Topic : Alkanes
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Transcript of Topic : Alkanes
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Topic: AlkanesDo Now: Draw the possible bonds a single carbon atom can have if it has a bonding
capacity of 4
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Alkanes• Homologous series of saturated hydrocarbons• Release energy when burned• CnH2n+2 – all have this general formula
CH4 H
H–C–H H
C2H6 H H
H–C–C–H H H
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Saturated hydrocarbons: organic compounds containing only Single bonds – can’t add any more Hydrogens
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Properties of Alkanes• Low Reactivity
–Except readily undergo combustion (fuels)• Nonpolar – don’t dissolve well in water• Low melting & low boiling points
–both increase with molecular mass• High vapor pressures
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Properties of Alkanes
• Change systematically with # of C’s
• As # of C’s increases, boiling point increases– molecules get heavier so harder to change into gas
phase
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A. Low melting pointB. High melting pointC. Soluble in polar solventsD. Insoluble in nonpolar solvents
Which property is generally characteristic of an organic compound?
Correct response = A
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A. CH4
B. C2H6
C. C3H8
D. C4H10
Which of the following compounds has the highest boiling point?
Correct answer = D
nonpolar coval cmpd:
• bp depends on strength of van der Waals interactions
• van der Waals forces ↑ as size of molecule ↑
• bigger molecule = bigger electron cloud
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Alkanes (CnH2n+2)
C3H8
H H HH–C–C–C–H
H H H
CH3CH2CH3
Chemical Formula
Structural Formula
Condensed Structural Formula
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straight-chain alkane
C4H10
H H H HH–C–C–C–C–H
H H H H
Or CH3CH2CH2CH3
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Naming straight-chain Alkanes
• Name: describes molecule so can draw it
• all alkanes have the suffix –ane• prefix: tells # of C’s
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10Dec9Non8Oct7Hept6Hex5Pent4But3Prop2Eth1Meth
# of C atomsPrefix
C5H12
C4H10
C3H8
C2H6
Meth + aneCH4
NameFormula
Ethane
PropaneButanePentane
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Naming Branched-Chain Alkanes
• goal of name is to describe molecule so you can draw it
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Naming branched-chain alkanes1. Find longest continuous chain of C atoms
- Bends don’t matter!
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2. base name derived from # C’s in continuous chain
9 carbon chain = nonane
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3. Branches named first and in alphabetical order * to name branches, count # C atoms & add “yl” to prefix name* If more than one of same type of branch - use di, tri, etc.
ethyl
ethyl
ethylmethyl
propyl
triethyl, methyl, propyl
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Assign number to Branches based on longest carbon chain
* you want numbers to add up to the lowest #
ethyl
ethyl
ethyl
methyl
propyl
1
23456
789
4, 4, 5, 5, 6 = add up = 24
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Assign number to Branches based on longest carbon chain
* you want numbers to add up to the lowest #
ethyl
ethyl
ethyl
methyl
propyl
1234 5 6 7
8
9
4, 5, 5, 6, 6 = add up = 26
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4. Put it all together
ethyl
ethyl
ethyl
methyl
propyl
1
23456
789
3. 4, 4, 5, 5, 6
2. triethyl, methyl, propyl
1. nonane
nonane4,4,6-triethyl 5-methyl 5-propyl
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HH–C–H
H HH–C–C–C–H
H H H
2-methyl propaneNo because if methyl was anywhere else it wouldn’t be propane
Longest continuous chain has 3 carbon atoms – propane
1 2 3
Methyl propane
C4H10
CH3CH(CH3)CH3
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HH–C–H
H–C–H H H HH–C–C–C–C–H H H H H–C–H H 1
4 3
6
5
2
Longest continuous chain has 5 C atoms: pentane
Branch: 1 carbon = methylBranch: 12 carbon = ethyl
Branch located at C-2 and 3
3-ethly 2-methyl pentane
C8H18
CH3CH(CH3) CH(CH2CH3)CH2CH3
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Branched-chain alkanes
Beginning with butane, C4H10, there is more than 1 way to arrange the atoms
HH–C–HH H
H–C–C–C–HH H H
ISOMERS