ORGANIC CHEMISTRY
Chapter 1
1.12 The Structure of Methane
and Ethane: sp3 Hybridization
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Chapter 1
1.12A The Structure of Methane
sp3 Hybridization
The 4 sp3 orbitals should be oriented at angles
of 109.5° with respect to each other.
An sp3-Hybridized carbon gives a tetrahedral
structure for methane, and with four equivalent
C—H bonds.
H
H
H
C
H
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ORGANIC CHEMISTRY
Chapter 1
1.12B The Structure of Ethane
sp3-Hybridized carbon atoms
1 carbon-carbon σ-bond and 6 carbon-hydrogen σbonds.
Because a σ-bond has cylindrical symmetry along the
bond axis, rotation of groups joined by a single bond
does not usually require a large amount of energy (1326 kJ/mol). Consequently, groups joined by single
bonds rotate relatively freely with respect to one
another.
H
H
H
H
C
C
H
H
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Chapter 1
1.13 The Structure of Ethene
(Ethylene): sp2 Hybridization
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Chapter 1
sp2-Hybridized carbon atoms.
The three sp2 orbitals that result from
hybridization are directed toward the corners of
a regular triangle (with angles of 120° between
them). The p orbital that is not hybridized is
perpendicular to the triangle formed by the
hybrid sp2 orbitals.
5 σ-bonds(1 C—C, 4 C—H) and 1 π-bond.
Hydrocarbons whose molecules contain a
carbon-carbon double bond are called alkenes.
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ORGANIC CHEMISTRY
Chapter 1
H
H
C
H
118°
C
121°
H
H
H
H
C
C
H
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 1
1.13A Restricted Rotation and the
Double Bond
There is a large energy barrier to rotation (about
264 kJ/mol) around the double bond.
The rotational barrier of a carbon-carbon single
bond is 13-26 kJ/mol
Rotation of the p orbitals 90o totally breaks the
π bond
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Chapter 1
1.13B Cis-Trans Isomerism
CH3
CH3
C
H
CH3
H
C
C
H
CH3
C
H
cis-2-Butene
trans-2-Butene
顺-2-丁烯
反-2-丁烯
The compound with substituents on the same side of
the double bond is referred to as cis-isomer; the isomer
with substituents on opposite side is trans.
The two compounds differ only in the arrangement of
their atoms in space. Isomer of this kind are classified
formally as stereoisomers （立体异构体）.
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Chapter 1
1.14 The Structure of Ethyne
(Acetylene): sp Hybridization
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Chapter 1
Hydrocarbons that contain a carbon-carbon
triple bond are called alkynes.
The arrangement of atoms around each carbon
is linear with bond angles 180o
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 1
The carbon in ethyne is sp hybridized.
The two sp orbitals are oriented 180o relative to each
other around the carbon nucleus.
The carbon-carbon triple bond consists of two π bonds
and one σ bond.
Department of Chemistry, Xiamen University
ORGANIC CHEMISTRY
Chapter 1
Depictions of ethyne show that the electron density
around the carbon-carbon bond has circular symmetry
H C
C H
H
C
C
H
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ORGANIC CHEMISTRY
Chapter 1
Bond Lengths of Ethyne, Ethene, and
Ethane
Compounds
Carbon-carbon
bond lengths (Å)
Carbon-hydrogen
bond lengths (Å)
Ethyne
1.20
1.06
Ethene
1.34
1.09
Ethane
1.54
1.10
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Chapter 1
The carbon-carbon bond length is shorter as more
bonds hold the carbons together.
The carbon-hydrogen bond lengths also get shorter
with more s character of the bond.
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Chapter 1
1.15 A Summary of Important
Concepts That Come From
Quantum Mechanics
1.16 Molecular Geometry: The
Valence Shell Electron-pair
Repulsion (VSEPR) Model
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Chapter 1
1.17 Representation of
Structural Formulas
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Chapter 1
1.17A Dash Structural Formulas
H
H
H
H
H
C
C
C
C
H C
H
H
H
H
H
H
Dash formula 蛛网式
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Chapter 1
1.17B Condensed Structural Formulas
CH3
CH
CH3
CH2
CH3
CH3CHCH2CH3
CH3
Condensed Structural Formulas（结构简式）
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Chapter 1
1.17C Cyclic Molecules
H
H
CH2
C
H
H
C
H
C
CH2
CH2
H
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Chapter 1
1.17D Bond-Line Formulas
OH
Bond-Line Formulas（键线式）
Bond-line formulas are often used for cyclic compounds:
CH2
CH2
CH2
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Chapter 1
1.17E Three-Dimensional Formulas
H
H
H
C
H
Wedge-dashed wedge-line formula
虚线－楔线式
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