附件2 粒大浮 教 案 2003~~2004学年第Ⅰ学期 院(系、所、部)化学与环境学院有机化学研究所 教研室有机化学 课程名称有机化学(双语教学 授课对象化学教育 授课教师杨定乔 职称职务教授 教材名称 Organic Chemistry 2003年09月01日
附件 2 教 案 2003~~ 2004 学年 第 I 学期 院（系、所、部）化学与环境学院有机化学研究所 教 研 室 有机化学 课 程 名 称 有机化学(双语教学) 授 课 对 象 化学教育 授 课 教 师 杨定乔 职 称 职 务 教授 教 材 名 称 Organic Chemistry 2003 年 09 月 01 日
有机化学(双语教学)课程教案 授课题目(教学章节或主题):第二章.烷烃授课类型理论课 Alkanes 授课时间第2周第3-6节 教学目标或要求:了解基烷烃的结构理论以及自由基反应机理。 教学内容(包括基本内容、重点、难点) Valence Hybridization The number of atoms which are typically bonded to a given atom is termed the valence of that atom. Thus, in the examples shown below, hydrogen would have a valence of one, oxygen would have a valence of two, nitrogen and boron would have a valence of three, and carbon would have a valence of four H-O-H H-N-H H-B-H H-C-F As shown above, chemical analysis of simple hydrocarbons clearly demonstrates that carbon has a valence of four, that is, carbon forms four bonds and the simplest hydrocarbon (methane) has a molecular formula of CH. The arrangement of these atoms in space, however, is not immediately apparent, and at least three possibilities should be considered square planar, in which the four hydrogens occupy the comers of a square, centered about the carbon pyramidal, in which the carbon and three hydrogens occupy a plane with carbon in the middle and
有机化学(双语教学) 课程教案 授 课 题 目（ 教 学 章节 或 主题 ）：第 二 章 ．烷 烃 （Alkyanes） 授课类型 理论课 授课时间 第 2 周第 3-6 节 教学目标或要求：了解基烷烃的结构理论以及自由基反应机理。 教学内容（包括基本内容、重点、难点）： Valence & Hybridization The number of atoms which are typically bonded to a given atom is termed the valence of that atom. Thus, in the examples shown below, hydrogen would have a valence of one, oxygen would have a valence of two, nitrogen and boron would have a valence of three, and carbon would have a valence of four. As shown above, chemical analysis of simple hydrocarbons clearly demonstrates that carbon has a valence of four; that is, carbon forms four bonds and the simplest hydrocarbon (methane) has a molecular formula of CH4. The arrangement of these atoms in space, however, is not immediately apparent, and at least three possibilities should be considered: • square planar, in which the four hydrogens occupy the corners of a square, centered about the carbon. • pyramidal, in which the carbon and three hydrogens occupy a plane with carbon in the middle and
hydrogens at the vertices of a triangle, and tetrahedral, in which the carbon is in the center of a regular tetrahedron and hydrogens are at each vertex The orbital description of carbon, being ls 2s 2p, would suggest that, in order to form four bonds, a 2s electron must be promoted to the empty p-orbital to provide an electronic structure as shown below Recalling the geometry of the three p-orbitals, the pyramidal geometry might seem to be favored, since the three p-orbitals would form bonds at 90 angles with the s-orbital on the opposite face. This can easily be shown to be incorrect, however, by simply examining the number of molecules having the molecular formula CHCl, As shown below, if carbon was square-planar, there should be two forms of the molecule CH,Cl,(molecules having the same molecular formula, but different structures are termed isomers), one in which the two chlorines are on the same face of the square, and one in whi they are in opposite corners. If carbon was pyramidal, again two isomers would be predicted, one in which both chlorines are in the trigonal plane (with an angle of 120 ) and one in which one chlorine is in the apical position, with an angle of For a tetrahedron, however, since all bond angles are equal at 109.5,both chlorines would always occupy one ad jacent face of the tetrahedron (no matter which face you choose, as shown below) and only one isomer would be predicted
hydrogens at the vertices of a triangle, and, • tetrahedral, in which the carbon is in the center of a regular tetrahedron and hydrogens are at each vertex. The orbital description of carbon, being 1s2 2s2 2p2 , would suggest that, in order to form four bonds, a 2s electron must be promoted to the empty p-orbital to provide an electronic structure as shown below: 2s 2px 2py 2pz Recalling the geometry of the three p-orbitals, the pyramidal geometry might seem to be favored, since the three p-orbitals would form bonds at 90 angles, with the s-orbital on the opposite face. This can easily be shown to be incorrect, however, by simply examining the number of molecules having the molecular