Organic Chemistry 2302271
รศ. ดร. ศุภศร วนิชเวชารุงเรือง
ภาควิชาเคมี คณะวิทยาศาสตร จุฬาลงกรณมหาวิทยาลัย
Assoc.Prof. Dr. S. Wanichwecharungruang
Department of Chemistry, Faculty of Science,
Chulalongkorn University
Glucose
Vanillin
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formaldehyde
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Functional groups
N
C
alkyl halide
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The general formula for an alkane is CnH2n+2 where n is the number
of carbon atoms in the molecule.
# Carbon
Name
Molecular
Formula
Structural
Formula
1
Methane
CH4
CH4
2
Ethane
C2H6
CH3CH3
3
Propane
C3H8
CH3CH2CH3
4
Butane
C4H10
CH3CH2CH2CH3
5
Pentane
C5H12
CH3CH2CH2CH2CH3
6
Hexane
C6H14
CH3(CH2)4CH3
7
Heptane
C7H16
CH3(CH2)5CH3
8
Octane
C8H18
CH3(CH2)6CH3
9
Nonane
C9H20
CH3(CH2)7CH3
10
Decane
C10H22
CH3(CH2)8CH3
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Conclusion? Why?
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Constitutional Isomer
Conclusion? Reasons?
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Compounds
Boiling point (oC)
2,2-dimethylpropane
10
pentane
36
2-methylbutane
28
Octane
125
2-methylheptane
118
2,2,3,3-tetramethylbutane
107
Conclusion?? Intermolecular forces involve include dipole-dipole,
dipole-induced dipole and induced dipole-induced dipole forces.
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IUPAC Names of Alkanes
Latin or Greek prefix for number of carbons + ane suffix
1 methane
CH4
2 ethane
CH3CH3
3 propane
CH3CH2CH3
4 butane
CH3CH2CH2CH3
5 pentane
CH3(CH2)3CH3
6 hexane
CH3(CH2)4CH3
7 heptane
CH3(CH2)5CH3
8 octane
CH3(CH2)6CH3
9 nonane
CH3(CH2)7CH3
10 decane
CH3(CH2)8CH3
11 undecane
CH3(CH2)9CH3
12 dodecane
CH3(CH2)10CH3
13 tridecane
CH3(CH2)11CH3
14 tetradecane
CH3(CH2)12CH3
15 pentadecane CH3(CH2)7CH3
16 hexadecane
17 heptadecane CH3(CH2)15CH3
18 octadecane
CH3(CH2)16CH3
19 nonadecane
CH3(CH2)17CH3
20 icosane
CH3(CH2)18CH3
25 pentacosane CH3(CH2)22CH3
30 triacontane
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CH3(CH2)8CH3
CH3(CH2)28CH3
Alkyl Groups
R-
take the IUPAC name of the corresponding unbranched alkane and
replace the -ane ending by -yl
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IUPAC Names of Branched Alkanes
1) Find the longest continuous carbon chain and use the IUPAC name of the
unbranched alkane as the basis.
2) Add name of substituent as a prefix.
3) Number the chain from the end nearest the substituent, and identify the
carbon to which the substituent is attached by number.
2,3-dimethylbutane
2,2-dimethylbutane
1-methylpentane
3-methylpentane
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Naming Alkyl Groups
•Identify longest continuous chain starting at point of attachment.
•Drop -ane ending from name of unbranched alkane having same number
of carbons as longest continuous chain and replace by -yl.
•Identify substituents on longest continuous chain.
•Chain is always numbered starting at point of attachment.
CH3CHCH3
CH3CH2CH2CHCH2CH2CH2CH2CH3
propyl
4-(1-methylethyl)-nonane
CH3CH2CHCH2CH2CH3
1-methylethyl
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CH3CHCH2CH3
4-ethyl-3-methylheptane
propyl, n-propyl (common name)
Primary alkyl group
1-methylethyl, isopropyl (common name)
Secondary alkyl group
2-methylpropyl, isobutyl (common name)
Primary alkyl group
1,1-dimethylethyl, tert-butyl (common name)
Tertiary alkyl group
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List substituents in alphabetical order
4-Ethyl-3,5-dimethyloctane
List substituents in alphabetical order
But don't alphabetize di-, tri-, tetra-, etc
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Primary, secondary, tertiary and quaternary carbons
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Cycloalkane
Cycloalkanes are alkanes that contain a ring of three or more carbons.
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Conformations of Alkanes and Cycloalkanes
Conformations are different spatial arrangements of a molecule
that are generated by rotation about single bonds.
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The terms anti and gauche apply only to bonds (or groups) on
adjacent carbons, and only to staggered conformations.
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gauche
The terms anti and gauche apply only to bonds (or groups)
on adjacent carbons, and only to staggered conformations.
Comparing between anti and guache, which one is more stable?
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torsional strain
repulsions between electrons in the C-H bonds on adjacent carbons
found only in eclipsed conformations
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torsional strain
(eclipsed bonds)
and
van der Waals
strain
van der Waals strain
(also called steric strain)
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The most stable conformation of unbranched alkanes
has (anti or guache) between adjacent carbons.
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Cycloalkanes
angle = 180(n -2)/n,
where n is the number of sides to the polygon
The natural angle for tetrahedral carbon is 109 o. According to Baeyer,
distortion of bond angles from 109.5° should give angle strain to
cycloalkanes with rings either smaller or larger than cyclopentane.
However, most ring pucker.
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torsional strain
angle strain
Less torsional strain
angle strain
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Stereoisomer
cis-1,2-Dimethylcyclopropane
Stereoisomer:
Stability?
trans-1,2-Dimethylcyclopropane
differ in spatial arrangement of atoms.
van der Waals strain makes cis stereoisomer less stable than trans
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chair conformation
axial vs equatorial
boat conformation
close contact between flagpole hydrogens -- van der Waals strain in boat
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eclipsed ---torsional strain
Skew boat --less van der Waals strain and less torsional strain
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chair-chair interconversion (ring-flipping):
- rapid process (activation energy = 45 kJ/mol)
- all axial bonds become equatorial and vice versa
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Conclusion
IUPAC Nomenclature of alkane and cycloalkane
Relationship between boiling point of alkanes and their structures
Constitutional isomer
Conformations of Alkanes and Cycloalkanes
Staggered, eclipsed and gauche structures
Boat, skew boat and chair conformations of cyclohexane
Axial vs equatorial bonds in cycloalkane
Torsional strain, van der Waals strain (steric strain), angle strain, ring strain
Stereoisomer, cis, trans
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