I-hybridization nezibopho ze-sigma ne-pi: ama-orbital angemuva kwesimo semolekyuli

Izibopho njengama-orbital ahlanganayo

I-valence bond theory ichaza isibopho se-covalent njengama-electron amabili anama-spin aphambene endaweni lapho ama-orbital ama-athomu amabili ehlangana khona. Ukuhlangana kuqoqa ukuminyana kwama-electron phakathi kwama-nucleus, lapho kuwaheha womabili. Ukuhlangana okukhulu ngokuvamile kusho isibopho esiqinile.

Ukuhlangana kungenzeka ngezindlela ezimbili. Esibophweni se-sigma (σ), ama-orbital ahlangana ngamakhanda, eduze komugqa ohlanganisa ama-nucleus, ngakho ukuminyana kwama-electron kukhulu kakhulu kuleyo eksisi. Esibophweni se-pi (π), ama-orbital amabili e-p ahambisanayo ahlangana eceleni nangeceleni, ngakho ukuminyana kuphezulu nangaphansi kwe-eksisi, ne-nodal plane equkethe i-eksisi. Sonke isibopho esisodwa siyisibopho se-σ.

Kungani ama-orbital e-2s ne-2p e-carbon kufanele axubane

Ama-orbital e-valence e-carbon ayi-2s eyodwa ne-2p ezintathu. Ama-orbital amathathu e-p abheke eduze no-x, y no-z, ku-90° komunye nomunye. Ukube izibopho ezine ze-C–H ze-methane bezizisebenzisa ngqo, izibopho ezintathu bezizoba ku-90° kanti esisodwa sibe sihlukile. Kunalokho, zonke izibopho ezine ku-CH₄ ziyafana futhi zihlukene ngo-109.5°.

I-hybridization iyakuxazulula lokhu. Ukuhlanganisa ngezibalo i-orbital ye-2s nawo wonke ama-orbital amathathu e-2p kunikeza ama-hybrid orbital amane alinganayo e-sp³ abheke emakhoneni e-tetrahedron. Inani lama-hybrid orbital lihlala lilingana nenani lama-orbital e-athomu axutshiwe. I-orbital ngayinye ye-sp³ ine-lobe eyodwa enkulu ehlangana kahle ne-orbital ye-1s ye-hydrogen, yingakho ama-hybrid orbital akha izibopho ze-σ eziqinile.

Ukunikeza i-hybridization kusuka enombolweni ye-steric

I-hybridization ilandela inani lama-electron domain azungeze i-athomu, inombolo yayo ye-steric evela ku-VSEPR. Amabhangqa amodwa abalwa njengama-domain, futhi isibopho esiphindaphindiwe sibalwa kanye. Uma usuyazi inombolo ye-steric, i-hybridization isinqunyiwe.

Amabhangqa amodwa nawo athatha ama-hybrid orbital futhi aphushela izibopho ukuthi zisondelane. I-OpenStax Chemistry 2e (Isigaba 8.2) inikeza u-107.3° we-engeli ye-H–N–H ku-ammonia no-104.5° we-H–O–H emanzini, kokubili kuyi-sp³ nama-engeli ezibopho angaphansi kuka-109.5° ofanele.

• Inombolo ye-steric 2: sp, linear, 180°. I-s eyodwa ne-p eyodwa ziyaxubana, kusale ama-orbital e-p amabili angenayo i-hybridization. I-orbital ngayinye ye-sp inohlamvu lwe-s olungu-50%.
• Inombolo ye-steric 3: sp², trigonal planar, 120°. I-s eyodwa ne-p ezimbili ziyaxubana, kusale i-orbital eyodwa ye-p eme mpo epulanini. Uhlamvu lwe-s olungu-33%.
• Inombolo ye-steric 4: sp³, tetrahedral, 109.5°. I-s eyodwa ne-p ezintathu ziyaxubana, kungasali lutho. Uhlamvu lwe-s olungu-25%.
• Izinombolo ze-steric 5 no-6 zivame ukubhalwa ngokuthi sp³d no-sp³d², njengaku-OpenStax. Zithathe njengamalebula ejiyomethri; bheka imikhawulo engezansi.

