) - 3-methyl-3-heptene
cis-3,5-dimethyl-2-hexene
(E)-2,4-dimethyl-3-hexene
2-ethyl-4-methyl-1-pentene
Molecular Formulas for Alkynes
are all of the form CnH2n-2
1-octyne
n = 8 2n - 2 = 14 C8H14
H
2-methyl-3-hexyne
3-ethyl-6-methyl-1-heptyne
trans-2-pentene cyclopentane
C5H10
Cycloalkanes CnH2n
cyclopropane cyclobutane
cyclopentane cyclohexane
60
Cyclopropane
CH3 H
CH3H
CH3 CH3
HH
cis-1,2-dimethylcyclopropane
trans-1,2-dimethylcyclopropane
trans-1,2-dimethycyclobutane
cis-1-ethyl-3-methylcyclobutane
120
Cyclohexane
Ideal angles are 120 degrees.
Actual angles are 109.5degrees, the tetrahedral angle
Benzene
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
1,3-dimethylbenzene
1,4-dimethylbenzene
1,2-dimethylbenzenemethylbenzene
toluene
ortho
meta para
Draw all compounds of formula C4H8
Draw all compounds of formula C4H6
Draw all compounds of formula C4H10