Predict the water solubility of each of the following organic molecules:

Name: Problem 41, Chapter 3: Organic Chemistry
Uploaded: 2019-08-17T17:44:13-08:00
Duration: 3 min 23 s
Channel: Ian Kaigh
Description: Predict the water solubility of each of the following organic molecules:

Predict the water solubility of each of the following...

Key Concepts

Solvent-Solute Interactions and the 'Like Dissolves Like' Principle

The 'like dissolves like' principle emphasizes that substances with similar types of intermolecular forces tend to dissolve each other. In practical terms, polar solvents like water are better at dissolving polar substances, while non-polar solvents are better for non-polar substances. This concept helps in understanding and predicting the interactions between water and various organic molecules, ultimately guiding the analysis of solubility.

Functional Groups

Functional groups are specific groups of atoms within molecules that dictate chemical behavior and properties, including solubility. For instance, groups like hydroxyl (-OH), amino (-NH2), and carboxyl (-COOH) are polar and can form hydrogen bonds with water, thereby enhancing solubility. Recognizing the types and positions of these groups in an organic molecule is key to predicting its solubility in water.

Hydrophobic/Hydrophilic Balance

The hydrophobic/hydrophilic, or lipophilic/hydrophilic balance, describes the proportion of water-repelling versus water-attracting parts of a molecule. Even if a molecule contains polar functional groups, a large non-polar, hydrophobic region can hinder its overall solubility in water. This balance is essential for predicting how well a molecule will interact with the polar solvent environment of water.

Molecular Polarity

Molecular polarity refers to the distribution of electrical charge across a molecule. In the context of water solubility, polar molecules are more likely to dissolve in water because water is a polar solvent. This concept is essential for predicting solubility, as molecules with significant differences in electronegativity across bonds create regions of partial positive and negative charge that interact favorably with water molecules.

Hydrogen Bonding

Hydrogen bonding is a type of strong dipole-dipole interaction where a hydrogen atom covalently bonded to an electronegative atom such as oxygen or nitrogen interacts with another electronegative atom. This phenomenon is crucial for water solubility because functional groups capable of hydrogen bonding significantly enhance a molecule's interaction with water, thereby increasing its solubility.

Transcript

00:01 This is the answer to chapter three, problem number 41 from the smith organic chemistry textbook.

00:09 And in this problem, we're given four fairly complex molecules, and we're asked to predict the water solubility of each.

00:19 And so in order to do that, remember this rule that the book suggests that i've written up the top of the screen here, which is for every five carbons in a molecule.

00:31 It needs to have one polar functional group capable of hydrogen bonding in order to be water soluble.

00:40 So looking at a, we can see right off the bat that 1, 2, 3, 4, 5, 6, 7.

00:48 There are 7 carbons in this molecule and 1, 2, 3, 4, 5, 6 polar functional groups.

00:56 So this molecule is very polar and it is water soluble.

01:02 So that's caffeine, by the way.

01:06 So looking at this steroid molecule that we have for b, so we can see that there's an ether here, the och3.

01:18 So this is an ether.

01:19 This is obviously an alcohol.

01:22 And that's it.

01:23 Two polar functional groups that could h bond and many more than 10 carbons.

01:31 We have three, six -membered rings and a five -membered ring, and then some branches and stuff.

01:38 So, you know, well over 10 carbons.

01:42 And so the answer to b is going to be not water -soluble.

01:50 Because remember, in order to be water -soluble, it needs to have one polar functional group per five carbons.

01:57 And that's not the case in b...

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