Is H base a neutral molecule? Or is it slightly electronegative (due to the amine)?

RedHat

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Heroin in its base form (Heroin No.3) is hydrophobic, which means it's insoluble in water. This is because the molecule is neutral, meaning it has no charge. Water on the other hand is a polar molecule, meaning it has positive and negative parts on it. Before the heroin can dissolve in water, it needs to have a charge that will give it the ability to attract to the charged parts on the water molecules.
This can be done with the help of an acid such as citric or ascorbic acid, which are also polar molecules. When the acid is added into water, it disassociates, which means the hydrogen atoms leave the acid molecule without their electrons (H+) and become hydrogen ions, otherwise known as protons (hence why this process is called protonation). The protons are attracted to the nitrogen atom on the heroin molecules, and when it joins, it gives the heroin molecule a slightly positive charge, which then means its attracted to the parts of the water molecules that are negatively charged.

Some of that is explained in this YouTube video.

The part that I'm a little confused about is how the proton is attracted to the nitrogen atom. Protons are attracted to molecules with negative parts, and this is what makes them a "base". And that seems to make sense, especially since the heroin in this stage is referred to as heroin base. But if it had a negative charge, then one would think that it would be attracted to the positively charged parts of the water molecules.

I know that the heroin molecule has an amine group in it (which is the nitrogen and the three hydrogens attached to it). And according to this, Because the amine has a pair of unbonded electrons, it can attract a hydrogen ion (proton) to it. Does this mean that because the molecule has an amine group, it IS a base? And if its a base with a slightly negative charge, why won't it dissolve in water by bonding to the electropositive parts of the water molecules? Or is the heroin molecule overall a neutral charge, but the nitrogen atom itself is basic? (that seems to be the likely answer)
 

S.J.P.

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Heroin in its base form (Heroin No.3) is hydrophobic, which means it's insoluble in water. This is because the molecule is neutral, meaning it has no charge.
A molecule does not necessarily have to be charged to be water soluble ("hydrophilic"). It just has to be relatively polar. Glucose, for example, is a highly water-soluble, neutral molecule.

Water on the other hand is a polar molecule, meaning it has positive and negative parts on it.
It's important to make a distinction between polar molecules like water, where electron density in the molecule is distributed unevenly but the molecule is neutral, and charged species, like ammonium salts, where there is a full positive and a full negative charge on different parts of the molecule.

The protons are attracted to the nitrogen atom on the heroin molecules, and when it joins, it gives the heroin molecule a slightly positive charge...
It in fact gives the heroin molecule a full positive charge, which is balanced out by the negative charge on the portion of the acid from which the proton was removed.

For example, when you add HCl (hydrochloric acid) to heroin (R3N) you end up with [R3NH]+ and Cl-.

The part that I'm a little confused about is how the proton is attracted to the nitrogen atom. Protons are attracted to molecules with negative parts, and this is what makes them a "base". And that seems to make sense, especially since the heroin in this stage is referred to as heroin base. But if it had a negative charge, then one would think that it would be attracted to the positively charged parts of the water molecules.

I know that the heroin molecule has an amine group in it (which is the nitrogen and the three hydrogens attached to it). And according to this, Because the amine has a pair of unbonded electrons, it can attract a hydrogen ion (proton) to it. Does this mean that because the molecule has an amine group, it IS a base? And if its a base with a slightly negative charge, why won't it dissolve in water by bonding to the electropositive parts of the water molecules? Or is the heroin molecule overall a neutral charge, but the nitrogen atom itself is basic? (that seems to be the likely answer)
Amines have a lone pair of electrons and have a relatively high propensity to have this pair of electrons attack a proton (H+). When the amine lone pair attacks the proton, the positive charge is transferred to the nitrogen. This propensity to attack protons makes amines - and the molecules they are attached to, including heroin - basic. It is true that amines will interact with the electropositive portion of water. This occurs through what is called a hydrogen bond: the amine lone pair interacts with the electropositive hydrogens of water. Because of this, amines can be quite water soluble. If you took ammonia or methylamine freebase, both would be highly soluble in water. However, you have to consider the entirety of the molecule when determining whether it will dissolve well in water or not. Heroin has one amine, and two esters, which are fairly polar groups, but most of the molecule is made up of highly non-polar carbon-carbon and carbon-hydrogen bonds. It is this latter property that makes molecules hydrophobic. In the case of heroin, the hydrocarbon skeleton dominates over the sparse polar functionality in determining the overall polarity of the molecule. When you acidify an amine, however, you put a full positive and full negative charge onto the molecule. This drastically increases the polarity and will make most amines of reasonable size water soluble.
 

atara

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It's about the geometry. Consider an electric dipole consisting of a large cloud of positive charge next to a small ball of negative charge. This dipole may be "neutral", but it will interact more strongly with positive ions than negative ions, because the negative charge is more localized.

