Chapter 2 Alkanes and Cycloalkanes

1 2 3 4 5 6
4-Ethyl-2,2-dimethylhexane (not 2,2-dimethyl-4-ethylhexane)
2-14
Problem
Explain why each is an incorrect IUPAC name, and write the correct IUPAC name. (a) 1,3-dimethylbutane (b) 4-methylpentane (c) 2,2-dimethylbutane (d) 2-ethyl-3-methylpentane (e) 2-propylpentane (f) 2,2-diethylheptane (g) 2,2-dimethylcyclopropane (h) 1-ethyl-5-methylcyclohexane
CH3 CH 3 CHCH3
1 2 3
2-Methylprop ane
4. If there is one substituent, number the chain from the end that gives it the lower number.
CH3 CH3 CH2 CH2 CHCH3
5 4 32 2 1 1 34 5
Alk ane CH4 CH3 CH3 Name Methane Ethane Alk yl group CH3 CH3 CH2 Name Methyl group Ethyl group
2-10
Nomenclature - IUPAC
1.The name of a saturated hydrocarbon with an unbranched chain consists of a prefix and suffix. 2. The parent chain is the longest chain of carbon atoms. 3. Each substituent is given a name and a number. Use a hyphen to connect the number to the name.
Alkynes (Chapter 7) One or more carbon-carbon trip le bonds
Arenes (Chapter 21-22) One or more benz enelike rings
HH H-C-C-H H H
Ethane
H H C C H H
Ethene (Ethylene)
CH3 5 CH3 4 CH3 CHCH2 CH 1 2 3 CH3
2 4
and
5
1
3
CH3 CH3 CH2 CHCHCH3 2 1 CH3
5 4 3
5
4
3
2
1
2-7
Constitutional Isomerism
The
ability of carbon to form strong bonds with other carbon atoms results in a staggering number of constitutional isomers.
formulas:
• an abbreviated way to draw structural formulas. • each vertex and line ending represents a carbon.
Ball-and stick mod el Line-an gle formula Structu ral formu la CH3 CH2 CH3 Propane CH 3 CH2 CH2 CH3 Butan e CH 3 CH 2 CH 2 CH 2 CH 3 Pentan e
6 5 4 3 2 1 1 2 3 4 5 6
2,4-Dimethylhexane
(not 3,5-dimethylhexane)
2-12
Nomenclature - I UPAC
6. If there are two or more different substituents, • list them in alphabetical order. • number from the end of the chain that gives the substituent encountered first the lower number.
CH3 CH3 CH3 CH3 CHCH2 CH and CH3 CH2 CHCHCH3 CH3 CH3 (each is C7 H 16)
• Write the molecular formula of each. • Find the longest carbon chain. • Number each chain from the end nearest the first branch. • Compare chain lengths as well as the identity and location of branches. They are constitutional isomers.
Molecular Formula CH 4 C5 H1 2 C1 0 H2 2 C1 5 H3 2 C2 5 H5 2 C3 0 H6 2 Constitutional Isomers 1 3 75 4,347 36,797,588 4,111,846,763
World population is about 6,000,000,000
2-16
Nomenclature - Common
The
number of carbons in the alkane determines the name.
• All alkanes with four carbons are butanes, those with five carbons are pentanes, etc. • iso- indicates the chain terminates in -CH(CH3)2; neothat it terminates in -C(CH3)3.
CH3 CH 2 CH 2 CH 3 Butane (bp -0.5° C)
CH3 CH3 CHCH 3 2-Methylpropane (bp -11.6° C)
2-6
Constitutional Isomerism
• Question: Do these formulas represent constitutional isomers?
Alkanes and Cycloalkanes
Chapter 2
2-1
Structure
Hydrocarbon:
A compound composed only of carbon and hydrogen. Saturated hydrocarbon: A hydrocarbon containing only single bonds. Alkane: A saturated hydrocarbon whose carbons are arranged in an open chain. Aliphatic hydrocarbon: Another name for an alkane.
2-8
Nomenclature - IUPAC
Suffix
-ane specifies an alkane, e.g. ethane. Prefix tells the number of carbon atoms.
Number of Prefix carbons meth1 eth2 prop3 but4 pent5 hex6 7 heptoct8 non9 dec10 Number of Prefix carbons undec11 dodec12 tridec13 tetradec14 pentadec15 hexadec16 heptadec17 octadec18 nonadec19 eicos20
2-9
Nomenclature - IUPAC
Parent
name: The longest carbon chain. Substituent: A group bonded to the parent chain.
• Alkyl group: A substituent derived by removal of a hydrogen from an alkane; given the symbol R-.
H-C C-H
Ethyne (Acety lene Benzene
2-3
Structure
Shape
Fra Baidu bibliotek
• tetrahedral about carbon • all bond angles are approximately 109.5°
109.5
2-4
Drawing Alkanes
Line-angle
1 2 3 4 5 6 7 7 6 5 4 3 2 1
3-Ethyl-5-methylheptane
(not 3-methyl-5-ethylheptane)
2-13
Nomenclature - IUPAC
7. The prefixes di-, tri-, tetra-, etc. are not included in alphabetization. • Alphabetize the names of substituents first and then insert these prefixes.
2-5
Constitutional Isomerism
Constitutional
isomers: Compounds with the same molecular formula but a different connectivity of their atoms.
• example: C4H10
2-Methylpentane
(not 4-methylpentane)
2-11
Nomenclature - IUPAC
5. If there are two or more identical substituents, number the chain from the end that gives the lower number to the substituent encountered first. • Indicate the number of times the substituent appears by a prefix di-, tri-, tetra-, etc. • Use commas to separate position numbers.
2-15
Nomenclature - IUPAC
Alkyl
Name methyl ethyl propyl 1-methylethyl (is opropyl)
groups
Condens ed Structural Formula - CH 3 - CH 2 CH 3 - CH 2 CH 2 CH 3 - CH CH 3 CH3 1,1-dimethylethyl (tert- butyl) Name butyl 2-methylpropyl (is obutyl) 1-methylpropyl (sec-butyl) Condens ed Structural Formula - CH 2 CH2 CH 2 CH 3 - CH 2 CHCH 3 CH3 - CH CH 2 CH 3 CH3 CH 3 - CCH3 CH 3
2-2
Hydrocarbons
Hy drocarbons Saturated Unsaturated
Class Carboncarbon bonding Examp le Name
Alkanes (Chapter 2) Only carboncarbon single bonds
Alkenes (Chapters 5-6) One or more carbon-carbon double bonds