topic : alkanes
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Topic : Alkanes. Do Now: Draw the possible bonds a single carbon atom can have if it has a bonding capacity of 4. Alkanes. Homologous series of saturated hydrocarbons Release energy when burned C n H 2n+ 2 – all have this general formula CH 4 H - PowerPoint PPT PresentationTRANSCRIPT
Topic: AlkanesDo Now: Draw the possible bonds a single carbon atom can have if it has a bonding
capacity of 4
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
Saturated hydrocarbons: organic compounds containing only Single bonds – can’t add any more Hydrogens
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
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
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
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
Alkanes (CnH2n+2)
C3H8
H H HH–C–C–C–H
H H H
CH3CH2CH3
Chemical Formula
Structural Formula
Condensed Structural Formula
straight-chain alkane
C4H10
H H H HH–C–C–C–C–H
H H H H
Or CH3CH2CH2CH3
Naming straight-chain Alkanes
• Name: describes molecule so can draw it
• all alkanes have the suffix –ane• prefix: tells # of C’s
10Dec9Non8Oct7Hept6Hex5Pent4But3Prop2Eth1Meth
# of C atomsPrefix
C5H12
C4H10
C3H8
C2H6
Meth + aneCH4
NameFormula
Ethane
PropaneButanePentane
Naming Branched-Chain Alkanes
• goal of name is to describe molecule so you can draw it
Naming branched-chain alkanes1. Find longest continuous chain of C atoms
- Bends don’t matter!
2. base name derived from # C’s in continuous chain
9 carbon chain = nonane
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
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
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
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
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
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
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