1149 环烷烃的构象■ 1、环丙烷的构象 CH2 图5-2 环丙烷的弯曲键 图 环丙烷中的重叠式构象 eclipsed H's eclipsed H's eclipsed H's 12:side view of cyclopropane 17
17 三、环烷烃的构象 1、环丙烷的构象 CH2 图 环丙烷中的重叠式构象 图5-2 环丙烷的弯曲键 C C C 114 O 105.5 O H H H H H H
H 扭转张力增如 H 图5-5 扭转张力 交叉式构象 重叠式构象 2.环丁烷和环戊烷的构象 环丁烷的构象 18
18 交叉式构象 重叠式构象 H H H H H H 扭转张力增加 H H H H H H 图5-5 扭转张力 2. 环丁烷和环戊烷的构象 环丁烷的构象
Cyclobutane g里 Angle strain due to compression Torsional strain partially relieved by ring- puckering not quite eclipsed H 109.59 tetrahedral angle 19.5° angle H not quite eclipsed 90°· compression Newman projection of one bond
19 Cyclobutane ❖Angle strain due to compression ❖Torsional strain partially relieved by ringpuckering
HTHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHF
20
Cyclopentane If planar,,angles would be108°，but all hydrogens would be eclipsed. Puckered conformer reduces torsional strain. H H H H H H “fiap" H folded Newman projection upward showing relief of viewed eclipsing of bonds from
21 Cyclopentane ❖If planar, angles would be 108, but all hydrogens would be eclipsed. ❖Puckered conformer reduces torsional strain. =>