Editing Infrared spectroscopy (section)

==Absorption bands==
IR spectroscopy is often used to identify structures because [[functional group]]s give rise to characteristic bands both in terms of intensity and position (frequency). The positions of these bands are summarized in correlation tables as shown below.
{{Main|Infrared spectroscopy correlation table}}
[[File:IR-spectroscopy-sample.svg|thumb|800px|center|List of main IR spectroscopy bands. For example, the carboxyl group will contain a C = O band at 1700 cm<sup>−1</sup> and an OH band at 3500 cm<sup>−1</sup> (total group -COOH). Wavenumbers listed in [[wavenumber|cm<sup>−1</sup>]].]]

===Regions===
A spectrograph is often interpreted as having two regions.<ref name=OChemSmith3E>{{cite book | last1 = Smith | first1 = Janice Gorzynski | editor1-last = Hodge | editor1-first = Tami | editor2-last = Nemmers | editor2-first = Donna | editor3-last = Klein | editor3-first = Jayne | name-list-style = vanc | title = Organic chemistry | date = 2011 | publisher = McGraw-Hill | location = New York, NY | isbn = 978-0-07-337562-5 | pages = 463–488 | edition = 3rd | chapter-url = http://highered.mheducation.com/sites/007340277x/student_view0/index.html | chapter-format = Book | chapter = Chapter 13 Mass Spectrometry and Infrared Spectroscopy | access-date = 2018-06-30 | archive-date = 2018-06-28 | archive-url = https://web.archive.org/web/20180628152511/http://highered.mheducation.com/sites/007340277x/student_view0/index.html | url-status = dead }}</ref>
* '''functional group region''' <math>\geq 1,500 \text{ cm}^{-1}</math>
In the functional region there are one to a few troughs per functional group.<ref name=OChemSmith3E />
* '''fingerprint region''' <math> < 1,500 \text{ cm}^{-1}</math>
In the fingerprint region there are many troughs which form an intricate pattern which can be used like a fingerprint to determine the compound.<ref name=OChemSmith3E />

===Badger's rule===
For many kinds of samples, the assignments are known, i.e. which bond deformation(s) are associated with which frequency. In such cases further information can be gleaned about the strength on a bond, relying on the empirical guideline called '''Badger's rule'''. Originally published by [[Richard McLean Badger]] in 1934,<ref>{{cite journal| vauthors = Badger R |title=A Relation Between Internuclear Distances and Bond Force Constants|journal= The Journal of Chemical Physics |date=1934 |volume=2 |issue=3 |page=128 |doi=10.1063/1.1749433 |bibcode=1934JChPh...2..128B|url=https://authors.library.caltech.edu/10440/1/BADjcp34.pdf}}</ref> this rule states that the strength of a bond (in terms of force constant) correlates with the bond length. That is, increase in bond strength leads to corresponding bond shortening and vice versa.