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Vazba uhlík–fluor: Porovnání verzí

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[[Soubor:Carbon-fluorine-bond-polarity-2D-black.png|thumb|Částečné náboje polarizované vazby uhlík–fluor]]
 
'''Vazba uhlík–fluor''' je [[kovalentní vazba]] mezi atomy [[uhlík]]u a [[fluor]]u, obsažená v  all [[organofluoridy|organických sloučeninách fluoru]]. Jedná se o jednu z nejsilnějších chemických vazeb - po [[jednoduchá vazba|jednoduchých vazbách]] B-F , Si-F a H-F; navíc je poměrně krátká, protože má částečně vlastnosti [[iontová vazba|iontové vazby]]. Vazba je silnější, pokud je na stejný uhlík navázáno více atomů fluoru. [[fluorované uhlovodíky|Fluoroalkany]], jako je [[tetrafluormethan]] tak patří k nejméně reaktivním organickým sloučeninám.
 
== Elektronegativita a energie vazeb ==
<!-- The highVysoká [[electronegativityelektronegativita]] of fluorinefluoru (4.,0 for fluorine vs.oproti 2.,5 foru carbonuhlíku) givesdodává thevazbě carbon–fluorineuhlík-fluor bond a significantznačnou [[Chemicalpolární polaritymolekula|polaritypolaritu]]/[[Electron electrica dipolevelký moment|dipole[[dipólový moment]]. The[[Elektronová electronhustota|Elektronová densityhustota]] isje concentratedsoustředěna aroundkoolem thefluoru fluorine,a leavinguhlík theje tak carbonpoměrně relativelychudý electronna poorelektrony. ThisVzniklé introducesčástečné ionic character to the bond through [[partial charges]]náboje (C<sup>δ+</sup>&mdash;F<sup>δ&minus;</sup>). Thedodávají partialvazbě chargesčástečně oniontovou thepovahu fluorinea androvněž carbonzpůsobují arenebvyklou attractive,sílu contributing to the unusual bond strength of the carbon–fluorine bondvazby. TheTatao bondvazba isbývá labeledoznačována asjako "the„Nejsilnější strongestv&nbsp;organické in organic chemistrychemii“,"<ref name=hagan>{{cite journal |author=D. O'Hagan D |title=Understanding organofluorine chemistry. An introduction to the C–F bond |journal=Chem Soc Rev |volume=37 |issue=2 |pages=308–19 |date=February 2008 |pmid=18197347 |doi=10.1039/b711844a }}</ref> becauseprotože fluorinefluor formsvytváří thenejsilnější strongestjednoduchou singlevazbu bond to carbons&nbsp;uhlíkem. Carbon–fluorineVazby bondsuhlík-fluor canmohou have amít [[bonddisociační dissociationenergie energyvazby|disociační energie]] (BDE)až ofokolo up to 130 kcal540&nbsp;kJ/mol.<ref name="Lemal2004">Lemal DM. [https://www.ncbi.nlm.nih.gov/pubmed/14703372 "Perspective on Fluorocarbon Chemistry"] J Org Chem. 2004, volume 69, p 1–11. {{doi|10.1021/jo0302556}}</ref> TheDisociační BDEenergie (strengthC-F ofjsou thevyšší bond)než ofu C-Fjakýchkoliv isjiných highervazeb than other carbon–uhlík-[[halogeny|halogen]] anda carbon–uhlík–[[hydrogenvodík]] bonds. For example, thenapříklad BDEsu of thevazby C-X bond within av&nbsp;molekule CH<sub>3</sub>-X moleculeje ispostupně 115482, 104.9439, 83.7350, 72.1,302 anda 57.6 kcal241&nbsp;kJ/mol forpro X = fluorinefluor, [[hydrogen]]vodík, [[chlorinechlor]], [[brominebrom]], anda [[iodinejod]], respectively.<ref name=blanksby>{{cite journal | vauthors=S. J. Blanksby SJ, EllisonG. GBB. Ellison |title=Bond dissociation energies of organic molecules |journal=Acc.[[Accounts Chem.of Res.Chemical Research]] |volume=36 |issue=4 |pages=255–63 |date=April 2003 | pmid = 12693923 | doi = 10.1021/ar020230d |citeseerx=10.1.1.616.3043 }}</ref>
 
