Question 11.2: Do the structural formulas in each of the following sets rep...
Do the structural formulas in each of the following sets represent the same compound or constitutional isomers? (Hint: You will find it helpful to redraw each molecule as a line-angle formula, which will make it easier for you to see similarities and differences in molecular structure.)
Strategy
First, find the longest chain of carbon atoms. It makes no difference whether the chain is drawn as straight or bent; as structural formulas are drawn in this problem, there is no attempt to show three-dimensional shapes. Second, number the longest chain from the end nearest the first branch. Third, compare the lengths of the two chains and the sizes and locations of any branches. Structural formulas that have the same molecular
formula and the same connectivity of their atoms represent the same compound; those that have the same molecular formula but different connectivities of their atoms represent constitutional isomers.
(a) Each structural formula has an unbranched chain of six carbons;
they are identical and represent the same compound.
(b) Each structural formula has the same molecular formula, C_7H_{16}. In addition, each has a chain of five carbons with two CH_3 branches. Although the branches are identical, they are at different locations on the chains. Therefore, these structural formulas represent constitutional isomers.
