Question

Substituted cyclobutadiene derivatives with bulky alkyl groups are easier to isolate instead of unsubstituted cyclobutadiene derivatives. Do you find any reason behind

Answer 1

All cyclobutadiene derivatives possess high tendency to polymerization. Due to steric hindrance, bulky substituents (especially tert-butyl) at the cyclobutadiene ring make the molecule much more less polymerizable. Therefore, you can isolate it much easier. However, The contact with air should be avoided even for substituted cyclobutadiene.

More information you can find here: https://doi.org/10.1002/anie.197805201