Rank the following according to boiling point, highest to lowest: a. CH 3 CH 2 CH 2 OH b. CH 3 CH 2 (OH)CH 2 OH c. CH 3 CH 2 CH 3 d. CH 2 (OH)CH(OH)CH 2 OH

Hi everybody. Let's look at our next problem. Arrange the following. In order of increasing boiling point, we have four different molecules. And then our choices A through D are these four molecules in different order. So let's look at each one of those after thinking about what affects boiling point. So boiling point is affected by how strong the intermolecular forces are between molecules. The stronger the IMF the higher the boiling point as it takes more energy put in to make the molecule spread apart in a gas. So what are the different IMF forces which are the strongest ones, the strongest, of course are ion dipole interactions? And then after that hydrogen bonds after that dipole dipole interactions and the lowest of all are dispersion forces. Shall let's look at each of these and we see that we have all of them have alcohol groups, different numbers of them and different length chains. So what are the factors in these structures that will affect boiling point? Well, length of carbon chain will affect that because the longer the chain, the greater the surface area. And so that means more chance or more of these dispersion forces since wherever that most molecules will interact. Well, you'll see these dispersion forces acting as temporary tiny little attractions. So a longer chain will have a higher boiling point, high BP. And then the number of O groups will affect boiling point because the oh groups are capable of hydrogen bonding. So the greater the number, the higher the boiling point now, which of these is a bigger factor. Well, that will be the alcohol groups. And that's because those um hydrogen bonds are stronger IMF s than the dispersion forces. So we'll put an asterisk by a number of oh groups since that's the more significant. So when we look at our molecules to try and order them, we see that we have a 12345 carbon chain with two hydroxy groups on the chain. And then a hydroxy group branched off. So that would be three hydroxy groups on a molecule with six carbons molecule. For molecule one or molecule two, we just have methanol. So one carbon. So one carbon 10 for number three, we have 123 carbons and 20 groups. And then for molecule number four, we have two carbons and 20 groups. So we know that our molecule number one, which has three hydroxy groups will have the highest boiling point, more hydroxy groups than anything else. So we would expect that to be last. So number one should be our last option since that will have the highest boiling point. Well, only choice C has number one as the last option. So we can eliminate, just by looking at that, we can eliminate A B and D. So A has number one listed. First. B has it listed second and D has it listed third. But we'd like to be a little more thorough going through everything. But again, just remember on a test, you wouldn't have to go any further. So that's our highest boiling point. Next, we would look at our two molecules that have two hydroxy groups. So that's three and four. So now we look at the length of the carbon chain. Well, molecule three has three carbons, while molecule four has two carbons, so the longer chain would have the higher boiling point. So molecule three will be the next highest. So it should be third in the list and then molecule four should be second. And we see that in choice C that is indeed the case. And then finally, molecule two with just one hydroxy group and one carbon would be our lowest boiling point. So this corresponds with what we see in choice C. So choice C will be our answer. In order of increasing boiling point, we have 243 and then one. So choice C is that correct answer? See you in the next video.

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14. Compounds with Oxygen or Sulfur

Naming Alcohols

GOB Chemistry

14. Compounds with Oxygen or Sulfur

Naming Alcohols

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Problem 6

Textbook Question

Rank the following according to boiling point, highest to lowest:
a. CH₃CH₂CH₂OH
b. CH₃CH₂(OH)CH₂OH
c. CH₃CH₂CH₃
d. CH₂(OH)CH(OH)CH₂OH

Verified step by step guidance

Step 1: Understand that boiling point is influenced by intermolecular forces. The stronger the intermolecular forces, the higher the boiling point. Key forces to consider are hydrogen bonding, dipole-dipole interactions, and London dispersion forces.

Step 2: Analyze the molecular structures of the compounds. Identify the presence of functional groups like hydroxyl (-OH) groups, which can form hydrogen bonds, significantly increasing boiling points.

Step 3: Compare the number of hydroxyl (-OH) groups in each compound: (a) CH₃CH₂CH₂OH has one -OH group, (b) CH₃CH₂(OH)CH₂OH has two -OH groups, (c) CH₃CH₂CH₃ has no -OH groups, and (d) CH₂(OH)CH(OH)CH₂OH has three -OH groups.

Step 4: Rank the compounds based on the number of hydrogen bonds they can form. Compound (d) with three -OH groups will have the highest boiling point, followed by (b) with two -OH groups, then (a) with one -OH group, and finally (c) with no -OH groups, which relies only on weaker London dispersion forces.

Step 5: Final ranking from highest to lowest boiling point is: (d) CH₂(OH)CH(OH)CH₂OH > (b) CH₃CH₂(OH)CH₂OH > (a) CH₃CH₂CH₂OH > (c) CH₃CH₂CH₃.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Boiling Point and Intermolecular Forces

The boiling point of a substance is influenced by the strength of its intermolecular forces. Stronger forces, such as hydrogen bonding, lead to higher boiling points. Alcohols, which can form hydrogen bonds due to their hydroxyl (-OH) groups, typically have higher boiling points than hydrocarbons, which primarily exhibit weaker van der Waals forces.

Hydroxyl Groups and Alcohols

Alcohols are organic compounds characterized by the presence of one or more hydroxyl (-OH) groups. The number and arrangement of these groups significantly affect the boiling point. For instance, more hydroxyl groups generally increase the potential for hydrogen bonding, thus raising the boiling point compared to hydrocarbons with no hydroxyl groups.

Structural Isomerism

Structural isomerism occurs when compounds have the same molecular formula but different structural arrangements. This can affect physical properties like boiling point. In the given compounds, variations in the position and number of hydroxyl groups lead to different boiling points, highlighting the importance of molecular structure in determining these properties.

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