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):第五章.脂环烃授课类型理论课 Cycloalkanes 第6周第17-22 授课时间 教学目标或要求∶了解脂环烃的结构,分类和命名以及脂环烃的化学性质。掌握环己 烷的构象。 教学内容(包括基本内容、重点、难点) Cycloalkane Nomenclature The ability of carbon to form bonds with itself allows for the possibility of the formation of cyclic compounds. In nature, cyclic compounds with ring sizes from 3 to 30 carbons are known; five- and six-member rings are especially common For a simple cycloalkane the general molecular formula is CHa, where n is the total number of carbons. You will note that this differs from the general formula for an alkane(C, H)by the lack of the two additional hydrogens(the"+2 term") As a general rule, every ring which is constructed from an alkane reduces the number of hydrogens in the molecular formula for the parent hydrocarbon by 2. Thus one ring gives CHa, two rings within the molecule would give a molecular formula of the type CHasn, three rings, CH, etc. Thus by simply examining the molecular formula of an alkane or cycloalkane, you can immediately calculate the number of rings within the molecule. Th ion can be expanded to also include double bonds (which also reduce the number of hydrogens in an alkane by two) to give the concept of degree of unsaturation, which is covered in a later section. Using this simple calculation, the total number of rings and multiple bonds in a molecule can be calculated, based simply on the observed molecular formula. Molecular models of cycloalkanes with n=3 to 7 are shown below. You should note that, in the smaller ring sizes (3, 4 and 5), the bond angles are significantly less than the optimal 109. 5 This results in a significant amount of ring strain in these compounds which make many small rings susceptible to ring-opening reactions. The bond angles in a six-membered ring match well with the tetrahedral geometry of carbon and there is virtually no ring strain in these compounds. Rings which are seven-membered and larger are
有机化学(双语教学) 课程教案 授课题目（教学章节或主题）：第五章．脂环烃 (Cycloalkanes) 授课类型 理论课 授课时间 第 6 周第 17-22 节 教学目标或要求：了解脂环烃的结构，分类和命名以及脂环烃的化学性质。掌握环己 烷的构象。 教学内容（包括基本内容、重点、难点）： Cycloalkane Nomenclature The ability of carbon to form bonds with itself allows for the possibility of the formation of cyclic compounds. In nature, cyclic compounds with ring sizes from 3 to 30 carbons are known; five- and six-member rings are especially common. For a simple cycloalkane the general molecular formula is CnH2 n, where n is the total number of carbons. You will note that this differs from the general formula for an alkane (CnH2n+2) by the lack of the two additional hydrogens (the "+ 2 term"). As a general rule, every ring which is constructed from an alkane reduces the number of hydrogens in the molecular formula for the parent hydrocarbon by 2. Thus one ring gives CnH2 n, two rings within the molecule would give a molecular formula of the type CnH2 n-2, three rings, CnH2 n-4, etc. Thus by simply examining the molecular formula of an alkane or cycloalkane, you can immediately calculate the number of rings within the molecule. This notion can be expanded to also include double bonds (which also reduce the number of hydrogens in an alkane by two) to give the concept of degree of unsaturation, which is covered in a later section. Using this simple calculation, the total number of rings and multiple bonds in a molecule can be calculated, based simply on the observed molecular formula. Molecular models of cycloalkanes with n = 3 to 7 are shown below. You should note that, in the smaller ring sizes (3, 4 and 5), the bond angles are significantly less than the optimal 109.5o. This results in a significant amount of ring strain in these compounds which make many small rings susceptible to ring-opening reactions. The bond angles in a six-membered ring match well with the tetrahedral geometry of carbon and there is virtually no ring strain in these compounds. Rings which are seven-membered and larger are
highly distorted, and again display significant ring strain. The nomenclature for a simple cycloalkane is based on the parent hydrocarbon with the simple addition of the prefix cyclo. a three-membered ring is therefore cyclopropane, four-membered, cyclobutane, five-membered, cyclopentane, six-membered, cyclohexane, etc. HH H alkane five carbons As a convenient shortcut, cyclic structures are usually drawn using line (structural or line-angle) drawings, as shown above. Again, it is important to understand that every vertex in these drawings represents a-CH: group, every truncated line a -CH, group and intersections of three or four lines represent 3 or 4 carbons, respectively. Substituents on cycloalkanes are named using the conventions described for alkanes, with the exception that, on rings bearing only one substituent, no number is needed; otherwise numbering proceeds to produce the lowest number at the first point of difference
