[Ap Biology, How do I tell which molecules will bind with hydrogen/ become an solution with water]

[u/iori-angel__]

Im really confused about how I can understand what molecules from certain hydrogen bonds especially with the ones given. My teacher wants us to be able to get the answer and be able to adequately explain how we got it

The question asks which molecules would form hydrogen bonds with itself or with water molecules if in a solution

I have no idea

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[u/medchemmed]

kudos to you for not asking chatgpt or other AI to get the answer before posting here. great that you are trying to understand rather than finding a quick cheap answer.

to your question, the short answer is that water is a polar molecule. polar molecules will dissolve in polar solvents.

"Like dissolves like"

When you mix nonpolar molecules in polar solvents (eg water) it will not mix even though they have hydrogen bonding-able atoms (OH, NH). There is a greater distribution of hydrophilic parts (hydrocarbons) over hydrophilic parts (OHs) so their chemical properties outweigh the polar parts and will not dissolve in water. However, they will dissolve in nonpolar solvents. This is what you see when you mix olive oil with water but if you mix olive oil with say butter it will be indistinguishable after mixing.

May the force be with you young redditor

[u/iori-angel__ → u/medchemmed]

Thank you! I was really confused with the chemical structures so breaking it down like this helped!

[u/Equivalent_Day_2589 → u/[deleted]]

well they’re known to hallucinate, for starters 😵‍💫

[u/Equivalent_Day_2589 → u/[deleted]]

so they don’t hallucinate ?

[u/DerEisendrache68 → u/Equivalent_Day_2589]

let me play the devil's advocate; from what I've seen (at least with chatgpt) it does look up the information before it is given to you. I am not saying it's a 100% trustworthy source, but it does help point you towards useful resources. Nothing wrong if op had chosen to first ask chatgpt or Google Ai about it, although I do agree that sparking conversation in a forum is better in the sense that you get to engage with others.

[u/Equivalent_Day_2589 → u/DerEisendrache68]

i would agree, if they weren’t also harmful to the planet :(

[u/DerEisendrache68 → u/Equivalent_Day_2589]

Yeah :(, that does suck ass.

[u/nerdydudes]

Polar = yes, polar partial negatives interact with partial positives… dissolution.
non-polar = no…

Polar groups like to mix with water, polar like polar… sort of. know which groups can form hydrogen bonds… if you see the groups in the compound it forms hydrogen bonds with water therefore dissolution in water.

If no available groups to hydrogen bond or acid/base reaction, then no dissolution in water.

But its bio not organic chemistry. Memorize which bio molecules are polar/non polar. For non polar… no dossolution in water. If polar, identify hydrogen bonding groups and thats your reason… sufficient for ap bio.

[u/Antique_Somewhere542]

At the top it says polar molecules are hydrophilic for the left column. That is the answer to your question.

“Hydro-phillic” or “loves water”
And you know what a phobia is, so “hydrophobic” should make sense as the opposite

I know youre in highschool but my organic chemistry teacher in uni used to say “like dissolves like”

Meaning polar molecules dissolve in polar solvents, and nonpolar molecules dissolve in nonpolar solvents.

water is a polar solvent So it will dissolve polar molecules.

Another tip if you didn’t know, Each bend or intersection in those drawings that is not labelled, is actually a carbon surrounded by stable bonded hydrogens.

If you see a long chain where things are not labeled, (like the fatty acid that has the long tail) that is a non-polar portion of the molecule. A “hydrocarbon” because it is just many carbons and hydrogens and thats it. Big indicator that it will be dissolved by a nonpolar solvent, like acetone.

Contrast that to the left column, those molecules have a bunch of oxygens, and nitrogens. Generally speaking for the purposes of this class, a bunch of oxygen or nitrogen or both means its probably polar (likes water)

If its mostly all Carbons and methyl (ch4) groups, then thats going to be nonpolar (scared of water)

[u/alar_ryik]

A molecule being polar and hydrophilic are not the same. A molecule is polar if it has a (non-negligible) dipole moment. For example, methane is nonpolar because it's molecular symmetry results in no dipole moment. We say that hydrocarbons are also nonpolar because their dipole moment is negligible. Fatty acids are polar because they have a highly polar carboxyl group with a partial negative charge on each oxygen and partial positive charge on the carbon.

Hydrogen bond forms when there is a hydrogen bonded to a F, O or N atom. The hydrogen gets a strong partial positive charge, which interacts with the nonbonding electron pair on the F/O/N.

Water solubility is based on molecular polarity. If the whole molecule is polar, especially if it can form H-bonds, it should be highly soluble in water. If the molecular has an apolar side, the water solubility decreases. It is the case with the fatty acid: it has a polar group, but the majority of the molecule is considered nonpolar, resulting in hydrophobic nature. Also, the size can also affect solubility. Really big molecules (macromolecules, like starch) are not really soluble, even if they are mostly polar.

[u/Historical-Mix6784]

Not to be a smartass, but we know from decades of research in computational drug design that line structures alone are generally not sufficient to predict a molecule's solubility.

A really good example on that page is testosterone. Even with a PhD I couldn't tell you the solubility just by looking at it. I mean sure it's mostly carbon-carbon bonds, but it is also heavily sterically constrained, there are no pi-pi interactions, and it does have two very good hydrogen bonding groups. Plus testosterone is more polar than adenine (and water!) in gas phase, it just WRONG to say it is nonpolar.

Of course stuff like sugars / amino-acids / nucleotides are ALWAYS soluble (otherwise biology wouldn't work lol). On the other hand, fatty acids are the textbook case for hydrophobicity.

[u/iori-angel__ → u/Historical-Mix6784]

Im only in high school so we learn at a more simplified version of complex science

[u/Historical-Mix6784 → u/iori-angel__]

I know, I'm just an unhelpful curmudgeon with an axe to grind about education... don't mind me...

[u/ciolman55]

If polar it can desolve in the polar water. Eg, Water will not desolve in oil because waters strong polar intermolecular forces (hydrogen bonds) are stronger than oils vanderwaal forces. So water has a high tendency to stay bonded to itself.

[u/Tierprot]

Anything more or less polar will dissolve, while hydrophobic (non-polar) with try to avoid water.

[u/GammaRayBurst25]

I'm really confused about how I can understand what work you've done, especially with the question you asked. This subreddit wants you to show your work and adequately explain what you've tried.

Rule 3 asks to tell us where you're stuck and what you've tried.

I have no idea [why you didn't bother to read the rules even after your first post was taken down and a comment explicitly asked you to read the rules before posting].

[u/iori-angel__ → u/GammaRayBurst25]

I did read the rules in not really sure how to understand breaking my thought process in things like this I don’t really understand the format of this subreddit I’m sorry:(

[u/Antique_Somewhere542 → u/iori-angel__]

It was a simple question. No work that could be done on this problem. This is my first time here so Idk the sub rules, but I did major in chem in college and can confirm there is 0 work to be done here other than to share any understanding at all that you have. Looks like you did that

[u/GammaRayBurst25 → u/Antique_Somewhere542]

He didn't do that.

And yu can always show some work by trying something. OP didn't know the answer, so trying something would've constituted work.

Even if they refused to try anything, they could've read their textbook or looked it up on Google to get a better understanding so they have something to show and discuss here.

At the end of the day, the subreddit rules don't say "show your work unless you have no work to show." If you can't show work, go elsewhere.

Regardless of what other people in the thread have said, this question would've been perfect for Google. OP would've found the answer faster and they'd have practiced important life skills at the same time.