== BondDélka lengthvazby ==
Délky vazeb C-F bývají obvykle kolem 135&nbsp;pm (139&nbsp;pm u [[fluormethan]]u).<ref name=hagan/> Jsou kratší než ostatní vazby uhlík–halogen a také kratší než jednoduché vazby [[vazba uhlík-dusík|uhlík-dusík]] a [[vazba uhlík–kyslík|uhlík–kyslík]], i&nbsp;když má fluor větší [[relativní atomová hmotnost|relativní atomovou hmotnost]]. Malá délka vazeb je způsobována její částečně iontovou povahou a z&nbsp;ní vyplývaícího elektrostatického přitahování částečných nábojů na uhlíku a fluoru. V&nbsp;závislosti na typu [[hybridizace orbitalů|hybridizace]] uhlíkového atomu a přítomnosti dalších substituentů na uhlíku, nebo i vzdálenějších atomech, se její délka může lišit o několik [[[Metr#Pikometr|pm]]. Tyto změny mohou být vyvolávány změnami v&nbsp;hybridizaci a [[elektronové efekty|prostorovými elektronovými interakcemi]]. V&nbsp;tabulce níže jsou znázorněny různé délky vazeb C-F u různých molekul (atomy uhlíku mají hybridizaci sp<sup>3</sup>, pokud není uvedeno jinak).
The carbon–fluorine bond length is typically about 1.35 [[ångström]] (1.39 Å in [[fluoromethane]]).<ref name=hagan/> It is shorter than any other carbon–halogen bond, and shorter than single carbon–[[nitrogen]] and carbon–[[oxygen]] bonds, despite fluorine having a larger [[atomic mass]]. The short length of the bond can also be attributed to the ionic character/electrostatic attractions between the partial charges on carbon and fluorine. The carbon–fluorine bond length varies by several hundredths of an ångstrom depending on the hybridization of the carbon atom and the presence of other substituents on the carbon or even in atoms farther away. These fluctuations can be used as indication of subtle hybridization changes and [[stereoelectronic interaction]]s. The table below shows how the average bond length varies in different bonding environments (carbon atoms are sp<sup>3</sup>-hybridized unless otherwise indicated for sp<sup>2</sup> or aromatic carbon).
 
:{| class="wikitable"
|-
! BondVazba !! Mean bondPrůměrná lengthdélka (Åpm)<ref>F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G. Orpen. Tables of bond Lengths determined by X-Ray and Neutron Diffraction. Part 1. Bond Lengths in Organic Compounds. [[Perkin Transactions|''J. Chem. Soc. Perkin Trans. II'']] '''1987''', S1-S19.</ref>
|-
| CCH<sub>2</sub>F, C<sub>2</sub>CHF || 1.399139,9
|-
| C<sub>3</sub>CF || 1.428142,8
|-
| C<sub>2</sub>CF<sub>2</sub>, H<sub>2</sub>CF<sub>2</sub>, CCHF<sub>2</sub> || 1.349134,9
|-
| CCF<sub>3</sub> || 1.346134,6
|-
| FCNO<sub>2</sub> || 1.320132,0
|-
| FCCF || 137,1.371
|-
| C<sub>sp2</sub>F || 1.340134,0
|-
| C<sub>ar</sub>F || 1.363136,3
|-
| FC<sub>ar</sub>C<sub>ar</sub>F || 1.340134,0
|}
 
