Editing Pyridine (section)

===Spectroscopy===
The optical [[Absorption Spectrum|absorption spectrum]] of pyridine in [[hexane]] consists of bands at the [[wavelength]]s of 195, 251, and 270&nbsp;nm.  With respective extinction coefficients (''ε'') of 7500, 2000, and 450&nbsp;L·mol<sup>−1</sup>·cm<sup>−1</sup>, these bands are assigned to π&nbsp;→&nbsp;π*, π&nbsp;→&nbsp;π*, and n&nbsp;→&nbsp;π*  transitions. The compound displays very low [[fluorescence]].<ref>{{cite journal |last1=Varras |first1=Panayiotis C. |last2=Gritzapis |first2=Panagiotis S. |last3=Fylaktakidou |first3=Konstantina C. |title=An explanation of the very low fluorescence and phosphorescence in pyridine: a CASSCF/CASMP2 study |journal=Molecular Physics |date=17 January 2018 |volume=116 |issue=2 |pages=154–170 |doi=10.1080/00268976.2017.1371800|url=https://figshare.com/articles/journal_contribution/5414566 }}</ref>

The <sup>1</sup>H [[nuclear magnetic resonance]] (NMR) spectrum shows signals for α-([[chemical shift|δ]] 8.5), γ-(δ7.5) and β-protons (δ7). By contrast, the proton signal for benzene is found at δ7.27. The larger chemical shifts of the α- and γ-protons in comparison to benzene result from the lower electron density in the α- and γ-positions, which can be derived from the resonance structures. The situation is rather similar for the [[13C NMR|<sup>13</sup>C&nbsp;NMR]] spectra of pyridine and benzene: pyridine shows a triplet at ''δ''(α-C)&nbsp;=&nbsp;150&nbsp;ppm, δ(β-C)&nbsp;=&nbsp;124&nbsp;ppm and δ(γ-C)&nbsp;=&nbsp;136&nbsp;ppm, whereas benzene has a single line at 129&nbsp;ppm. All shifts are quoted for the solvent-free substances.<ref>[[#Joule|Joule]], p.&nbsp;16</ref> Pyridine is conventionally detected by the [[gas chromatography]] and [[mass spectrometry]] methods.<ref name=osha>{{cite book |url=http://monographs.iarc.fr/ENG/Monographs/vol77/mono77-21.pdf |title=Pyridine |work=IARC Monographs 77 |publisher=OSHA |location=Washington DC |date=1985 |access-date=7 January 2011 |archive-date=4 March 2016 |archive-url=https://web.archive.org/web/20160304083832/http://monographs.iarc.fr/ENG/Monographs/vol77/mono77-21.pdf |url-status=live }}</ref>