厦门大学化学化工学院：《有机化学》课程教学资源（课件讲稿，双语版）第四章 烷烃 命名 构象分析及合成导论（4.8-4.20）Sigma Bonds and Bond Rotation

ORGANIC CHEMISTRY Chapter 4 4.8 Sigma Bonds and bond Rotation Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 4 4.8 Sigma Bonds and Bond Rotation

ORGANIC CHEMISTRY Chapter 4 o The different arrangements of atoms caused b rotation about a single bond are called conformations A s of the molecule, and a specific conformation is called a conformer(构象异构体, conformation Isomer) o an analysis of the energy changes that a molecule undergoes as groups rotate about single bonds Is called a conformational analysis(构象分析 o Unlike constitutional isomers, though, different conformers can't usually be isolated because they interconvert too rapidly Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 4 The different arrangements of atoms caused by rotation about a single bond are called conformations (构象)of the molecule, and a specific conformation is called a conformer (构象异构体, conformation isomer). An analysis of the energy changes that a molecule undergoes as groups rotate about single bonds is called a conformational analysis (构象分析). Unlike constitutional isomers, though, different conformers can’t usually be isolated because they interconvert too rapidly

ORGANIC CHEMISTRY Chapter 4 Conformations of ethane Representations of conformers o Newman projections( Newman投影式) Sawhorse(锯架式) o Wedge-dash(虚线楔线式,伞式) H H H、 H H H H H H H H H H H Newman projections Sawhorse Wedge-dash Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 4 Conformations of Ethane Representations of conformers Newman projections (Newman 投影式) Sawhorse (锯架式) Wedge-dash (虚线-楔线式 伞式) H H H H H H H H H H H H H H H H H H Newman projections Sawhorse Wedge-dash

ORGANIC CHEMISTRY Chapter 4 The staggered Conformation and the eclipsed Conformation(交叉式构象与重叠式构象) H 60 H H H H H H 重叠式构象个 交叉式构象 E closed Staggered The least stable conformation The most stabl conformation Torsional barrier(转动能垒)12.1kJmo1 Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 4 The Staggered Conformation and the Eclipsed Conformation (交叉式构象与重叠式构象) H H H H H H H H H H H H 重叠式构象 交叉式构象 60O Eclipsed Staggered The least stable conformation The least stable conformation The most stable conformation The most stable conformation Torsional barrier(转动能垒) 12.1 kJ·mol-1

ORGANIC CHEMISTRY Chapter 4 Conformational analysis of ethane 2.29A H H o Bond length: CH1.07, C--C154A o Bond angle:∠HCH1095 o The distance between two h atomS: 2, A o tomic radius of H: H=1.2 A Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 4 Conformational analysis of ethane H H H H H H 2.29 A Bond length C—H 1.07, C—C 1.54 Å Bond angle HCH 109.5 The distance between two H atoms 2.29 Å tomic radius of H γH = 1.2 Å

ORGANIC CHEMISTRY Chapter 4 Potential energy diagram for rotation about the cc bond in ethane 重叠式构象 E 交叉式构象 H H H HCHH HH H H H H H H H 12. 1 kJ/mol 60° 120° 180 240旋转角度 Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 4 Potential energy diagram for rotation about the C—C bond in ethane 60 120 180 240 E H H H H H H H H H HH H 重叠式构象 交叉式构象 H H H H H H H H H HH H 12.1 kJ / mol 旋转角度

ORGANIC CHEMISTRY Chapter 4 4.9 Conformational Analysis of Butane Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 4 4.9 Conformational Analysis of Butane

ORGANIC CHEMISTRY Chapter 4 CH CH CH CH 600H CH 360 600 H H H 了b H ChBH 3 全重叠式 邻位交叉式 部分重叠式 Eclipsed Gauche Eclipsed CH The least stable conformation H、 H H H CH The most stable conformation 对位交叉式 优势构象 Anti Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 4 H CH3 H H H CH3 CH3 H H H H CH3 全重叠式 邻位交叉式 部分重叠式 H H H CH3H CH3 H CH3 H H H CH3 H H CH3 H H CH3 CH3 H H H H CH3 1 2 3 4 5 6 对位交叉式 部分重叠式 邻位交叉式 60O 60O 60O 60O 60O Eclipsed Gauche Anti Eclipsed Eclipsed Gauche The least stable conformation The least stable conformation The most stable conformation 优势构象 The most stable conformation 优势构象

ORGANIC CHEMISTRY Chapter 4 Energy changes that arise from rotation about the c2-c3 bond of butane CH CH CH3 H 1 H 5 个HH CH3 CH CH CH H H CB◇ H 2 6 CH3 4 3.7 kJ/mol 15.9 kJ/mol 18.8 kJ/mol 120 240 300 360 旋转角度 Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 4 Energy changes that arise from rotation about the C2—C3 bond of butane 60 120 180 240 300 360 E 3.7 kJ/mol 15.9 kJ/mol 18.8 kJ/mol CH3 H H H H CH3 CH3 H H HH CH3 H H H CH3H CH3 H CH3 HH H CH3 H H CH3 H H CH3 CH3 H H H H CH3 1 2 3 4 5 6 CH3 H H HH CH3 1 旋转角度

ORGANIC CHEMISTRY Chapter 4 Compounds Anti conformations (%) CICH, CHCI 70 Brchchobr 84~91 PhcHochoPh >90 H O H H H H H H Department of Chemistry, Xiamen University

ORGANIC CHEMISTRY Department of Chemistry, Xiamen University Chapter 4 Compounds Anti conformations (%) ClCH2CH2Cl ~70 BrCH2CH2Br 84~91 PhCH2CH2Ph >90 H O H H H Cl H H O H H H O H H