TheRozílné variabilitydélky invazeb bonda lengthsjejich andzkracování thev&nbsp;důsledku shorteningčástečně ofiontových bondsvlastností tobylo fluorinetaké duepozorováno tou theirvazeb partialfluoru ionics&nbsp;jinými character are also observed for bonds between fluorine and other elements, and have beenprvky a sourcestalo ofse difficultieszdrojem withpotíží thepři selection of an appropriate value for theurčování [[covalentkovalentní radius ofpoloměr|kovalentního fluorinepoloměru]] fluoru. [[Linus Pauling]] originallypůvodně suggesteduvedl hodnotu 64 [[picometer|&nbsp;pm]], butkterá thatvšak valuebyla waspoté eventuallyupravena replaced byna 72 &nbsp;pm, whichcož isje halfpolovina ofdélky thevazby fluorine–fluorineF–F, bondje length.to However,však 72příliš pmmnoho, isaby toomohlo longjít too bereprezentativní representativehodnotu ofpro thevazby lengthsfluoru ofs&nbsp;jinými theprvky, bondsa betweentak fluorinebyly andjinými otherautory elements,navrženy so values betweendélky 54 &nbsp;pm anda 60 &nbsp;pm have been suggested by other authors.<ref>{{cite journal | authorauthor1 = Ronald Gillespie Ronald | author2 = Robinson Edward Robinson | year = 1992 | title = Bond Lengths in Covalent Fluorides. A New Value for the Covalent Radius of Fluorine | journal = Inorganic Chemistry | volume = 31 | issue = 10 | pages = 1960–1963 | doi=10.1021/ic00036a045}}</ref><ref>{{cite journal | author = Robinson Edward Robinson | author2 = Samuel Johnson Samuel | author3 = Tang Ting-Hua | author4 = Ronald Gillespie Ronald | year = 1997 | title = Reinterpretation of the Lengths of Bonds to Fluorine in Terms of an Almost Ionic Model | journal = Inorganic Chemistry | volume = 36 | issue = 14| pages = 3022–3030 | doi=10.1021/ic961315b | pmid=11669953}}</ref><ref>{{cite journal | author = Cordero Beatriz Cordero | author2 = Gómez Verónica Gómez | author3 = Platero-Prats Ana E. Platero-Prats | author4 = Revés Marc Revés | author5 = Echeverría Jorge Echeverría | author6 = Cremades Eduard Cremades | author7 = Barragán Flavia Barragán | author8 = Alvarez Santiago | s2cid = 244110Alvarez | year = 2008 | title = Covalent radii revisited | journal = [[Dalton TransTransactions]] | volume = 2008 | issue = 21 | pages = 2832–2838 | doi = 10.1039/b801115j | pmid = 18478144 }}</ref><ref>{{cite journal | author = Pyykkö P. Pyykkö | author2 = Atsumi M. Atsumi | year = 2009 | title = Molecular Single-Bond Covalent Radii for Elements 1-118| journal=Chemistry: A European Journal| volume = 15 | issue = 1| pages = 186–197 | doi = 10.1002/chem.200800987 | pmid = 19058281 }}</ref>
 
== Síly geminálních vazeb==
==Bond strength effect of geminal bonds==
S&nbsp;rostoucím počtu atomů fluoru navázaných na stejný ([[geminální]]) uhlík se zvyšují energie a snižují délky ostatních vazeb, což je vidět například u fluorovaných derivátů methanu, jak je zobrazeno níže v&nbsp;tabulce;mění se také částečné náboje (''q''<sub>C</sub> a ''q''<sub>F</sub>) na atomech.<ref name="Lemal2004"/> Částečný kladný náboj na uhlíku při přidávání dalších fluorů zesiluje, čímž se zvýrazňují elektrostatické působení i iontovost vazby mezi atomy fluoru a uhlíku.
With increasing number of fluorine atoms on the same ([[geminal]]) carbon the other bonds become stronger and shorter. This can be seen by the changes in bond length and strength (BDE) for the fluoromethane series, as shown on the table below; also, the [[partial charges]] (''q''<sub>C</sub> and ''q''<sub>F</sub>) on the atoms change within the series.<ref name="Lemal2004"/> The partial charge on carbon becomes more positive as fluorines are added, increasing the electrostatic interactions, and ionic character, between the fluorines and carbon.
 
:{| class="wikitable"
|-
!Sloučenina
!Compound
!Délka vazby C-F bond length (Åpm)
!BDEDisociační energie (kcalkJ/mol)
!''q''<sub>C</sub>
!''q''<sub>F</sub>
|-
|CH<sub>3</sub>F
|138,5
|1.385
|109.9460 ± 14
|0.,01
| −0.,23
|-
|CH<sub>2</sub>F<sub>2</sub>
|135,7
|1.357
|500
|119.5
|0.,40
| −0.,23
|-
|CHF<sub>3</sub>
|133,2
|1.332
|534
|127.5
|0.,56
| −0.,21
|-
|CF<sub>4</sub>
|131,9
|1.319
|130.5546 ± 313
|0.,72
| −0.,18
|}
 
