Question

Which statement is true for cyclohexane

(A) It has two possible isomers
(B) It has three conformations
(C) Boat conformation is most stable
(D) Chair and boat conformations differ in energy by 44 kJ/mol

Answer 1

Isomers are compounds with the same molecular formula but different chemical structure. This property of compounds exhibiting isomers is called isomerism. For the isomers, it is not necessary that they will share the same physical properties or chemical properties.

Complete Step by step solution:
There are two main types of isomers which are structural isomers and stereoisomers. The structural isomers are also known as constitutional isomers whereas the stereoisomers are also known as spatial isomers.
Structural isomers or constitutional isomers of a molecule are other molecules which have the same number of atoms of each element but the bonds which are present are different.
Stereoisomers are the isomers with the same molecular formula and bonds but differ in their three-dimensional arrangement. In stereoisomerism, conformational isomerism is a form in which just due to rotations isomers can be obtained. Rotation of the compound takes place through a single bond. The two isomers obtained by rotation of a single bond are called conformers of each other. There can be infinite conformers for a compound. While rotating, the isomers have to overcome the rotational energy barrier to interconvert into one another.
Cyclohexane has a non - polar structure that makes it free from strain. The most important conformation cyclohexane can have boat conformation and chair conformation. The chair conformation is more stable than boat conformation. Chair conformation of cyclohexane is more stable than boat because in chair it has C-H bonds that are equatorial and axial that are six axial C-H bonds and six equilateral C-H bonds. Each carbon atom has one axial and one equilateral C-H bond.
The chair being more stable than the boat, there is an energy difference between the chair and the boat conformations of cyclohexane which is 44 kJ/mol.
Therefore, the true statement is option D.

Note:
Isomers are formed as every compound wants to achieve stability, this can be through resonance or rotational of bonds or changing of positions of atoms. Among the structural isomers they have further subtypes as follows:
ring chain isomers
tautomers
chain isomers
position isomers
metamers
functional isomers.