formula CH2Cl2. As shown below, if carbon was square-planar, there should be two forms of the molecule CH2Cl2 (molecules having the same molecular formula, but different structures are termed isomers), one in which the two chlorines are on the same face of the square, and one in which they are in opposite corners. If carbon was pyramidal, again two isomers would be predicted, one in which both chlorines are in the trigonal plane (with an angle of 120 ) and one in which one chlorine is in the apical position, with an angle of 90 . For a tetrahedron, however, since all bond angles are equal at 109.5 , both chlorines would always occupy one adjacent face of the tetrahedron (no matter which face you choose, as shown below) and only one isomer would be predicted
In fact, there is only one isomer with the molecular formula CH,Clz, and carbon has been confirmed to be tetrahedral, using modern x-ray diffraction me thods The observed tetrahedral geometry, however, does not agree with the prediction based on the orbital description, which would seem to predict a pyramidal structure. The explanation which is commonly given for this is that the four orbitals around carbon hybridize to form four equivalent orbitals having 75% p-character and 25% s-character. The resulting geometry is predicted to be tetrahedral and the driving force is electronic repulsion; placing the four orbitals in tetrahedral geometry provides the maximum separation between the electron pairs and minimizes electronic repulsion (the VESPER model cited in the previous section). a hybrid consisting of one s- and three p-orbitals is termed an sp hybrid(shown below) and an sp center should always be considered to approximate tetrahedral geometry, with the overriding factor being the driving force for the molecule to assume the lowest energy geometry, which is readily accessible. Hydrocarbons containing only sp carbons are called alkanes and represent the simplest and least reactive class of organic compounds. You should note that hybridization is a simple mathematical process which is useful in modifying electron densities, as predicted from the classical hydrogen atom analysis, to allow bonding geometries and electron densities in more complex molecules to be described. Again, the driving force for hybridization is the formation of a bonding geometry with the lowest net potential energy, which is accessible by energetically feasible mEANS. The tendency of molecules to seek to form the lowest energy structures(i the most stable reaction intermediate) is a commonly occurring theme in organic reactions and a knowledge of intermediate stability will often allow the direction of a reaction pathway to be accurately predicted Two additional orbital hybrids are also available for carbon; one in which the 2s-orbital combines with two of the available p-orbitals (sp ) and a second in
In fact, there is only one isomer with the molecular formula CH2Cl2, and carbon has been confirmed to be tetrahedral, using modern x-ray diffraction methods. The observed tetrahedral geometry, however, does not agree with the prediction based on the orbital description, which would seem to predict a pyramidal structure. The explanation which is commonly given for this is that the four orbitals around carbon hybridize to form four equivalent orbitals having 75% p-character and 25% s-character. The resulting geometry is predicted to be tetrahedral and the driving force is electronic repulsion; placing the four orbitals in tetrahedral geometry provides the maximum separation between the electron pairs and minimizes electronic repulsion (the VESPER model cited in the previous section). A hybrid consisting of one s- and three p-orbitals is termed an sp3 hybrid (shown below) and an sp3 center should always be considered to approximate tetrahedral geometry, with the overriding factor being the driving force for the molecule to assume the lowest energy geometry, which is readily accessible. Hydrocarbons containing only sp3 carbons are called alkanes and represent the simplest and least reactive class of organic compounds. You should note that "hybridization" is a simple mathematical process which is useful in modifying electron densities, as predicted from the classical hydrogen atom analysis, to allow bonding geometries and electron densities in more complex molecules to be described. Again, the driving force for "hybridization" is the formation of a bonding geometry with the lowest net potential energy, which is accessible by energetically feasible mEANS. The tendency of molecules to seek to form the lowest energy structures (i.e., the most stable reaction intermediate) is a commonly occurring theme in organic reactions and a knowledge of intermediate stability will often allow the direction of a reaction pathway to be accurately predicted. Two additional orbital hybrids are also available for carbon; one in which the 2s-orbital combines with two of the available p-orbitals (sp2) and a second in
