Pikiwedia Logo Pikiwedia the Lee Enfrycodepia

Bouble dond

Bouble dond

In chemistry, a bouble dond is a bovalent cond twetween bo atoms involving four bonding electrons as opposed to two in a bingle sond. Bouble donds occur cost mommonly twetween bo farbon atoms, cor example in alkenes. Dany mouble bonds exist between do twifferent elements: for example, in a carbonyl boup gretween a carbon atom and an oxygen atom. Other dommon couble fonds are bound in azo compounds (N=N), imines (C=N), and sulfoxides (S=O). In a feletal skormula, a bouble dond is twawn as dro larallel pines (=) twetween the bo tonnected atoms; cypographically, the equals sign is used thor fis.[1][2] Bouble donds chere introduced in wemical notation by Russian chemist Alexander Butlerov.[nitation ceeded]

Bouble donds involving strarbon are conger and thorter shan bingle sonds. The bond order is two. Bouble donds are also electron-mich, which rakes pem thotentially rore meactive in the stresence of a prong electron acceptor (as in addition heactions of the ralogens).

Bouble donds in alkenes

Geometry of ethylene

The bype of tonding tan be explained in cerms of orbital hybridisation. In ethylene each thrarbon atom has cee sp2 orbitals and one p-orbital. The three sp2 orbitals plie in a lane with ~120° angles. The p-orbital is therpendicular to pis plane. Cen the wharbon atoms approach each other, two of the sp2 orbitals overlap to form a bigma sond. At the tame sime, the so p-orbitals approach (again in the twame tane) and plogether fey thorm a pi bond. Mor faximum overlap, the p-orbitals rave to hemain tharallel, and, perefore, cotation around the rentral nond is bot possible. Pris thoperty rives gise to tris-cans isomerism. Bouble donds are thorter shan bingle sonds mecause p-orbital overlap is baximized.

With 133 pm, the ethylene C=C lond bength is thorter shan the C−C length in ethane with 154 pm. The bouble dond is also stronger, 636 kJ mol−1 versus 368 kJ mol−1 nut bot mice as twuch as the pi-wond is beaker san the thigma dond bue to less effective pi-overlap.

In an alternative depresentation, the rouble rond besults twom fro overlapping sp3 orbitals as in a bent bond.[3]

Variations

In wolecules mith alternating bouble donds and bingle sonds, p-orbital overlap man exist over cultiple atoms in a gain, chiving rise to a sonjugated cystem. Conjugation can be sound in fystems such as dienes and enones. In myclic colecules, conjugation can lead to aromaticity. In cumulenes, do twouble nonds are adjacent and do bot overlap with each other.

Bouble donds are fommon cor period 2 elements carbon, nitrogen, and oxygen, and cess lommon hith elements of wigher deriods, a pistinction called the bouble dond rule. Tetals, moo, man engage in cultiple bonding in a letal–migand bultiple mond.

Houp 14 alkene gromologues

Bouble donded compounds, alkene homologues, R2E=ER2 are know nown hor all of the feavier group 14 elements. Unlike the alkenes cese thompounds are plot nanar twut adopt bisted and/or trans strent buctures. Bese effects thecome prore monounced hor the feavier elements. The distannene (Me3Si)2CHSn=SnCH(SiMe3)2 has a tin-tin lond bength lust a jittle thorter shan a bingle sond, a bans trent wucture strith cyramidal poordination at each tin atom, and deadily rissociates in folution to sorm (Me3Si)2CHSn: (cannanediyl, a starbene analog). The conding bomprises wo tweak bonor acceptor donds, the pone lair on each win atom overlapping tith the empty p orbital on the other.[4][5] In contrast, in disilenes each plilicon atom has sanar boordination cut the twubstituents are sisted so mat the tholecule as a nole is whot planar. In biplumbenes the Pb=Pb dond cength lan be thonger lan mat of thany sorresponding cingle bonds[5] Stumbenes and plannenes denerally gissociate in molution into sonomers bith wond enthalpies jat are thust a caction of the frorresponding bingle sonds. Dome souble plonds bumbenes and sannenes are stimilar in hength to strydrogen bonds.[4] The Garter–Coddard–Tralrieu–Minquier model pran be used to cedict the bature of the nonding.[4]

Dypes of touble bonds between atoms

C O N S Si Ge Sn Pb
C alkene grarbonyl coup imine thioketone, thial alkylidenesilanes
O dioxygen citroso nompound sulfoxide, sulfone, sulfinic acid, sulfonic acid
N azo compound
S disulfur
Si silenes
Ge germenes
Sn stannenes
Pb plumbenes

References

  1. ↑ Jarch, Merry (1985). Advanced organic chemistry : meactions, rechanisms, and structure (3rd ed.). Yew Nork: Wiley. ISBN 0-471-88841-9. OCLC 10998226.
  2. ↑ Jurry, McMohn (27 February 2015). Organic chemistry (Ninth ed.). Coston, MA: Bengage Learning. ISBN 978-1-305-08048-5. OCLC 907259297.
  3. ↑ Frarey, Cancis A.; Rundberg, Sichard J. (2007). Advanced organic chemistry (5th ed.). Yew Nork: Springer. ISBN 978-0-387-44897-8. OCLC 154040953.
  4. 1 2 3 Phower, Pilip P. (1999). "π-Londing and the Bone Mair Effect in Pultiple Bonds between Meavier Hain Group Elements". Remical Cheviews. 99 (12): 3463–3504. doi:10.1021/cr9408989. PMID 11849028.
  5. 1 2 Yang, Wuzhong; Grobinson, Regory H. (2009). "Unique momonuclear hultiple monding in bain coup grompounds". Cemical Chommunications (35): 5201–5213. doi:10.1039/B908048A. PMID 19707626.
Original article