highly distorted, and again display significant ring strain. The nomenclature for a simple cycloalkane is based on the parent hydrocarbon, with the simple addition of the prefix cyclo. A three-membered ring is therefore cyclopropane, four-membered, cyclobutane, five-membered, cyclopentane, six-membered, cyclohexane, etc. As a convenient shortcut, cyclic structures are usually drawn using line (structural or line-angle) drawings, as shown above. Again, it is important to understand that every vertex in these drawings represents a -CH2- group, every truncated line a -CH3 group and intersections of three or four lines represent 3 o or 4o carbons, respectively. Substituents on cycloalkanes are named using the conventions described for alkanes, with the exception that, on rings bearing only one substituent, no number is needed; otherwise numbering proceeds to produce the lowest number at the first point of difference
.CHs H3 methylcyclopropane 1.2-dimethylcyclopentane 1, 1-dimethylcyclohexane CH3 CH3CH2 l-ethy l-4-methy cyc lohe imethy cyclohexane (assign numbers to give lowest number at first point of difference; arrange alphabetically) CH3 1-ethy 1-1 me thy cycloheptane 1-cyclopropy 1-1-methy cyclohexane Polycyclic carbons, such as those shown below, are common in organic chemistr Carbons in these compounds which are shared between attached rings are termed bridgehead carbons, and, in the special case where only one carbon is shared between rings, the bridging carbon is referred to as a spiro carbon. Polycyclic compounds are named and numbered using a complex system to indicate ring sizes and attachments, and will be covered later. 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. ed previously, there is generally free rotation around carbon-carbon ingle bonds. At room temperature, this rotation can be quite rapid and can occur with a rate constant of *10 sec. 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
Polycyclic carbons, such as those shown below, are common in organic chemistry. Carbons in these compounds which are shared between attached rings are termed bridgehead carbons, and, in the special case where only one carbon is shared between rings, the bridging carbon is referred to as a spiro carbon. Polycyclic compounds are named and numbered using a complex system to indicate ring sizes and attachments, and will be covered later. 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 me l gro clearly overlap during a single rotation(the van der Waals radii of the methyl hydrogen atoms clearly overlap) s3 keal/m The rotation around the single bond in ethane, while not obviously hindered, does generate conformational isomers having different potential energies. As shown above, as the dihedral angle between the ethane hydrogen atoms changes from 60(a staggered conformation) to 120(an eclipsed conformation),the potential energy of the molecule increases by about 3 kcal/mole. As the me l group continues to rotate towards 180, the potential energy again drops and rises again as the next eclipsed structure is formed
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). The rotation around the single bond in ethane, while not obviously hindered, does generate conformational isomers having different potential energies. As shown above, as the dihedral angle between the ethane hydrogen atoms changes from 60 (a staggered conformation) to 120 (an eclipsed conformation), the potential energy of the molecule increases by about 3 kcal/mole. As the methyl group continues to rotate towards 180 , the potential energy again drops and rises again as the next eclipsed structure is formed
eclipsed eclipsed eclipsed gauche 3.5 koa 0.9k The effect of rotation on the potential energy of butane around the central carbon-carbon bond is more significant, as shown above. The structure shown at Oo is fully eclipsed, that is, both methyl groups are aligned and are interacting maximally. As the front me thyl group is rotated 60 a gauche conformation is produced in which the methy l group is nestled between the back methy l and the adjacent hydrogen atom. Another 60 rotation produces an eclipsed version of the gauche conformation which is approximately 2.4 kcal/mole less stable. At 180, the anti conformation is formed in which the two methyl groups are on opposite faces of the molecule and no groups are eclipsed. This is the most stable confomer and it differs from the fully eclipsed confomer by about 5 kcal/mole in potential energy. Further rotations regenerate an equivalent eclipsed gauche conformer (at 240), another gauche form(300) and finall the eclipsed form at 360. These rotations are best seen in a movie clip which can be accessed by clicking on the icon below (Click on the icon above to view the movie) Rotations such as these are not possible in cycloalkanes, where the ring constrains the movements around the carbon-carbon single bonds. Cyclopropane rings are generally flat and have little conformational flexibility. The flexibility of four-and five-membered rings is significantly greater and these molecules exist as a dynamic equilibrium among various puckered
