3SAS #31-38 p.235

31.  A) Propane, C3H8
       B) Pentane, C5H12

32. The suffix -ane indicates that hexane is an alkane.

33. Yes, each of these molecules are isomers of each other. They all consist of 5 carbon atoms and 12 hydrogen atoms. They appear to be different because of the arrangement of atoms. These three molecules are structured isomers of one another, due to the fact that they have identical molecular formulas, but different arrangements of atoms.

34.

35. Butane (C4H10) is the shortest-chain alkane that can demonstrate isomerism- alkanes with four or more carbon atoms can be demonstrated as straight-chain structures, branched-chain structures, and ring structures.

36. Both representations are correct because their different arrangements of atoms do not change the identical molecular formulas of the molecule; this would make the molecules structural isomers of each other.

37. A) 

B) The branched-chain molecule would have the lower boiling point. Since the straight-chain molecule has greater molecule-to-molecule contact, it has a stronger intermolecular force than the branched-chain molecule, resulting in a higher boiling point.

38. A) A short, straight chain would have a lower boiling point because of decreased molecule-to-molecule contact than the longer boiling point. The bonds of this chain would be easier to break than a longer straight chain.

       B) A short, branched chain would have the lower boiling point. Although the bonds of a branched chain are easier to break than those of a straight chain, it would be more difficult to break more molecular bonds within the long chain, resulting in a higher boiling point.

       C) A short, branched chain would have a lower boiling point. Straight chains have stronger intermolecular forces that hold together each molecule in contact; where as bonds between branched chains are more breakable due to the decreased intermolecular molecular forces between them.