Free rotation about `color{red}(CโC)` single bond is possible because of symmetric electron distribution of the sigma molecular orbital around the internuclear axis of the `color{red}(CโC)` bond which is not disturbed due to rotation about its axis. This rotation results into different spatial arrangements of atoms in space which can change into one another.
`color{green}("๐๐ฎ๐๐ก ๐ฌ๐ฉ๐๐ญ๐ข๐๐ฅ ๐๐ซ๐ซ๐๐ง๐ ๐๐ฆ๐๐ง๐ญ๐ฌ ๐จ๐ ๐๐ญ๐จ๐ฆ๐ฌ ๐ฐ๐ก๐ข๐๐ก ๐๐๐ง ๐๐ ๐๐จ๐ง๐ฏ๐๐ซ๐ญ๐๐ ๐ข๐ง๐ญ๐จ")` `color{green}("๐จ๐ง๐ ๐๐ง๐จ๐ญ๐ก๐๐ซ ๐๐ฒ ๐ซ๐จ๐ญ๐๐ญ๐ข๐จ๐ง ๐๐ซ๐จ๐ฎ๐ง๐ ๐ ")` `color{green}("๐-๐ ๐ฌ๐ข๐ง๐ ๐ฅ๐ ๐๐จ๐ง๐ ๐๐ซ๐ ๐๐๐ฅ๐ฅ๐๐ ๐๐จ๐ง๐๐จ๐ซ๐ฆ๐๐ญ๐ข๐จ๐ง๐ฌ ๐จ๐ซ ๐๐จ๐ง๐๐จ๐ซ๐ฆ๐๐ซ๐ฌ ๐จ๐ซ ๐ซ๐จ๐ญ๐๐ฆ๐๐ซ๐ฌ")`
Alkanes can thus have infinite number of conformations by rotation around `color{red}(C-C)` single bonds. However, rotation around a `color{red}(C-C)` single bond is not completely free but it is hindered by a small energy barrier of `color{red}(1- 20 kJ mol^(โ1))` due to weak repulsive interaction between the adjacent bonds. Such a type of repulsive interaction is called torsional strain.
`color{green}("๐๐จ๐ง๐๐จ๐ซ๐ฆ๐๐ญ๐ข๐จ๐ง๐ฌ ๐จ๐ ๐๐ญ๐ก๐๐ง๐ :")` Ethane molecule `color{red}((C_2H_6))` contains a carbon โ carbon single bond with each carbon atom attached to three hydrogen atoms. Considering the ball and stick model of ethane, keep one carbon atom stationary and rotate the other carbon atom around the `color{red}(C-C)` axis. This rotation results into infinite number of spatial arrangements of hydrogen atoms attached to one carbon atom with respect to the hydrogenatoms attached to the other carbon atom. These are called conformational isomers (conformers). Thus there are infinite number of conformations of ethane. However, there are two extreme cases:
โข One such conformation in which hydrogen atoms attached to two carbons are as closed together as possible is called eclipsed conformation
โขThe other in which hydrogens are as far apart as possible is known as the staggered conformation.
โข Any other intermediate conformation is called a skew conformation.
In all the conformations, the bond angles and the bond lengths remain the same. Eclipsed and the
staggered conformations can be represented by Sawhorse and Newman projections.
`color{green}("๐. ๐๐๐ฐ๐ก๐จ๐ซ๐ฌ๐ ๐ฉ๐ซ๐จ๐ฃ๐๐๐ญ๐ข๐จ๐ง๐ฌ")`
In this projection, the molecule is viewed along the molecular axis. It is then projected on paper by drawing the central CโC bond as a somewhat longer straight line. Upper end of the line is slightly tilted towards right or left hand side. The front carbon is shown at the lower end of the line, whereas the rear carbon is shown at the upper end. Each carbon has three lines attached to it corresponding to three hydrogen atoms. The lines are inclined at an angle of `color{red}("120ยฐ")` to each other. Sawhorse projections of eclipsed and staggered conformations of ethane are depicted in Fig. 13.2.
`color{green}("๐. ๐๐๐ฐ๐ฆ๐๐ง ๐ฉ๐ซ๐จ๐ฃ๐๐๐ญ๐ข๐จ๐ง๐ฌ")`
In this projection, the molecule is viewed at the `color{red}(CโC)` bond head on. The carbon atom nearer to the eye is represented by a point. Three hydrogen atoms attached to the front carbon atom are shown by three lines drawn at an angle of `color{red}("120ยฐ")` to each other. The rear carbon atom (the carbon atom away from the eye) is represented by a circle and the three hydrogen atoms are shown attached to it by the shorter lines drawn at an angle of `color{red}("120ยฐ")` to each other. The Newmanโs projections are depicted in Fig. 13.3.
