Editing Hydrogen (section)

===Protons and acids ===
{{Further|Acid–base reaction}}
[[File:Base pair AT.svg|282px|thumb|right| An "A-T base pair" in DNA illustrating how hydrogen bonds are critical to the [[genetic code]].  The drawing illustrates that in many chemical depictions, C-H bonds are not always shown explicitly, an indication of their pervasiveness.]]
In water, hydrogen bonding plays an important role in reaction thermodynamics. A hydrogen bond can shift over to proton transfer.
Under the [[Brønsted–Lowry acid–base theory]], acids are proton donors, while bases are proton acceptors.<ref>{{Cite book |last=Punekar |first=Narayan S. |url=https://link.springer.com/10.1007/978-981-97-8179-9_28 |title=ENZYMES: Catalysis, Kinetics and Mechanisms |date=2025 |publisher=Springer Nature Singapore |isbn=978-981-97-8178-2 |location=Singapore |pages=333–345 |language=en |doi=10.1007/978-981-97-8179-9_28}}</ref>{{rp|loc=28}}
A bare proton, {{chem2|H+}} essentially cannot exist in anything other than a vacuum. Otherwise it attaches to other atoms, ions, or molecules.  Even species as inert as methane can be protonated. The term 'proton' is used loosely and metaphorically to refer to refer to solvated {{chem2|H+}}" without any implication that any single protons exist freely as a species.  To avoid the implication of the naked proton in solution, acidic aqueous solutions are sometimes considered to contain the "[[hydronium]] ion" ({{chem2|[H3O]+}}) or still more accurately, {{chem2|[H9O4]+}}.<ref name="Okumura">{{cite journal
|last1=Okumura|first1=A. M.
|last2=Yeh|first2=L. I.|last3=Myers|first3=J. D.|last4=Lee|first4=Y. T.
|title=Infrared spectra of the solvated hydronium ion: vibrational predissociation spectroscopy of mass-selected H<sub>3</sub>O+•(H<sub>2</sub>O<sub>)n</sub>•(H<sub>2</sub>)<sub>m</sub>
|journal=Journal of Physical Chemistry
|date=1990|volume=94|issue=9|pages=3416–3427|doi=10.1021/j100372a014
}}</ref> Other [[oxonium ion]]s are found when water is in acidic solution with other solvents.<ref name="Perdoncin">{{cite journal
|last1=Perdoncin|first1=G.|last2=Scorrano|first2=G.
|title=Protonation Equilibria in Water at Several Temperatures of Alcohols, Ethers, Acetone, Dimethyl Sulfide, and Dimethyl Sulfoxide
|journal=Journal of the American Chemical Society
|date=1977|volume=99|issue=21|pages=6983–6986
|doi=10.1021/ja00463a035
|bibcode=1977JAChS..99.6983P }}</ref>

The concentration of these solvated protons determines the [[pH]] of a solution, a [[logarithmic scale]] that reflects its acidity or basicity. Lower pH values indicate higher concentrations of hydronium ions, corresponding to more acidic conditions.<ref name="housecroft" />