Chapter 4 Alkanes 1.For alkanes beyond butane, add -ane to the Greek root for the number of carbons....
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Transcript of Chapter 4 Alkanes 1.For alkanes beyond butane, add -ane to the Greek root for the number of carbons....
Chapter 4 Alkanes
• 1. For alkanes beyond butane, add -ane to the Greek root for the number of carbons.
• C-C-C-C-C-C = hexane• 2. Alkyl substituents: drop the -ane and
add -yl.
• -C2H5 is ethyl
Rules for Naming Alkanes
● identify the longest chain of carbon atoms. In the exampl e shown (Fig. 2a) , the longest chain consists of five carbon atoms and a pentane chain;● number the longest chain of carbons, starting from the end nearest the branch point (Fig. 2b);● identify the carbon with the branching group (number 2 in Fig. 2b);● identify and name the branching group. CH3 is called methyl and not methane.● name the structure by first identifying the substituent and its position in the chain, then naming the longest chain. 2-methylpentane
Pentanes
CH
H
C
H
H
C
H
H
C
H
C
HH
H
H
H
n-pentane, C5H12
CHH
C CHH
C H
H
H
HH
CH
HH
isopentane, C5H12
=>
C
CH3
CH3H3C
CH3
neopentane, C5H12
构造异构体
IUPAC Names• Find the longest continuous carbon chain.• Number the carbons, starting closest to the
first branch.• Name the groups attached to the chain, using
the carbon number as the locator.• Alphabetize substituents.• Use di-, tri-, etc., for multiples of same
substituent.
Longest Chain• The number of carbons in the longest chain
determines the base name: ethane, hexane. If there are two possible chains with the same number of carbons, use the chain with the most substituents.
C
CH3
CH2
CH3
CH CH2 CH2 CH3
CH CH2 CH3H3C
H3C
=>
Number the Carbons
• Start at the end closest to the first attached group.
• If two substituents are equidistant, look for the next closest group.
1
2
3 4 5
6 7CHH3C
CH3
CH
CH2CH3
CH2 CH2 CH
CH3
CH3
=>
Name Alkyl Groups
• CH3-, methyl
• CH3CH2-, ethyl
• CH3CH2CH2-, n-propyl
• CH3CH2CH2CH2-, n-butyl
CH3 CH CH2 CH3
sec-butyl
CH3 CH
CH3
CH2
isobutyl
CH3 CH CH3
isopropyl
CH3C
CH3
CH3
tert-butyl
=>
Propyl Groups
C
H
H
H
C
H
H
C
H
H
H
n-propyl
C
H
H
H
C
H
C
H
H
H
isopropyl
H
A primary carbon A secondary carbon
=>
Butyl Groups
C
H
H
H
C
H
C
H
H
C
H
H
H
C
H
H
H
C
H
C
H
HH
C
H
H
n-butyl sec-butyl
H
H
A primary carbon A secondary carbon
=>
Isobutyl Groups
CH
H
H
C
CH H
C
HH
H H
CH
H
H
C
CH H
C H
HH
H
H
H
A primary carbon A tertiary carbon
=>
isobutyl tert-butyl
Alphabetize
• Alphabetize substituents by name.• Ignore di-, tri-, etc. for alphabetizing.
CHH3C
CH3
CH
CH2CH3
CH2 CH2 CH
CH3
CH3
3-ethyl-2,6-dimethylheptane =>
Higher Alkanes
• Anti conformation is lowest in energy.• “Straight chain” actually is zigzag.
CH3CH2CH2CH2CH3
CH C
CC
CH H H H
H H
H H
HH H =>
Constitutional isomers (构造异构体) are compounds which have the same molecular formula but have the atoms joined together in a different way. Constitutional isomers have different physical and chemical properties.
Physical Properties
• Solubility: hydrophobic• Density: less than 1 g/mL• Boiling points increase with increasing
carbons (little less for branched chains).
Melting points increase with increasing carbons (less for odd- number of carbons).
•
Hydrocarbons
mp -135oCbp-5oC
mp -145oCbp-10oC
mp -130oCbp+30oC
mp -160oCbp+28oC
mp -20oCbp+9oC
丁烷异构体
戊烷异构体
Branched Alkanes
• Lower b.p. with increased branching• Higher m.p. with increased branching• Examples:
H
CH3CH
CH3
CH2 CH2 CH3
bp 60°Cmp -154°C
CH3CH
CH3
CHCH3
CH3 bp 58°Cmp -135°C
=>
bp 50°Cmp -98°C
CH3 C
C 3
CH3
CH2 CH3
Major Uses of Alkanes
• C1-C2: gases (natural gas)
• C3-C4: liquified petroleum (LPG)
• C5-C8: gasoline
• C9-C16: diesel, kerosene, jet fuel
• C17-up: lubricating oils, heating oil
• Origin: petroleum refining =>
Conformational Analysis• Torsional strain: resistance to rotation.• For ethane, only 3.0 kcal/mol
=>
Cyclic Alkanes
•Carbon atoms can form rings containing only carbon-carbon single bonds.
•C3H6, C4H8, C6H12
Reactions of Alkanes
• Combustion
CH3CH2CH2CH3 + O2 CO2 + H2Oheat
8 10132
long-chain alkanes catalyst
shorter-chain alkanes
CH4 + Cl2 CH3Cl + CH2Cl2 CHCl3 CCl4+ +heat or light
=>
• Cracking and hydrocracking (industrial)
• Halogenation
Petroleum is a complex mixture of alkanes and cycloalkanes that can be separated by distillation
柴油
油脂沥青
C
H
H
H
H Cl+ C
H
H
H
+ H Cl
C
H
H
H
+ Cl Cl C
H
H
H
Cl + Cl
C
H
H
H
H + Cl Cl C
H
H
H
Cl + H Cl
Cl Cl + photon (h) Cl + Cl
自由基反应机理
Initiation链引发
Propagation(链增长)
Termination (链终止)CH3. + CH3
. CH3CH3