华中师范大学化学专业英语课件8

State Key Laboratory for Physical Chemistry of Solid Surfaces
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• However, this structure also failed to answer many questions about the properties of benzene. If the structure above were correct, benzene would still be expected to be highly reactive because of the three double bonds it contains.
that the substituents are on the positions with
compounds are known as aliphatic (脂肪族的）
compounds. • The term aliphatic comes from the Greek word
aleiphar, which means “oil”.
State Key Laboratory for Physical Chemistry of Solid Surfaces
form a continuous p bond about the benzene ring. • The p electrons are not localized between any two
carbon atoms. Rather, all six p electrons are
delocalized over the entire ring.
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
12.5 nomenclature of benzene
• The compounds that form when one or more H atoms
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
12.4 Structural Formulas for benzene
• The drawing we use to represent the structure of benzene is a hexagon with a circle inside it. The
厦门大学固体表面物理化学国家重点实验室
• In this chapter, we will introduce another class of organic compounds called the aromatics（芳香 族）.
• Benzene(苯) and its derivatives were originally called aromatic compounds because of their rather pleasant aromas.
• Open-chain structures, such as CH2=CH-C≡CCH=CH2, were first proposed, but it is inconsistent with the chemical property that benzene undergoes substitution with bromine, instead of the addition reaction with bromine(溴).
12.1 Introduction • So far most of the compounds we have studied have
been open-chain compounds. We also discussed a few ring compounds, the cycloalkanes and cycloalkenes, and found their properties to be very much like their counterparts, the alkanes and alkenes. • Open-chain compounds and their corresponding ring
• Furthermore, if the benzene ring really did have alternating single and double bonds, the distance between doubly bonded C atoms would be shorter than that between singly bonded C atoms, yet all physical measurements showed that the six C to C bond distances were identical.
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
H
H
H CC
H
C
CCCHຫໍສະໝຸດ HH HH
H
a)
H
H
b)
Benzene bonding: a) s framwork; b) continuous p bond.
benzene ring.
3 2I
I3 2
3
2
4
1 Cl 4
1 Cl I 4
1 Cl
5
6
5
6
5
6
1-chloro-2-iodobenzene 1-chloro-3-iodobenzene 1-chloro-4-iodobenzene
• Number the position of the benzene ring so
substituent, the compound is called chlorobenzene and
if the attached group is nitro(-NO2), the name of the
compound is nitrobenzene.
Cl
NO2
Chlorobenze ne Nitrobenze ne
• Each C atom has three sp2 hybrid orbitals, with
which the s framework of benzene bonding is
established. • Each C atom has one unhybridized p orbital
containing one electron. These overlapping p orbitals
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
• The chemist August Kekulé(1829-1896) proposed an alternative structure in which the six carbon atoms of benzene are joined together to form a hexagon with each ring C atom bonded to an H atom. • The inspiration for this idea supposedly sprang from a daydream in which Kekulévisualized “long rows …, all twining and twisting in snakelike motion,” and then saw that “One of the snakes had seized hold of its own tail…”. In any case, Kekulé‘s structure turned out to be correct. Benzene is a ring compound.
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
12.2 Ring Structure of Benzene
• In the 1820s, a pure liquid hydrocarbon called benzene was first isolated. Chemists found that the molecular formula of this new substance was C6H6, but it took some time for them to figure out a structure which was consistent with the properties of benzene.
Chemistry English
Lecture 8
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
Chapter 12 Benzene and The Aromatic Hydrocarbons
circle represents the continuous p bonding about
the benzene ring.
• Another commonly encountered depiction of benzene is the following: