There are four dimethylcyclopropane isomers.
(a) Write three-dimensional formulas for these isomers.
(b) Which of the isomers are chiral?
(c) If a mixture consisting of 1 mol of each of these isomers were subjected to simple gas chromatography (an analytical method that can separate compounds according to boiling point), how many fractions would be obtained and which compounds would each fraction contain?
(d) How many of these fractions would be optically active?