Editing Hydrogen peroxide (section)

===Structure===
<div class="skin-invert-image">
{{multiple image
| direction = hoizontal
| align = left
| header =
| width = 210
| image1 = H2O2 gas structure.svg
| alt1 = O−O bond length = 147.4 pm<br/>O−H bond length = 95.0 pm
| caption1 = Structure and dimensions of {{chem2|H2O2}} in the gas phase
| image2 = H2O2 solid structure.svg
| alt2 = O−O bond length = 145.8 pm<br/>O−H bond length = 98.8 pm
| caption2 = Structure and dimensions of {{chem2|H2O2}} in the solid (crystalline) phase
}}</div>

Hydrogen peroxide ({{chem2|H2O2}}) is a nonplanar molecule with (twisted) C<sub>2</sub> [[Molecular symmetry#Common point groups|symmetry]]; this was first shown by [[Paul-Antoine Giguère]] in 1950 using [[infrared spectroscopy]].<ref>{{cite journal |vauthors = Giguère PA |date=1950 |title=The Infra-Red Spectrum of Hydrogen Peroxide |journal=Journal of Chemical Physics |volume=18 |issue=1 |page=88 |doi=10.1063/1.1747464 |url=https://authors.library.caltech.edu/11457/1/GIGjcp50.pdf |access-date=31 December 2018 |archive-url=https://web.archive.org/web/20171202122026/https://authors.library.caltech.edu/11457/1/GIGjcp50.pdf |archive-date=2 December 2017 |url-status=live |bibcode=1950JChPh..18...88G}}</ref><ref>{{cite journal |vauthors = Giguère PA |date=1983 |title=Molecular association and structure of hydrogen peroxide |journal=[[Journal of Chemical Education]] |volume=60 |issue=5 |pages=399–401 |doi=10.1021/ed060p399 |bibcode=1983JChEd..60..399G}}</ref> Although the O−O bond is a [[single bond]], the molecule has a relatively high [[rotational barrier]] of 386&nbsp;[[inverse centimeter|cm<sup>−1</sup>]] (4.62&nbsp;[[Kilojoule|kJ]]/[[Mole (chemistry)|mol]]) for rotation between [[enantiomer]]s via the [[Cis–trans isomerism|''trans'']] configuration, and 2460&nbsp;cm<sup>−1</sup> (29.4&nbsp;kJ/mol) via the [[Cis–trans isomerism|''cis'']] configuration.<ref name="Hunt1965">{{cite journal |vauthors = Hunt RH, Leacock RA, Peters CW, Hecht KT |date=1965 |title=Internal-Rotation in Hydrogen Peroxide: The Far-Infrared Spectrum and the Determination of the Hindering Potential |journal=The Journal of Chemical Physics |bibcode=1965JChPh..42.1931H |doi=10.1063/1.1696228 |volume=42 |issue=6 |page=1931 |url=https://deepblue.lib.umich.edu/bitstream/handle/2027.42/71115/JCPSA6-42-6-1931-1.pdf?sequence=2 |hdl=2027.42/71115 |access-date=9 April 2014 |archive-url=https://web.archive.org/web/20140409085232/https://deepblue.lib.umich.edu/bitstream/handle/2027.42/71115/JCPSA6-42-6-1931-1.pdf?sequence=2 |archive-date=9 April 2014 |url-status=live |hdl-access=free}}</ref> These barriers are proposed to be due to [[Repulsion (chemistry)|repulsion]] between the [[lone pair]]s of the adjacent oxygen atoms and dipolar effects between the two O–H bonds. For comparison, the rotational barrier for [[ethane]] is 1040&nbsp;cm<sup>−1</sup> (12.4&nbsp;kJ/mol).

The approximately 100° [[dihedral angle]] between the two O–H bonds makes the molecule [[chiral]]. It is the smallest and simplest molecule to exhibit [[enantiomer]]ism. It has been proposed that the [[stereospecific|enantiospecific]] interactions of one rather than the other may have led to amplification of one enantiomeric form of [[ribonucleic acid]]s and therefore an origin of [[homochirality]] in an [[RNA world]].<ref>{{cite journal |vauthors = Ball R, Brindley J |title = The Life Story of Hydrogen Peroxide III: Chirality and Physical Effects at the Dawn of Life |journal = Origins of Life and Evolution of the Biosphere |volume = 46 |issue = 1 |pages = 81–93 |date = March 2016 |pmid = 26399407 |doi = 10.1007/s11084-015-9465-y |s2cid = 9564774 |bibcode = 2016OLEB...46...81B}}</ref>

The molecular structures of gaseous and [[crystalline]] {{chem2|H2O2}} are significantly different. This difference is attributed to the effects of [[hydrogen bonding]], which is absent in the gaseous state.<ref>{{cite book |vauthors = Dougherty DA, Anslyn EV |date=2005 |title=Modern Physical Organic Chemistry |publisher=University Science |isbn=978-1-891389-31-3 |page=122}}</ref> Crystals of {{chem2|H2O2}} are [[tetragonal]] with the [[space group]] ''D''{{su|b=4|p=4}} or ''P''4<sub>1</sub>2<sub>1</sub>2.<ref>{{cite journal |vauthors = Abrahams SC, Collin RL, Lipscomb WN |date=1 January 1951|title=The crystal structure of hydrogen peroxide |journal=Acta Crystallographica |doi=10.1107/S0365110X51000039 |volume=4 |issue=1 |pages=15–20|bibcode=1951AcCry...4...15A |doi-access=free}}</ref>