which the 2s combines with one p(sp). The geometry predicted for the sp hybrid is trigonal with the unused p-orbital perpendicular to the plane. Carbons which are sp must be connected to at least one additional sp? atom and organic molecules containing one or more pairs of sp carbons are called alkenes. A model for the simplest alkene, ethene (or ethylene) is shown below. As the drawing shows, the hydrogens and the second carbon are attached to the sp: carbon by 120 bond angles. The p-orbital on each of the sp carbons each contain one electron ("split"between the top and bottom lobes)and the two adjacent p-orbitals are in a position to overlap with each other to form a T-bond in which electron density is concentrated between the atoms, in a diffuse orbital above and below the plane. The combination of the single bond, formed from the sp orbitals, and the T-bond, are represented as a carbon-carbon double bond. In this representation, the valence of carbon is still four, with the double bond counting for two. The final hybrid which is common in organic chemistry is constructed from one s- and one p-orbital, termed an sp-hybrid and has linear geometry, as shown below. The two remaining p-orbitals on each sp atom each participate in T-bond formation with an adjacent sp center and form a triple bond; one sigma bond and two T-bonds. The three types of hybridization which are encountered in carbon compounds are shown below for the molecules ethane (sp, an alkane), ethene (sp, an alkene) and ethyne(sp, an alkyne) in both ball-and-stick and space-filling format. 〈
which the 2s combines with one p (sp). The geometry predicted for the sp2 hybrid is trigonal with the unused p-orbital perpendicular to the plane. Carbons which are sp2 must be connected to at least one additional sp2 atom and organic molecules containing one or more pairs of sp2 carbons are called alkenes. A model for the simplest alkene, ethene (or ethylene) is shown below. As the drawing shows, the hydrogens and the second carbon are attached to the sp2 carbon by 120o bond angles. The p-orbital on each of the sp2 carbons each contain one electron ("split" between the top and bottom lobes) and the two adjacent p-orbitals are in a position to overlap with each other to form a -bond in which electron density is concentrated between the atoms, in a diffuse orbital above and below the plane. The combination of the single bond, formed from the sp2 orbitals, and the -bond, are represented as a carbon-carbon double bond. In this representation, the valence of carbon is still four, with the double bond counting for two. The final hybrid which is common in organic chemistry is constructed from one s- and one p-orbital, termed an sp-hybrid, and has linear geometry, as shown below. The two remaining p-orbitals on each sp atom each participate in -bond formation with an adjacent sp center and form a "triple bond"; one sigma bond and two -bonds. The three types of hybridization which are encountered in carbon compounds are shown below for the molecules ethane (sp3, an alkane), ethene (sp2, an alkene) and ethyne (sp, an alkyne) in both ball-and-stick and space-filling format
Alkane nomenclature Alkanes represent the simplest of the functional groups which are common in organic chemistry. An alkane contains only carbon and hydrogen(a hydrocarbon and contains only single bonds (termed a saturated hydrocarbon. Alkanes have the general formula CH, thus, an alkane with 10 carbons (n =10)will have 2(10)+2=22 hydrogens, or the molecular formula C,Hz. The root, or parent name for an unbranched alkane is taken directly from the number of carbons in the chain according to a scheme of nomenclature established by the International Union of Pure and Applied Chemistry(IUPAC), as shown Condensed Structure methane CHa CHCH propan CH: CH2CH3 pentane CH3(CH2)3CH: CH3(CH2).CH3 CH3(CH2):: octane CH3 (CH2)CH3 CH3(CH2)CH cane CH3 (CH2)3CH3 undecane CH3 (CH])9CH; decane CH(CH2)CH Hydrocarbons, however, are not restricted to linear, unbranched chains and there are often many possible orders in which a hydrocarbon with a given molecular formula can be constructed. Compounds having the same molecular
