Conformations of Butane 女人因术女人因 Gauche Gauche Anti 60 60 2 Ant Dihedral ne between ■ anti conformation has two methyl groups 180away from each other ■ Rotation around the C2-C3 gives eclipsed conformation ■ Staggered conformation with methyl groups 60apart (causing steric strain)is gauche conformation
Conformations of Butane anti conformation has two methyl groups 180° away from each other Rotation around the C2–C3 gives eclipsed conformation Staggered conformation with methyl groups 60° apart (causing steric strain) is gauche conformation
Stability of Cycloalkanes since carbon prefers to 120 have bond angles of ~109°，ring sizes other than five and six are highly strained (angle strain) 40 ■ Rings are strained due to bond bending distortions 34567891011121314 and steric interactions Ring size l09°(tetrahedral 19 *499 90 1089 Cyclopropane Cyclobutane Cyclopentane 2004 Thomson-Brooks/Cole
Stability of Cycloalkanes since carbon prefers to have bond angles of ~109°, ring sizes other than five and six are highly strained (angle strain ) Rings are strained due to bond bending distortions and steric interactions
The Nature of Ring Strain ■ Rings larger than 3 atoms are not flat Cyclic molecules can assume nonplanar conformations to minimize angle strain and torsional strain by ring- puckering (a) (b) H (c)Not quite eclipsed H H H H H H H H Not quite eclipsed Larger rings have many more possible conformations than smaller rings and are more difficult to analyze
The Nature of Ring Strain Rings larger than 3 atoms are not flat Cyclic molecules can assume nonplanar conformations to minimize angle strain and torsional strain by ringpuckering Larger rings have many more possible conformations than smaller rings and are more difficult to analyze