Hydrogen donor compounds lose their hydrogen and participate in chemical reactions. Hydrogen-bond donors are involved in weak non-chemical bond interactions and are important in binding, influencing the pKa of compounds, interacting with active sites, etc.

Prof. Andrei

Thank you so much

is there any specific hydrogen involved in the chemical reaction or just random ?

For the hydrogen bonding only the one attached to electronegative atom

A hydrogen bond forming between a hydrogen donor (has H, H will not leave unless in the case of exchanging of H) and an atom has electron pair (N or O), this atom with electron pair is hydrogen bond donor, I think. A strong acid will give out H , it will be ionic . Weak acid with H will serve as H donor for forming H bond.

H2O can be both H donor and hydrogen bond donor (O), -NH2 in H donor, N in =N- is hydrogen bond donor.

Dr. Guobing

Thank you so much that made everything clear

Mohammad,

you are welcome!

Hydrogen bond donors are electronegative atoms (typically F, N, or O, but other atoms can participate) that "donate" hydrogen in a non-covalent way--to another electronegative atom (again, typically F, N, or O). In this diagram X---H -- A, if we establish that H is bonded to the X atom, it's a hydrogen bond donor; A is the hydrogen bond acceptor.

Hydrogen donors donate (i.e., give their hydrogen and its constituent electrons) to another atom.

In conclusion, hydrogen bond donation has no "bonding" in the sense that you know of, where electrons from a hydrogen are transferred from one atom to the next for a significant amount of time to create a new bond. It's an electrostatic association.

Joey

Thanks for sharing

Do you know what elements only donate their hydrogens and what makes an atom share its hydrogen in H2 bonding rather than losing it all when it has a lone pair and can sustain its stability

Sorry for the late response, but it depends on the chemical environment. Let's say you have an atom within a molecule that's especially acidic, and it's close enough in proximity to an atom that's basic. By convention, the definition of "acidic," is a species that gives up a hydrogen relatively easily. What makes this process move forward depends on a lot of things: solvent, strength of base, atom that the hydrogen is connected to, atom that the aforementioned hydrogen-connected atom is connected to, etc. And all of these points are underscored by thermodynamic and quantum effects that are too involved to get into here.

As far as what makes an atom hydrogen bond as opposed to engage in an acid-base reaction, again, the scope of this is too vast to discuss here, as the same thermodynamic and quantum effects are involved. Down to brass tacks, the energetics of whatever happens (whether it's an acid-base reaction or just an electrostatic association) happen to be favored in that particular case.

Hydrogen bonds are formed between a hydrogen atom bound to a small, highly electronegative atom and another small, highly electronegative atom with an unshared electron pair. The elements that usually participate in hydrogen bonds are nitrogen, oxygen, and fluorine. A hydrogen bond is much weaker than a covalent bond (10-40 kJ/mol vs. hundreds of kJ/mol for a covalent bond), but when a lot of hydrogen bonds are added together, they can have a significant influence on the structure of molecules. An example of hydrogen bonding is the lattice formed by water molecules in ice. In biological molecules, the electronegative atoms the hydrogen atom is "shared" by are usually oxygen and nitrogen.

Scientists distinguish between the electronegative atoms in a hydrogen bond based on which atom the hydrogen atom is covalently bonded to. In the diagram at left below, the oxygen atom of the hydroxy group is called the hydrogen bond donor, because it is "donating" its hydrogen to the nitrogen. The nitrogen atom is called the hydrogen bond acceptor, because it is "accepting" the hydrogen from the oxygen. In the picture of two water molecules at lower right, the oxygen of the water molecule B is the hydrogen bond donor. The oxygen of water molecule A is the hydrogen bond acceptor.

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