29. Draw each of the following substituted cyclobutanes in its two interconverting "puckered" conformations (Figure 4-3). When the two conformations differ in energy, identify the more stable shape and indicate the form(s) of strain that raise the relative energy of the less stable one. (Hint: Puckered cyclobutane has axial and equatorial positions similar to those in chair cyclohexane.) (a) Methylcyclobutane (b) cis-1,2-Dimethylcyclobutane (c) trans-1,2-Dimethylcyclobutane (d) cis-1,3-Dimethylcyclobutane (e) trans-1,3-Dimethylcyclobutane Which is more stable: cis- or trans-1,2-dimethylcyclobutane; cis- or trans-1,3-dimethylcyclobutane?