Similarly, neutral amines have a concentration of negative charge on the lone pair of the nitrogen atom, with the corresponding positive charge shielded by the bonding orbitals.
 

Hodor

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When the acid is added into water, it disassociates, which means the hydrogen atoms leave the acid molecule without their electrons (H+) and become hydrogen ions, otherwise known as protons (hence why this process is called protonation).
This sentence is worded really strangely. Just so we're on the same page:
Let's say we take acetic acid, commonly shortened to "HAc" in chemistry speak, and dump it in water.
It will indeed dissociate, following the reaction HAc -> H+ + Ac-
HAc, as we've established, is acetic acid. H+ is a positively charged hydrogen ion which is the same as a proton. H+ is not the same as an electron, which is called "e-" (I apologize if I misread your post), although in an acid-base reaction, you just write it as a "-" charge next to the negatively charged species. In this case, the negative species is "Ac-", commonly referred to as the "acetate ion"; Ac- is the so-called "conjugate base" of acetic acid.

"Protonation" is the act of adding a proton to a base. For example, if the proton attaches to one of the acetate ions (which are, after all, a base), this would be protonation (H+ + Ac- -> HAc).
Or in the case of heroin's amine group, NR3 + H+ -> NR3H+ (the "R" stands for an "alkyl chain", i.e. a chain of carbon atoms).

I know that the heroin molecule has an amine group in it (which is the nitrogen and the three hydrogens attached to it). And according to this, Because the amine has a pair of unbonded electrons, it can attract a hydrogen ion (proton) to it. Does this mean that because the molecule has an amine group, it IS a base? And if its a base with a slightly negative charge, why won't it dissolve in water by bonding to the electropositive parts of the water molecules? Or is the heroin molecule overall a neutral charge, but the nitrogen atom itself is basic? (that seems to be the likely answer)
Ammonia (NH3) does not carry an overall negative charge, yet is both polar and a base. Why is this so? Because the electron density is not evenly distributed across the molecule. As you can plainly see below, NH3's lone pair (which is facing away from the hydrogen atoms) causes the electron density to be much higher on one side of the molecule than the other. So the electron-poor hydrogen atoms in, say, water can interact with the electron-dense lone pair in ammonia, and vice versa for the hydrogen atoms in ammonia and the two electron pairs on the oxygen atom. Compare this to methane (CH4), which is symmetrical in its electron density and thus non-polar.


So why aren't all amines water-soluble? Because remember, heroin is much more than its amine group. Most of the bonds in the molecule are between carbon and hydrogen or carbon and carbon. These structures make the molecule much *less* water soluble. Indeed, I previously wrote the amine in heroin freebase as "NR3", which means that the nitrogen isn't even directly connected to a single hydrogen, and that instead all of its bonds are to carbon. So while it retains the increased electron density on the nitrogen, it doesn't have hydrogen atoms of its own that could directly interact with the lone pairs of the water molecule - very much unlike ammonia.

One thing to keep in mind about chemistry is that there generally aren't any absolutes.
Take, for example, methanol, CH3OH. It is sort of like methane in that it has a CH3 group, but also like water in that is has an OH group. So in terms of solubility, it is polar enough to be readily miscible with water, but also capable of dissolving some compounds that would be too non-polar to dissolve in water. Adding another carbon atom we get ethanol, C2H5OH, which is also fully miscible with water, but generally better at dissolving non-polar stuff, and worse at dissolving water-soluble salts.
So how about 2 more carbon atoms? We get butanol, C4H9OH. Despite having the OH-group contributing a degree of polarity, its behavior as a solvent is dominated by the chain of carbon atoms, meaning its solubility in water is greatly reduced, while being better able to dissolve organic compounds.
So you see, a compound can be both hydrophilic (polar) and lipophilic (non-polar) to some extent.
 
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LucidSDreamr

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another simple way to look at the reason heroin base is not water soluble is but cause it has such a great amount of hydrophobic groups (basically everything in the molecule that is carbon and not N or O).

The more hydrocarbon in the molecule the harder it will be to dissolve it in water. this is overridden by addition in the charge during protonation of the N, which gives the compound enough polarity to then disssolve. Ethanol for example, while it has hydrocarbon, this hydrocarbon portion of the molecule is so small relative to the polar portion of the molecule (the side with OH) that ethanol is still able to dissolve in water even though it doesn't have a charge.
 

RedHat

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Wow! So many replies with amazing details! Will take some time to go through each and reply. Thanks for taking the time out of your day to help me out!
 
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