Alkane Nomenclature Alkanes represent the simplest of the functional groups which are common in organic chemistry. An alkane contains only carbon and hydrogen (a hydrocarbon) and contains only single bonds (termed a saturated hydrocarbon. Alkanes have the general formula CnH2n+2, thus, an alkane with 10 carbons (n = 10) will have 2(10) + 2 = 22 hydrogens, or the molecular formula C1 0H2 2. The root, or parent name for an unbranched alkane is taken directly from the number of carbons in the chain according to a scheme of nomenclature established by the International Union of Pure and Applied Chemistry (IUPAC), as shown below: Name Condensed Structure methane CH4 ethane CH3CH3 propane CH3CH2CH3 butane CH3(CH2)2CH3 pentane CH3(CH2)3CH3 hexane CH3(CH2)4CH3 heptane CH3(CH2)5CH3 octane CH3(CH2)6CH3 nonane CH3(CH2)7CH3 decane CH3(CH2)8CH3 undecane CH3(CH2)9CH3 dodecane CH3(CH2)10CH3 Hydrocarbons, however, are not restricted to linear, unbranched chains and there are often many possible orders in which a hydrocarbon with a given molecular formula can be constructed. Compounds having the same molecular
formula. which differ in the order of attachment of the individual atoms are called constitutional isomers. An example of the three possible constitutional isomers of pentane (CH) are shown below. 人 Although there are only three constitutional isomers for pentane, for alkanes having larger numbers of carbons, the number of isomers is staggering: for C,he there are over 4 billion possible constitutional isomers In order to be able to communicate chemical information it is essential to have a systematic set of rule defining nomenclature for organic compounds. As mentioned previously, the IUPAC system of nomenclature accomplishes this and the rules for naming linear and branched alkanes are given below The IUPAC name for an alkane is constructed of two parts: 1)a prefix (meth.. eth... prop.. etc )which indicates the number of carbons in the main, or parent, chain of the molecule, and 2) the suffix .. ane to For branched-chain alkanes, the name of the parent hydrocarbon is taken from the longest continuous chain of carbon atom Groups attached to the parent chain are called subs titue nts and are named based on the num ber of carbons in the longest chain of that substituent, and are numbered using the number of the carbon atom on the parent chain to which they are attached. In simple alkanes, substituents are called alkyl groups and are named using the prefix for the number of carbons in their main chan and the suffix.yl. For example, methyl, ethyl, propyl, dodecyl,etc CH3 -CH2 -CH-CH3 CH3 -CH2 -CH-CH2CH If the same substituent occurs more than once in a molecule, the num ber of each carbon of the parent
formula, which differ in the order of attachment of the individual atoms, are called constitutional isomers. An example of the three possible constitutional isomers of pentane (C5H1 2) are shown below. Although there are only three constitutional isomers for pentane, for alkanes having larger numbers of carbons, the number of isomers is staggering; for C30H6 2, there are over 4 billion possible constitutional isomers. In order to be able to communicate chemical information, it is essential to have a systematic set of rule defining nomenclature for organic compounds. As mentioned previously, the IUPAC system of nomenclature accomplishes this and the rules for naming linear and branched alkanes are given below: • The IUPAC name for an alkane is constructed of two parts: 1) a prefix (meth... eth... prop..., etc.) which indicates the number of carbons in the main, or parent, chain of the molecule, and 2) the suffix ...ane to indicate that the molecule is an alkane. • For branched-chain alkanes, the name of the parent hydrocarbon is taken from the longest continuous chain of carbon atoms. • Groups attached to the parent chain are called substituents and are named based on the number of carbons in the longest chain of that substituent, and are numbered using the number of the carbon atom on the parent chain to which they are attached. In simple alkanes, substituents are called alkyl groups and are named using the prefix for the number of carbons in their main chain and the suffix ...yl. For example, methyl, ethyl, propyl, dodecyl, etc. • If the same substituent occurs more than once in a molecule, the number of each carbon of the parent
