Cycloalkane Stability -5-and 6-membered rings most stable -Bond angle closest to 109.5 Angle(Bayer）)strain -Preferential Conformation -Measured by heats of combustion per -CH2-
Cycloalkane Stability ▪5- and 6-membered rings most stable ▪Bond angle closest to 109.5 ▪Angle (Bayer) strain ▪Preferential Conformation ▪Measured by heats of combustion per -CH2 -
Bayer张力学说 1885年A.Von Bayer提出了张力学说。他根据碳是正四面体的模型，并假定 成环后，所有碳原子都在同一平面上，于是得出如下的结论：如果成环后所 有碳原子的每两键间的正常键角是109.5°(109°28')，那么不但这种环 很容易形成，而且生成的环状化合物也是很稳定的。 Angle strain,also called Baeyer strain in cyclic molecules,is the resistance associated with bond angle compression or bond angle expansion.1 It occurs when bond angles deviate from the ideal bond angles to achieve maximum bond strength in a specific chemical conformation.Angle strain typically affects cyclic molecules because non-cyclic molecules will thermodynamically conform to the most favorable stable state
Bayer张力学说 1885年A.Von Bayer提出了张力学说。他根据碳是正四面体的模型，并假定 成环后，所有碳原子都在同一平面上，于是得出如下的结论：如果成环后所 有碳原子的每两键间的正常键角是109.5°（109°28′），那么不但这种环 很容易形成，而且生成的环状化合物也是很稳定的。 Angle strain, also called Baeyer strain in cyclic molecules, is the resistance associated with bond angle compression or bond angle expansion.1 It occurs when bond angles deviate from the ideal bond angles to achieve maximum bond strength in a specific chemical conformation. Angle strain typically affects cyclic molecules because non-cyclic molecules will thermodynamically conform to the most favorable stable state
Ring Strain in Cycloalkanes Baeyer Strain Theory In 1885 Adolf Von Baeyer (of the University of Munich)proposed a strain theory according to which the deviation of bond angles from a normal tetrahedral value causes,the strain in the molecules which makes them unstable as compared to the molecules with tetrahedral angle.For example in cyclopropane or cyclobutane the rings are planar with ring bond angles of 60 and 90 respectively.This implies that the normal C-C bond has to be compressed from 109 28'to 60 or 90 to fit the geometry of the ring.This explains the reactivity of these rings towards the reaction that cause ring opening to form open chain compounds to relive the angle strain. Johann Friedrich Wilhelm Adolf von Baeyer First graduate student of Kekule' Developed theory that cycloalkanes possess different amounts of strain or stability,depending on the size of the ring. Awarded Nobel Prize in 1905 for work with organic dyes. Total synthesis of indigo. "I have never set up an experiment to see whether I was right,but to see how the materials behave
Ring Strain in Cycloalkanes Baeyer Strain Theory In 1885 Adolf Von Baeyer (of the University of Munich) proposed a strain theory according to which the deviation of bond angles from a normal tetrahedral value causes, the strain in the molecules which makes them unstable as compared to the molecules with tetrahedral angle. For example in cyclopropane or cyclobutane the rings are planar with ring bond angles of 60° and 90° respectively. This implies that the normal C – C bond has to be compressed from 109°28’ to 60° or 90° to fit the geometry of the ring. This explains the reactivity of these rings towards the reaction that cause ring opening to form open chain compounds to relive the angle strain. Johann Friedrich Wilhelm Adolf von Baeyer • First graduate student of Kekule’ • Developed theory that cycloalkanes possess different amounts of strain or stability, depending on the size of the ring. • Awarded Nobel Prize in 1905 for work with organic dyes. • Total synthesis of indigo. "I have never set up an experiment to see whether I was right, but to see how the materials behave
从下图可以看出，在形成双键时（二员环）每键要向内屈挠 109°28′/2=54°441 109.5° 104 4 (109.5°-609/2=2044 (109°28′-60°)/2=20°44
从下图可以看出，在形成双键时（二员环）每键要向内屈挠 109°28′/2 = 54°44′ （109°28′-60°）/2=20°44′
Cyclopropane -Large ring strain due to angle compression -Very reactive,weak bonds H H l09.5°tetrahedral angle 60° 49.5°angle compression H H “bent bonds'" nonlinear overlap
Cyclopropane ▪Large ring strain due to angle compression ▪Very reactive, weak bonds