Write a structural formula for the most stable conformation of each of the following compounds:
(a) 2, 2, 5, 5-Tetramethylhexane (Newman projection of conformation about C-3—C-4 bond)
(b) 2, 2, 5, 5-Tetramethylhexane (zigzag conformation of entire molecule)
(c) cis-1-Isopropyl-3-methylcyclohexane
(d) trans-1-Isopropyl-3-methylcyclohexane
(e) cis-1-tert-Butyl-4-ethylcyclohexane
(f) cis-1, 1, 3, 4-Tetramethylcyclohexane