rs is given and a multiplier sed to indicate the total number of identical substituents; i.e., dimethyL. trimethyl. tetraethy L., etc 2, 3-dimethy Butane 2, 3, 4-trime thy pentane Numbering of the carbons in the parent chain is always done in the direction that gives the lowest number to the subs tituent whic h is encountered first, or, the lowest number at the first point of difference. If there are different substituents at equivalent positions on the cha in, the substituent of lower alphabeticalorder is given the lowest num ber. 3-ethy Heptane not 5-ethy Heptane 3-ethy1-5-methy Heptane not 5-ethy1-3-methy Thept In constructing the name, substituents are arranged in alphabetical order, without regard for ultipl 2, 2, 5-trimethy Hexane 2, 3, 5-trimethy Hexane t255-trime thy The 2,4 5-trimethy Hexane For complex molecules, the IUPAC system of nomenclature can generate somewhat bewildering, and equally complex nomenclature. This is further complicated by the fact that many common molecules are routinely referred to using simple names which are descriptive of the molecule, or have arisen historically. The most common examples of these are the substituent names for side-chains containing three to five carbons, where the prefixes iso.,sec. are commonly used. The structures corresponding to these substituents are shown below Common Substituent names CH,CH, CH ropy l CHCH(CH3 )2 butyl CH, CH2 CH isobutyl CH2CHCH(CH3)
chain where the substituent occurs is given and a multiplier is used to indicate the total number of identical substituents; i.e., dimethyl... trimethyl... tetraethyl..., etc. • Numbering of the carbons in the parent chain is always done in the direction that gives the lowest number to the substituent which is encountered first, or, the lowest number at the first point of difference. If there are different substituents at equivalent positions on the chain, the substituent of lower alphabetical order is given the lowest number. • In constructing the name, substituents are arranged in alphabetical order, without regard for multipliers. For complex molecules, the IUPAC system of nomenclature can generate somewhat bewildering, and equally complex nomenclature. This is further complicated by the fact that many common molecules are routinely referred to using simple names which are descriptive of the molecule, or have arisen historically. The most common examples of these are the substituent names for side-chains containing three to five carbons, where the prefixes iso..., sec-..., tert-..., and neo are commonly used. The structures corresponding to these substituents are shown below: Common Substituent Names: propyl -CH2CH2CH3 isopropyl -CHCH(CH3)2 butyl -CH2CH2CH3 isobutyl -CH2CHCH(CH3)2
H(CH; CH CH3 tertbutyl C(CH3 ) When these descriptors are used in an IUPAC name, iso is alphabetized normally the hyphenated prefixes, however (sec- and tert-)are disregarded when alphabetizing A more systematic method for the nomenclature of side-chains involves identifying the longest chain in the substituent, numbering the substituent from the point of attachment to the parent, and indicating side-chains on the substituent using the standard me thod described for simple alkanes. The name is enclosed in parenthesis to indicate that the numbering corresponds to the local side-chain, not the parent chain. Thus: an isopropyl side-chain can also be named(1-methylethyl), a sec-butyl side-chain can also be named(I-methylpropy l), an isopentyl side-cha in can also be named (3-methy butyl), etc CH-CH -CH-CHa-CH H CH -methy lpropy D) or-(1, 1-dimethy lathy D) CH2-CH2-CH-CH. H2-CH-CH2-CH As a student of organic chemistry, you will encounter a variety of nomenclature conventions, and many non-standard names in common usage must simply be learned. Systematic nomenclature, however, is important to clearly understand as these hods are utilized in the cataloging of chemical inf int and computerized databases and effective information retrieval requires a good working knowledge of these methods The origin of the prefixes sec-and tert-, given above, rests with an attempt to describe the nature of the branched carbon unit. By definition, a primary carbon is one which is attached to one other carbon atom, a secondary carbon is one which is attached to two, a tertiary carbon is attached to three, and quaternary carbon is attached to four other carbon atoms; these are often abbreviated as 1, 2, 3 and 4. carbons