Free rotation about `color{red}(CโC)` single bond is possible because of symmetric electron distribution of the sigma molecular orbital around the internuclear axis of the `color{red}(CโC)` bond which is not disturbed due to rotation about its axis. This rotation results into different spatial arrangements of atoms in space which can change into one another.
`color{green}("๐๐ฎ๐๐ก ๐ฌ๐ฉ๐๐ญ๐ข๐๐ฅ ๐๐ซ๐ซ๐๐ง๐ ๐๐ฆ๐๐ง๐ญ๐ฌ ๐จ๐ ๐๐ญ๐จ๐ฆ๐ฌ ๐ฐ๐ก๐ข๐๐ก ๐๐๐ง ๐๐ ๐๐จ๐ง๐ฏ๐๐ซ๐ญ๐๐ ๐ข๐ง๐ญ๐จ")` `color{green}("๐จ๐ง๐ ๐๐ง๐จ๐ญ๐ก๐๐ซ ๐๐ฒ ๐ซ๐จ๐ญ๐๐ญ๐ข๐จ๐ง ๐๐ซ๐จ๐ฎ๐ง๐ ๐ ")` `color{green}("๐-๐ ๐ฌ๐ข๐ง๐ ๐ฅ๐ ๐๐จ๐ง๐ ๐๐ซ๐ ๐๐๐ฅ๐ฅ๐๐ ๐๐จ๐ง๐๐จ๐ซ๐ฆ๐๐ญ๐ข๐จ๐ง๐ฌ ๐จ๐ซ ๐๐จ๐ง๐๐จ๐ซ๐ฆ๐๐ซ๐ฌ ๐จ๐ซ ๐ซ๐จ๐ญ๐๐ฆ๐๐ซ๐ฌ")`
Alkanes can thus have infinite number of conformations by rotation around `color{red}(C-C)` single bonds. However, rotation around a `color{red}(C-C)` single bond is not completely free but it is hindered by a small energy barrier of `color{red}(1- 20 kJ mol^(โ1))` due to weak repulsive interaction between the adjacent bonds. Such a type of repulsive interaction is called torsional strain.
`color{green}("๐๐จ๐ง๐๐จ๐ซ๐ฆ๐๐ญ๐ข๐จ๐ง๐ฌ ๐จ๐ ๐๐ญ๐ก๐๐ง๐ :")` Ethane molecule `color{red}((C_2H_6))` contains a carbon โ carbon single bond with each carbon atom attached to three hydrogen atoms. Considering the ball and stick model of ethane, keep one carbon atom stationary and rotate the other carbon atom around the `color{red}(C-C)` axis. This rotation results into infinite number of spatial arrangements of hydrogen atoms attached to one carbon atom with respect to the hydrogenatoms attached to the other carbon atom. These are called conformational isomers (conformers). Thus there are infinite number of conformations of ethane. However, there are two extreme cases:
โข One such conformation in which hydrogen atoms attached to two carbons are as closed together as possible is called eclipsed conformation
โขThe other in which hydrogens are as far apart as possible is known as the staggered conformation.
โข Any other intermediate conformation is called a skew conformation.
In all the conformations, the bond angles and the bond lengths remain the same. Eclipsed and the
staggered conformations can be represented by Sawhorse and Newman projections.
`color{green}("๐. ๐๐๐ฐ๐ก๐จ๐ซ๐ฌ๐ ๐ฉ๐ซ๐จ๐ฃ๐๐๐ญ๐ข๐จ๐ง๐ฌ")`
In this projection, the molecule is viewed along the molecular axis. It is then projected on paper by drawing the central CโC bond as a somewhat longer straight line. Upper end of the line is slightly tilted towards right or left hand side. The front carbon is shown at the lower end of the line, whereas the rear carbon is shown at the upper end. Each carbon has three lines attached to it corresponding to three hydrogen atoms. The lines are inclined at an angle of `color{red}("120ยฐ")` to each other. Sawhorse projections of eclipsed and staggered conformations of ethane are depicted in Fig. 13.2.
`color{green}("๐. ๐๐๐ฐ๐ฆ๐๐ง ๐ฉ๐ซ๐จ๐ฃ๐๐๐ญ๐ข๐จ๐ง๐ฌ")`
In this projection, the molecule is viewed at the `color{red}(CโC)` bond head on. The carbon atom nearer to the eye is represented by a point. Three hydrogen atoms attached to the front carbon atom are shown by three lines drawn at an angle of `color{red}("120ยฐ")` to each other. The rear carbon atom (the carbon atom away from the eye) is represented by a circle and the three hydrogen atoms are shown attached to it by the shorter lines drawn at an angle of `color{red}("120ยฐ")` to each other. The Newmanโs projections are depicted in Fig. 13.3.