Conformation of butane is :
Conformation of butane is :
The correct option is C
Conformations of butane: As the alkane molecule becomes larger, the conformation situation becomes more complex. In butane CH3−CH2−CH2−CH3, for example, the rotation about the single bond between two inner atoms C2andC3 is considered. In this case, all the staggered as well as eclipsed conformations will not have same stability and energy because of different types of interaction between C - C (of methyl) and C - H bonds.
The lowest energy conformation will be the one, in which the two methyl groups are as far apart as possible i.e., 180∘ away form each other.
This conformation will be maximum staggered and is called anti conformation (marked I). Other conformations can be obtained by rotating one of the C2orC3 carbon atoms through an angle of 60∘ as shown ahead.
As is clear from the above Newman projection the Gauche or Skew conformations (III and V) are also staggered. However, in these conformations, the methyl groups are so close that they repel each other. This repulsion causes gauche conformations, to have about 3.8 kJ mol-1 more energy than anti conformation. The conformations II and VI are eclipsed conformations. These are unstable because of repulsions. These are 16 kJ mol-1 less stable than anti conformation. Conformation IV is also eclipsed and it is least stable having energy 19 kJ mol-1 more than anti conformation. This is because of repulsion between methyl-methyl groups which are very closed together. It is called fully eclipsed conformation.
The order of stability of these conformations is, Anti > Skew or Gauche > Eclipsed >Fully eclipsed.
Conformations of butane: As the alkane molecule becomes larger, the conformation situation becomes more complex. In butane CH3−CH2−CH2−CH3, for example, the rotation about the single bond between two inner atoms C2andC3 is considered. In this case, all the staggered as well as eclipsed conformations will not have same stability and energy because of different types of interaction between C - C (of methyl) and C - H bonds.
The lowest energy conformation will be the one, in which the two methyl groups are as far apart as possible i.e., 180∘ away form each other.
This conformation will be maximum staggered and is called anti conformation (marked I). Other conformations can be obtained by rotating one of the C2orC3 carbon atoms through an angle of 60∘ as shown ahead.
As is clear from the above Newman projection the Gauche or Skew conformations (III and V) are also staggered. However, in these conformations, the methyl groups are so close that they repel each other. This repulsion causes gauche conformations, to have about 3.8 kJ mol-1 more energy than anti conformation. The conformations II and VI are eclipsed conformations. These are unstable because of repulsions. These are 16 kJ mol-1 less stable than anti conformation. Conformation IV is also eclipsed and it is least stable having energy 19 kJ mol-1 more than anti conformation. This is because of repulsion between methyl-methyl groups which are very closed together. It is called fully eclipsed conformation.
The order of stability of these conformations is, Anti > Skew or Gauche > Eclipsed >Fully eclipsed.