Sir, please help me to answer this question with reasoning.
Which of the ,
cyclopropane, cyclobutane, cyclopentane do not exixt as confirmers...

Hi Bharath,

Cyclopropane, Cyclobutane cannot exist as conformers.

Cyclopropane can exist only in a planar configuration, with C-C-C angle of 60 deg.

Whereas Cyclobutane has a distorted puckered configuration, to reduce the torsional strain

But Cyclopentane will have two conformers, the envelope structure and the twist structure.

These structures need to be committed to memory. NCERT gives a very good explanation on bonding in Organic Compounds.

All the best.

Regards,

Ashwin (IIT Madras).