The effect of rotation on the potential energy of butane around the central carbon-carbon bond is more significant, as shown above. The structure shown at 0o is fully eclipsed, that is, both methyl groups are aligned and are interacting maximally. As the front methyl group is rotated 60o, a gauche conformation is produced in which the methyl group is nestled between the back methyl and the adjacent hydrogen atom. Another 60o rotation produces an eclipsed version of the gauche conformation which is approximately 2.4 kcal/mole less stable. At 180o, the anti conformation is formed in which the two methyl groups are on opposite faces of the molecule and no groups are eclipsed. This is the most stable confomer and it differs from the fully eclipsed confomer by about 5 kcal/mole in potential energy. Further rotations regenerate an equivalent eclipsed gauche conformer (at 240o), another gauche form (300o) and finally, the eclipsed form at 360o. These rotations are best seen in a movie clip which can be accessed by clicking on the icon below: (Click on the icon above to view the movie) Rotations such as these are not possible in cycloalkanes, where the ring constrains the movements around the carbon-carbon single bonds. Cyclopropane rings are generally flat and have little conformational flexibility. The flexibility of four- and five-membered rings is significantly greater and these molecules exist as a dynamic equilibrium among various "puckered
conformations, as shown below The dynamic flexibility of a five-membered ring is best visualized in the movi clip(below) which simulates the equilibrium interconversion of the various conformational isomers (Click on the icon above to view the movie) hair"cyclohexane ir"cyclohexane axial substituents The conformational flexibility of cyclohexane is somewhat unique in that two equivalent structures are involved which are linked by a process termed ring inversion. As shown in the figure above, the lowest energy conformation of cyclohexane is one in which each end of the molecule is puckered", relative to the plane of the ring. This form is commonly called the chair conformation as it somewhat resembles a reclined lawn chair. Inspection of this structure shows that there are two types of hydrogens in the molecule; a set that is perpendicular to the plane of the ring(axial hydrogens)and a set which are more-or-less in the plane of the ring (equatorial hydrogens). The chemical reactivity of cyclohexane, however, is inconsistent with two types of hydrogens in a stable form of the molecule (for example, there is only one monochlorocyclohexane, not two, as would be predicted if axial and equatorial hydrogens could be replaced independently). The explanation for this fact is that the flexibility of cyclohexane allows for rapid ring inversion, in which
conformations, as shown below. The dynamic flexibility of a five-membered ring is best visualized in the movie clip (below) which simulates the equilibrium interconversion of the various conformational isomers. (Click on the icon above to view the movie) The conformational flexibility of cyclohexane is somewhat unique in that two equivalent structures are involved which are linked by a process termed "ring inversion". As shown in the figure above, the lowest energy conformation of cyclohexane is one in which each end of the molecule is "puckered", relative to the plane of the ring. This form is commonly called the "chair conformation", as it somewhat resembles a reclined lawn chair. Inspection of this structure shows that there are two types of hydrogens in the molecule; a set that is perpendicular to the plane of the ring (axial hydrogens) and a set which are more-or-less in the plane of the ring (equatorial hydrogens). The chemical reactivity of cyclohexane, however, is inconsistent with two types of hydrogens in a stable form of the molecule (for example, there is only one monochlorocyclohexane, not two, as would be predicted if axial and equatorial hydrogens could be replaced independently). The explanation for this fact is that the flexibility of cyclohexane allows for rapid ring inversion, in which