== Gauche effectSpektroskopie ==
TheV&nbsp;[[infračervená carbon–fluorinespektroskopie|infračerveném bondspektru]] stretchinglze appearspozorovat innatahování thevazeb [[infraredC-F spectrum]] betweenmezi 1000 anda 1360&nbsp;cm<sup>−1</sup>. TheRozmezí wideje rangeširoké, isprotože duefrekvence toje theovlivňována sensitivityostatními ofsubstituenty the stretching frequency to other substituents in the moleculev&nbsp;molekule. MonofluorinatedMonofluorované compoundssločeniny havemají aširoký strongbás band betweenmezi 1000 anda 1110&nbsp;cm<sup>−1</sup>; withjestliže moreje thanpřítomen onevíce fluorinenež atoms, the band splits intojeden twoatom bandsfluoru, onetak forse thepás symmetricrozdělí modena and one for the asymmetricdva.<ref>{{cite book |title=Infrared and Raman characteristic group frequencies: tables and charts | author = George Socrates |author2=Socrates |publisher=John Wiley and Sons |year=2001 |isbn=978-0-470-09307-8 |pages=198}}</ref> TheC-F carbon–fluorinepásy bandsjsou arenatolik so strong that they may obscure anyvýrazné, carbon–hydrogenže bandsmohou thatpřekonat mightpřípadné beC–H presentpásy.<ref>{{cite book |title=Infrared Spectroscopy: Fundamentals and Applications |author=Barbara H. Stuart |publisher=John Wiley and Sons |year=2004 |isbn=978-0-470-85428-0 |pages=82}}</ref>▼
 
[[Organofluorine compoundsOrganofluoridy]] canlze alsotaké bezkoumat characterized usingpomocí [[NMRspektroskopie spectroscopynukleární magnetické rezonance]], usings&nbsp;využitím [[carbonuhlík-13|uhlíku-13]], [[fluorinefluor-19|fluoru-19]] nebo (thepokud onlyje natural fluorine isotopepřítomen), or [[hydrogenprotium|vodíku-1]] (if present). The [[chemicalChemický shiftposun|Chemické posuny]]s inpři [[fluorine19-19 NMR|<sup>19</sup>F NMR]] appearse, overv&nbsp;závislosti ana verymíře widesubstituce range,a dependingdruhu onnavázaných thefunkčních degreeskupin ofvyskytují substitutionve andvelmi functionalširokém grouprozmezí. TheV&nbsp;tabulce tableníže belowjsou showsuvedena therozmezí rangespro fornejběžnější someskupiny of the major classessloučenin.<ref>{{cite web|url=http://nmr.chem.indiana.edu/NMRguide/misc/19Fshifts.html |title=Archived copy |accessdate=2008-11-09 |url-status=dead |archive-url=https://web.archive.org/web/20080515131118/http://nmr.chem.indiana.edu/NMRguide/misc/19Fshifts.html |archive-date=2008-05-15 }}</ref>▼
[[Image:GaucheEffect.png|250px|thumb|right|Anti (left) and gauche (right) conformations of 1,2-difluoroethane. The second row shows the [[Newman projection]].]] When two fluorine atoms are in [[vicinal (chemistry)|vicinal]] (i.e., adjacent) carbons, as in [[1,2-difluoroethane]] (H<sub>2</sub>FCCFH<sub>2</sub>), the [[gauche (chemistry)|gauche]] conformer is more stable than the anti conformer—this is the opposite of what would normally be expected and to what is observed for most 1,2-disubstituted ethanes; this phenomenon is known as the ''[[gauche effect]]''.<ref name=Craig>''Contribution to the Study of the Gauche Effect. The Complete Structure of the Anti Rotamer of 1,2-Difluoroethane'' Norman C. Craig, Anthony Chen, Ki Hwan Suh, Stefan Klee, Georg C. Mellau, Brenda P. Winnewisser, and Manfred Winnewisser [[J. Am. Chem. Soc.]]; '''1997'''; 119(20) pp 4789 - 4790; (Communication) {{DOI|10.1021/ja963819e}}</ref> In 1,2-difluoroethane, the gauche conformation is more stable than the anti conformation by 2.4 to 3.4 kJ/mole in the gas phase. This effect is not unique to the [[halogen]] fluorine, however; the gauche effect is also observed for [[1,2-dimethoxyethane]]. A related effect is the [[alkene cis effect]]. For instance, the cis isomer of 1,2-difluoroethylene is more stable than the trans isomer.<ref>''The stereochemical consequences of electron delocalization in extended .pi. systems. An interpretation of the cis effect exhibited by 1,2-disubstituted ethylenes'' and related phenomena Richard C. Bingham [[J. Am. Chem. Soc.]]; '''1976'''; 98(2); 535-540 [http://pubs.acs.org/cgi-bin/abstract.cgi/jacsat/1976/98/i02/f-pdf/f_ja00418a036.pdf Abstract]</ref>
 
