Q.A) Differentiate between configurational and conformational isomers.
B) The chair conformer of cyclohexane is more stable than boat conformer. Explain.

Configurational isomers are distinct, isolable compounds that differ in fixed 3-D arrangement, while conformational isomers are the same molecule in different, freely interconvertible shapes produced by rotation about single bonds; cyclohexane's chair form beats its boat form because it avoids both torsional and steric strain.

A) Configurational vs conformational isomers:

Configurational isomers (stereoisomers in the strict sense) differ in the fixed, three-dimensional arrangement of atoms/groups around a stereocentre or a double bond. They are genuinely different, separable/isolable compounds, because converting one into another requires breaking and re-forming covalent bonds. Examples: cis-trans (geometrical) isomers, and R/S (optical) enantiomers.

Conformational isomers (conformers) are different momentary spatial arrangements of the SAME molecule that arise purely from rotation about carbon-carbon (or other) single (sigma) bonds. They interconvert freely and rapidly at room temperature (low rotational energy barrier) without breaking any bond, and generally cannot be isolated as separate, stable compounds. Examples: staggered and eclipsed forms of ethane; chair and boat forms of cyclohexane.

B) Chair conformer more stable than boat conformer:

In the chair conformation of cyclohexane, every pair of adjacent C-C bonds is perfectly staggered when viewed along any C-C bond (Newman projection), so there is zero torsional (eclipsing) strain; all C-C-C bond angles are close to the ideal tetrahedral value of 109.5 degrees, so there is minimal angle strain; and the ring geometry keeps all atoms well separated, so there is no significant steric clash.

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