one chair conformation is replaced by a second. Intermediate between these two chair forms is an unstable conformation called boat cyclohexane", in which both ends of the molecule are puckered in the same direction. The important thing to note about the process of ring inversion is that during ring inversion, all axial substituents are converted to equatorial substituents, and all uatorial substituents become axial. This process is difficult to visualize initially, without the use of molecular models, but can be seen easily in the movie clip below. lClick on the icon above to view the movie) axial hydrogens in cyclohexane experience a slight amount of steric ulsion. More bulky groups, however, can interact strongly with other axial substituents, making it energetically unfavorable for these groups to occupy axial positions. These unfavorable interactions can be seen below in the equatorial and axial representations of bromocyclohexane. Bromocyclohexane in Equatorial and Axial Conformations In the equatorial conformation, the bromine is sticking out from the plane of the ring and is experiencing only minimal steric interactions with neighboring groups. In the axial conformation, however, the van der Waals radii of the bromine significantly overlaps with that of the two axial hydrogens. This type of steric interaction can also be clearly seen in the models for ethy cyclohexane, shown be low
one chair conformation is replaced by a second. Intermediate between these two chair forms is an unstable conformation called "boat cyclohexane", in which both ends of the molecule are puckered in the same direction. The important thing to note about the process of ring inversion is that during ring inversion, all axial substituents are converted to equatorial substituents, and all equatorial substituents become axial. This process is difficult to visualize, initially, without the use of molecular models, but can be seen easily in the movie clip below. (Click on the icon above to view the movie) The axial hydrogens in cyclohexane experience a slight amount of steric repulsion. More bulky groups, however, can interact strongly with other axial substituents, making it energetically unfavorable for these groups to occupy axial positions. These unfavorable interactions can be seen below in the equatorial and axial representations of bromocyclohexane. In the equatorial conformation, the bromine is "sticking out" from the plane of the ring and is experiencing only minimal steric interactions with neighboring groups. In the axial conformation, however, the van der Waals radii of the bromine significantly overlaps with that of the two axial hydrogens. This type of steric interaction can also be clearly seen in the models for ethylcyclohexane, shown below
Note van der Waals Interactions The full rotation of the ethy l group is also shown in the movie clip shown below Click on the icon above to view the movie As stated above, steric interactions tend to make conformations containing axial substituents energetically unfavorable, relative to placing these substituents in equatorial positions. Since axial and equatorial groups in cyclohexane are linked via equilibria involving ring inversion, the net effect is to force the equilibrium towards the more stable form in which the bulky substituents are in equatorial positions, as shown below. For very large substituents (i.e, the tert-butyl group) this equilibrium is so strongly shifted so that ring inversion essentially never occurs. Such groups are said to" lock the ring into the energetically favorable conformation
The full rotation of the ethyl group is also shown in the movie clip shown below. (Click on the icon above to view the movie) As stated above, steric interactions tend to make conformations containing axial substituents energetically unfavorable, relative to placing these substituents in equatorial positions. Since axial and equatorial groups in cyclohexane are linked via equilibria involving ring inversion, the net effect is to force the equilibrium towards the more stable form in which the bulky substituents are in equatorial positions, as shown below. For very large substituents (i.e., the tert-butyl group) this equilibrium is so strongly shifted so that ring inversion essentially never occurs. Such groups are said to "lock" the ring into the energetically favorable conformation
教学手段与方法:课堂讲授 思考题、讨论题、作业:( Homeworks; Page161 Additional Problems,4.15-434 参考资料(含参考书、文献等): 1. Solomons, Organic Chemistry, fifth adition 2. Oxford; Organic Chemistry 3.北京大学,有机化学 4.南京大学,有机化学,(上,下) 5.邢其毅,有机化学,(上,下) 注:1、每项页面大小可自行添减;2一次课为一个教案;3、“重点”、“难点”、“教学手段 与方法”部分要尽量具体;4、授课类型指∶理论课、讨论课、实验或实习课、练习或习题 课等
教学手段与方法：课堂讲授 思考题、讨论题、作业：(Homeworks;Page161.Additional Problems;4.15-4.34) 参考资料（含参考书、文献等）： 1. Solomons, Organic Chemistry, fifth adition 2. Oxford; Organic Chemistry 3. 北京大学， 有机化学 4．南京大学， 有机化学，（上，下） 5．邢其毅，有机化学， （上，下） 注：1、每项页面大小可自行添减；2 一次课为一个教案；3、“重点”、“难点”、“教学手段 与方法”部分要尽量具体；4、授课类型指：理论课、讨论课、实验或实习课、练习或习题 课等