Hydrocarbons

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Hydrocarbons
Hydrides of Carbon
CxHy
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Carbon has four valence electrons. Wants to
form four bonds.
Methane
Hydrogen has one valence electron and wants to
form one bond
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Butane
Propane
Ethane
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Methane CH4
Ethane C2H6
Propane C3H8
Butane C4H10
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Ethane Conformations
Eclipsed
Staggered
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Variation of Energy with Rotation of C-C bond in
Ethane
12 kJ
0 60 120 180 240
300 360
Angle of Rotation, degrees
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2-methylpropane or isobutane
Butane C4H10
n-
These two molecules are structural isomers. They
differ in the way their atoms are connected They
have different chemical and physical properties.
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2-methylpropane or isobutane
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n-hexane
These structures represent different conformations
of n-hexane, not isomers.
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n-hexane
2-methylpentane
3-methylpentane
4-methylpentane
2,3-dimethylbutane
2,2-dimethylbutane
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These are the five isomers of hexane, C6H14
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Methane becomes
Methyl Ethane becomes
Ethyl Propane becomes
Propyl
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1 Methane Methyl 2 Ethane Ethyl 3 Propane Propyl
4 Butane Butyl 5 Pentane Pentyl 6 Hexane Hexyl
7 Heptane Heptyl 8 Octane Octyl 9 Nonane Nonyl
10 Decane Decyl
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Find the longest chain
7 carbons. Its a heptane
Add the substituents in alphabetic order
4-ethyl-2-methylheptane
Number the atoms
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5 carbon chain. Its 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
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9 carbon chain Its a nonane
2 methyl groups and 1 ethyl group
4-ethyl-3,7-dimethylnonane
not 6-ethyl-3,7-dimethylnona
ne
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hexane
2-methylpentane
2,3-dimethylbutane
3-methylpentane
2,2-dimethylbutane
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What is special about this compound?
3-methylhexane
These two compounds are different.
The two compounds are mirror images.
One Is left handed and the other is right handed.
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These molecules are Chiral. They have handedness.
Right Handed or R
Left Handed or S
Put your thumb toward you representing the
hydrogen atom, the lightest group. Point your
fingers toward the propyl group, the heaviest
group. Curl your fingers toward the ethyl group,
the second heaviest group.
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S-3-ethyl-2-methylhexane
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Molecular Formulas for Alkanes are all of the
form CnH2n2
2,2,4-trimethylpentane
n-octane
C8H18
n 8 2n 2 18
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Molecular Formulas for Alkenes are all of the
form CnH2n
2,4,4-trimethyl-2-pentene
1-octene
C8H16
n 8 2n 16
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cis-2-pentene
trans-2-pentene
If an alkene has two identical substituents on
the two different 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.
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If two substituents on one carbon are the
same cis and trans do not apply
But what do we do if all groups are different?
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(E) - 3-methyl-3-heptene
(Z) - 3-methyl-3-heptene
Instead of cis or trans use E or Z
Z means the two heaviest groups are on the same
side of the double bond. E means the two
heaviest groups are on different sides of the
double bond.
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cis-3,5-dimethyl-2-hexene
(E)-2,4-dimethyl-3-hexene
2-ethyl-4-methyl-1-pentene
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Molecular Formulas for Alkynes are all of the
form CnH2n-2
1-octyne
C8H14
n 8 2n - 2 14
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2-methyl-3-hexyne
3-ethyl-6-methyl-1-heptyne
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C5H10
trans-2-pentene
cyclopentane
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Cycloalkanes CnH2n
cyclopropane
cyclobutane
cyclopentane
cyclohexane
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Cyclopropane
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trans-1,2-dimethylcyclopropane
cis-1,2-dimethylcyclopropane
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trans-1,2-dimethycyclobutane
cis-1-ethyl-3-methylcyclobutane
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Cyclohexane
Ideal angles are 120 degrees.
Actual angles are 109.5 degrees, the tetrahedral
angle
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Benzene
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toluene
ortho
1,2-dimethylbenzene
methylbenzene
meta
para
1,4-dimethylbenzene
1,3-dimethylbenzene
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Draw all compounds of formula C4H10
Draw all compounds of formula C4H8
Draw all compounds of formula C4H6