Without referring to a table, place the following hydrocarbons in order of increasing boiling points. (a) methane (d) neopentane (b) n-hexane (e) 2,3 -dimethylbutane (c) n-undecane

First, write down the chemical formula for each hydrocarbon mentioned in the exercise: (a) Methane: CH4 (b) n-Hexane: C6H14 (c) n-Undecane: C11H24 (d) Neopentane: C5H12 (e) 2,3-Dimethylbutane: C6H14

When comparing the boiling points of hydrocarbons, we must consider the size of the molecules. Larger molecules have more electrons and therefore exhibit stronger London dispersion forces (LDFs). Since LDFs are the primary factors determining boiling points in hydrocarbons, larger molecules will generally have higher boiling points.

The presence of branching in hydrocarbon molecules can also affect their boiling points. Branched molecules have a more compact shape, which reduces their surface area and thus weakens their LDFs. Consequently, branched hydrocarbons usually have lower boiling points than their linear counterparts.

Based on the structural features mentioned above, let's organize the hydrocarbons in the given exercise according to their size and degree of branching: 1. Methane (CH4) - the smallest molecule, without branching. 2. Neopentane (C5H12) - a small molecule with 4 branches. 3. 2,3-Dimethylbutane (C6H14) - a medium-sized molecule with 2 branches. 4. n-Hexane (C6H14) - a medium-sized, unbranched molecule. 5. n-Undecane (C11H24) - the largest, unbranched molecule.

Keeping in mind that larger molecules and those with less branching will have higher boiling points, we can now place the hydrocarbons in order of increasing boiling points: 1. Methane (CH4) - the smallest molecule, with the lowest boiling point. 2. Neopentane (C5H12) - a small molecule with higher boiling point than methane, but lower than other unbranched or less branched longer hydrocarbons. 3. 2,3-Dimethylbutane (C6H14) - a medium-sized molecule with lower boiling point than unbranched hexane due to having more branching. 4. n-Hexane (C6H14) - an unbranched, medium-sized molecule with a higher boiling point due to less branching and greater size than the previous hydrocarbons. 5. n-Undecane (C11H24) - the largest and unbranched molecule, with the highest boiling point. So, the order of increasing boiling points is: methane < neopentane < 2,3-dimethylbutane < n-hexane < n-undecane.