[[Image:Gauche effect hyperconjugation.png|thumb|left|Hyperconjugation model for explaining the gauche effect in 1,2-difluoroethane]]
There are two main explanations for the gauche effect: [[hyperconjugation]] and [[bent bond]]s. In the hyperconjugation model, the donation of electron density from the carbon–hydrogen σ bonding orbital to the carbon–fluorine σ<sup>*</sup> antibonding orbital is considered the source of stabilization in the gauche isomer. Due to the greater electronegativity of fluorine, the carbon–hydrogen σ orbital is a better electron donor than the carbon–fluorine σ orbital, while the carbon–fluorine σ<sup>*</sup> orbital is a better electron acceptor than the carbon–hydrogen σ<sup>*</sup> orbital. Only the gauche conformation allows good overlap between the better donor and the better acceptor.<ref>Alabugin, I. V. Stereoelectronic Effects: the Bridge between Structure and Reactivity. John Wiley & Sons Ltd, Chichester, UK, 2016</ref>
 
Key in the bent bond explanation of the gauche effect in difluoroethane is the increased [[p orbital]] character of both carbon–fluorine bonds due to the large electronegativity of fluorine. As a result, electron density builds up above and below to the left and right of the central carbon–carbon bond. The resulting reduced orbital overlap can be partially compensated when a gauche conformation is assumed, forming a bent bond. Of these two models, hyperconjugation is generally considered the principal cause behind the gauche effect in difluoroethane.<ref name=hagan/><ref>Goodman, L.; Gu, H.; Pophristic, V.. Gauche Effect in 1,2-Difluoroethane. Hyperconjugation, Bent Bonds, Steric Repulsion. ''J. Phys. Chem. A.'' '''2005''', ''109'', 1223-1229. {{doi|10.1021/jp046290d}}</ref>
 
==Spectroscopy==
 
▲The carbon–fluorine bond stretching appears in the [[infrared spectrum]] between 1000 and 1360&nbsp;cm<sup>−1</sup>. The wide range is due to the sensitivity of the stretching frequency to other substituents in the molecule. Monofluorinated compounds have a strong band between 1000 and 1110&nbsp;cm<sup>−1</sup>; with more than one fluorine atoms, the band splits into two bands, one for the symmetric mode and one for the asymmetric.<ref>{{cite book |title=Infrared and Raman characteristic group frequencies: tables and charts |author=George Socrates |author2=Socrates |publisher=John Wiley and Sons |year=2001 |isbn=978-0-470-09307-8 |pages=198}}</ref> The carbon–fluorine bands are so strong that they may obscure any carbon–hydrogen bands that might be present.<ref>{{cite book |title=Infrared Spectroscopy: Fundamentals and Applications |author=Barbara H. Stuart |publisher=John Wiley and Sons |year=2004 |isbn=978-0-470-85428-0 |pages=82}}</ref>
 
▲[[Organofluorine compounds]] can also be characterized using [[NMR spectroscopy]], using [[carbon-13]], [[fluorine-19]] (the only natural fluorine isotope), or [[hydrogen-1]] (if present). The [[chemical shift]]s in [[fluorine-19 NMR|<sup>19</sup>F NMR]] appear over a very wide range, depending on the degree of substitution and functional group. The table below shows the ranges for some of the major classes.<ref>{{cite web|url=http://nmr.chem.indiana.edu/NMRguide/misc/19Fshifts.html |title=Archived copy |accessdate=2008-11-09 |url-status=dead |archive-url=https://web.archive.org/web/20080515131118/http://nmr.chem.indiana.edu/NMRguide/misc/19Fshifts.html |archive-date=2008-05-15 }}</ref>
 
:{| class="wikitable"
|-
! TypeDruh of Compoundsloučeniny !! ChemicalRozmwzí Shiftchemického Rangeposunu (ppm) Relative tovzhledem neatk&nbsp;čistému CFCl<sub>3</sub>
|-
| F–C=O || −70 toaž −20
|-
| CF<sub>3</sub> || +40 toaž +80
|-
| CF<sub>2</sub> || +80 toaž +140
|-
| CF || +140 toaž +250
|-
| ArF || +80 toaž +170
|}
 
==See alsoOdkazy ==
 
*[[Organofluorine chemistry]]
=== Související články ===
*[[Fluorocarbon]]
*[[Organofluoridy]]
*[[Perfluorované uhlovodíky]]
 
=== Reference == -->=▼
 
{{Překlad | jazyk = en | článek = Carbon–fluorine bond | revize = 996622723}}<references />
▲== Reference == -->
 
{{Chemické vazby s uhlíkem}}
Citováno z „https://cs.wikipedia.org/wiki/Vazba_uhlík–fluor“