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1、Chemistry English,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,Lecture 8,12.1 IntroductionSo 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 prope
2、rties to be very much like their counterparts, the alkanes and alkenes.Open-chain compounds and their corresponding ring compounds are known as aliphatic (脂肪族的）compounds.The term aliphatic comes from the Greek word aleiphar, which means “oil”.,Chapter 12 Benzene and The Aromatic Hydrocarbons,In this
3、 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. The term aromatic now refers to any compound which has a benzene ring in its structure or has ch
4、emical properties similar to those of benzene. In the sections that follow, we will describe the structure and the properties of benzene and many of its derivatives.,12.2 Ring Structure of Benzene,In the 1820s, a pure liquid hydrocarbon called benzene was first isolated. Chemists found that the mole
5、cular 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.Open-chain structures, such as CH2=CH-CC-CH=CH2, were first proposed, but it is inconsistent with the chemical property that benzene undergoes su
6、bstitution with bromine, instead of the addition reaction with bromine(溴).,The chemist August Kekul(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 supp
7、osedly sprang from a daydream in which Kekul visualized “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, Kekuls structure turned out to be correct. Benzene is a ring compound.,However, this structure also
8、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. Furthermore, if the benzene ring really did have alternating single and double bonds, the distanc
9、e 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.,12.3 Bonding in Benzene,There are three atoms attached to each C atom in benzene. Each C atom has three sp2 hybrid orbital
10、s, 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 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
11、 are delocalized over the entire ring.,Benzene bonding: a) s framwork; b) continuous p bond.,The drawing we use to represent the structure of benzene is a hexagon with a circle inside it. The circle represents the continuous p bonding about the benzene ring. Another commonly encountered depiction of
12、 benzene is the following:,12.4 Structural Formulas for benzene,12.5 nomenclature of benzene,The compounds that form when one or more H atoms of benzene are substituted with other atoms or groups of atoms are named as derivatives of benzene.In monosubstituted benzenes one H atom is replaced by anoth
13、er atom or group X. To name such compounds, the name of the substituent X is followed by the word benzene. For instance, if a chlorine atom is the substituent, the compound is called chlorobenzene and if the attached group is nitro(-NO2), the name of the compound is nitrobenzene.,Disubstituted benze
14、nes: There are three different ways to place two substituents on a benzene ring.Number the position of the benzene ring so that the substituents are on the positions with the lowest possible numbers. The number 1 is assigned to the substituent that is lower in alphabetical order.,12.6 Phenyl Group,S
15、ome benzene compounds are more convenient named by considering the benzene itself to be a substituent. The benzene substituent, which is named phenyl, is formed by removing one H atom from the benzene ring.,12.7 Chemical Properties of Benzene,Halogenation: Benzene reacts with bromine or chorine to f
16、orm bromobenzene or chlorobenzene in the present of an iron catalyst (Fe, Fe Br3 or FeCl3). Nitration: Nitrobenzene can be prepared by reacting with nitric acid in the presence of sulfuric acid.,12.8 Arenes(芳烃),Hydrocarbons such as alkylbenzenes toluene and ethylbenzene, which have both aliphatic an
17、d aromatic components, are called arenes.Because arenes have both aromatic and aliphatic character, they also have properties of aliphatic as well as of aromatic compounds.Benzene itself is more toxic than any of the arenes. The reason for this is related to the inertness of benzene, which makes it
18、difficult for the body to eliminate it.,12.9 Fused-RingAromatics,A fused-ring aromatic is a compound that forms when two or more aromatic rings are joined at two or more C atoms. The source of fused-ring aromatics is a substance called coal tar(焦油), the liquid residue produced when coal is heated in
19、 the absence of air.,Chapter 13 Alcohols and Ethers,13.1 IntroductionIn the next few chapters we will introduce the organic compounds which have oxygen atoms in their functional groups. Two of these are alcohols and ethers.We can produce the structures of both classes of compounds starting with a wa
20、ter molecule, HOH. By replacing one of the H atoms in water with a C atom, we have the general formula of an alcohol, written ROH, where R refers to a hydrocarbon group.,For instance, if the R is a methyl group, the alcohol formula is CH3OH (methanol), and when R is a phenyl group, the alcohol is ph
21、enol. To produce the ether structure, both H atoms of water are replaced with hydrocarbon groups. We write the general formula with an R and R (R prime), meaning that the attached hydrocarbon groups can be the same or different. General ether formula: R-O-R,13.2 Naming Alcohols,Alkyl alcohols can be
22、 named as alkanols, a name derived by dropping the e from alkane and adding ol. For instance, the name of the alcohol derived from the simplest alkane comes from changing the methane to methanol (CH3OH). Ethanol is a two-carbon alcohol: CH3CH2OH.To name any alcohol more complex than these, we must i
23、ndicate the location of the OH group as well as those of any other branch groups. To do this we follow the rules below.,Rule 1: Choose the longest C to C chain to which the OH group is attached. This gives the parent alcohol name.Rule 2: Number the C atoms so that the C atom bonded to the OH group h
24、as the lowest possible number.Rule 3: Form the name by placing the number of the C atom to which the OH is attached in front of the parent alcohol. Indicate any branched groups according to the rules of alkane nomenclature.,Example,The parent name of this alcohol must be hexanol.Numbering the C chai
25、n.This hexanol is a 2-hexanol.The full name of this hexanol is 5-methyl-2-hexanol.,13.3 Primary, Secondary and Tertiary Alcohols,Alkyl alcohols can be divided into one of the three classes( primary, secondary or tertiary), depending on the type of C atom to which their hydroxyl groups are attached.I
26、n primary alcohols the hydroxyl group is attached to a primary C atom, that is, a carbon atom that is bonded to only one other C atom, e.g., CH3CH2OH.,In secondary alcohols, the hydroxyl group is attached to a secondary C atom, that is, a carbon atom that is bonded to two other C atoms. The followin
27、g alcohols are thus secondary alcohols.In tertiary alcohols, the OH group is attached to a tertiary C atom, a C atom which forms bonds with three other C atoms.,13.4 Naming Ethers,Ethers are named by giving the names of R and R hydrocarbon groups in the general formula ROR, in alphabetical order, fo
28、llowed by the word ether.When R and R are the same, the name of the R groups is given only once or the prefix di- is used in the name.Using this method we can name the ethers below:CH3CH2OCH2CH3 (diethyl ether) CH3OCH2CH3(Ethyl methyl ether),See you next week!Have a nice day!,Assignment: Write an article (about 200 words) with the title Aromatics: Pleasant or dangerous?.,