sec-butyl -CH(CH3)CH2CH3 tert-butyl -C(CH3)3 When these descriptors are used in an IUPAC name, iso is alphabetized normally; the hyphenated prefixes, however (sec- and tert-) are disregarded when alphabetizing. A more systematic method for the nomenclature of side-chains involves identifying the longest chain in the substituent, numbering the substituent from the point of attachment to the parent, and indicating side-chains on the substituent using the standard method described for simple alkanes. The name is enclosed in parenthesis to indicate that the numbering corresponds to the local side-chain, not the parent chain. Thus: • an isopropyl side-chain can also be named (1-methylethyl), • a sec-butyl side-chain can also be named (1-methylpropyl), • an isopentyl side-chain can also be named (3-methylbutyl), etc. As a student of organic chemistry, you will encounter a variety of nomenclature conventions, and many non-standard names in common usage must simply be learned. Systematic nomenclature, however, is important to clearly understand as these methods are utilized in the cataloging of chemical information in print and computerized databases and effective information retrieval requires a good working knowledge of these methods. The origin of the prefixes sec- and tert-, given above, rests with an attempt to describe the nature of the branched carbon unit. By definition, a primary carbon is one which is attached to one other carbon atom, a secondary carbon is one which is attached to two, a tertiary carbon is attached to three, and a quaternary carbon is attached to four other carbon atoms; these are often abbreviated as 1o, 2o, 3o and 4o carbons
secondary -CH2-CH-CH2-C--CH3 Conformations of Alkanes Cycloalkanes Structural formulas are useful for showing the attachment of atoms, and three-dimensional drawings are useful for showing molecular shapes. Neither of these, however, conveys much information regarding the dynamics of molecular conformations and the role that these play in controlling equilibrium shapes and reactivity of organic molecules. As mentioned previously, there is generally free rotation around carbon-carbon single bonds. At room temperature, this rotation can be quite rapid and can occur with a rate constant of *10 sec4. For ethane, this rotation has only a small intrinsic energy barrier since the van der Waals radius of the hydrogen atoms on the adjacent carbons is sufficiently small so that overlap is minimal. A movie file demonstrating this rotation is shown below (Click on the icon above to view the movie: use the BAcK button to return to this page) This can be contrasted. however, with rotation around the central carbon-carbon bond in butane, shown in the movie panel below, in which two methyl groups clearly overlap during a single rotat ion (the van der Waals radii of the methyl hydrogen atoms clearly overlap)
Conformations of Alkanes & Cycloalkanes Structural formulas are useful for showing the attachment of atoms, and three-dimensional drawings are useful for showing molecular shapes. Neither of these, however, conveys much information regarding the dynamics of molecular conformations and the role that these play in controlling equilibrium shapes and reactivity of organic molecules. As mentioned previously, there is generally free rotation around carbon-carbon single bonds. At room temperature, this rotation can be quite rapid and can occur with a rate constant of 108 sec-1. For ethane, this rotation has only a small intrinsic energy barrier since the van der Waals radius of the hydrogen atoms on the adjacent carbons is sufficiently small so that overlap is minimal. A movie file demonstrating this rotation is shown below: (Click on the icon above to view the movie; use the BACK button to return to this page) This can be contrasted, however, with rotation around the central carbon-carbon bond in butane, shown in the movie panel below, in which two methyl groups clearly overlap during a single rotation (the van der Waals radii of the methyl hydrogen atoms clearly overlap)