Izibopho eziphindwe kabili neziphindwe kathathu njenge-sigma kanye ne-pi

Ku-ethylene, H₂C=CH₂, i-carbon ngayinye inama-domain amathathu futhi iyi-sp². Ama-orbital amathathu e-sp² akha izibopho ze-σ kuma-hydrogen amabili nakwenye i-carbon. Ama-orbital e-p asele kuma-carbon amabili ayahambisana futhi ahlangana eceleni nangeceleni ukwakha isibopho se-π. Ngakho isibopho esiphindwe kabili siyisibopho se-σ esisodwa kanye nesibopho se-π esisodwa. Isibopho esiphindwe kathathu, njengaku-acetylene, HC≡CH, siyisibopho se-σ esisodwa kanye nezibopho ze-π ezimbili, ezenziwe ngamabhangqa amabili ama-orbital e-p angenayo i-hybridization ame mpo komunye nomunye kuma-carbon e-sp.

Isibopho se-π sichaza ukuthi kungani izibopho eziphindwe kabili zingazungezi ngokukhululeka. Ukusonta uhlangothi olulodwa ngo-90° kungenza ama-orbital e-p ame mpo futhi kwephule ukuhlangana kwe-π. Yingakho i-cis-2-butene ne-trans-2-butene ziyizinhlanganisela ezihlukene ezingaguquki zibe ngomunye nomunye ezingeni lokushisa legumbi, kanti izinhlangothi ezimbili zesibopho esisodwa se-C–C zizungeza kalula.

Izibonelo ezisebenzile: ukubala izibopho ku-acrylonitrile naku-aspirin

Ukubala izibopho ze-σ ne-π, dweba isakhiwo se-Lewis esiphelele, kuhlanganise ne-hydrogen ngayinye. Bese umugqa ngamunye wesibopho unikela ngesibopho se-σ esisodwa ncamashi, isibopho ngasinye esiphindwe kabili sengeza isibopho se-π esisodwa, futhi isibopho ngasinye esiphindwe kathathu sengeza ezimbili.

Isibonelo esisebenzile 1. I-acrylonitrile, H₂C=CH–C≡N, esetshenziselwa ukwenza imicu ye-acrylic. Izibopho ze-σ: ezintathu ze-C–H, esisodwa ku-C=C, esisodwa ku-C–C nesisodwa ku-C≡N, isamba esingu-6. Izibopho ze-π: esisodwa ku-C=C nezimbili ku-C≡N, isamba esingu-3. I-hybridization: womabili ama-carbon esibopho esiphindwe kabili anama-domain amathathu futhi ayi-sp²; i-carbon ye-nitrile inama-domain amabili futhi iyi-sp; i-nitrogen, ene-domain yesibopho eyodwa nebhangqa elilodwa, nayo iyi-sp. Njengokuhlola, ama-electron e-valence angu-3(4) + 3(1) + 5 = 20: izibopho ezingu-9 ziphatha angu-18, kanti ibhangqa elilodwa le-nitrogen liphatha amanye angu-2.

Isibonelo esisebenzile 2. I-aspirin, C₉H₈O₄, idwetshwe nezibopho eziphindwe kabili ezishintshanayo endandathweni ye-benzene. Izibopho ze-σ: ezingu-6 ze-C–C endandathweni, ezingu-4 ze-C–H zendandatho, nezingu-4 eqenjini le-carboxylic acid kanye nesixhumanisi salo nendandatho (i-C–C yendandatho, C=O, C–O no-O–H), nezingu-7 eqenjini le-ester (i-C–O yendandatho, O–C, C=O, C–CH₃ nezintathu ze-C–H). Lokho kunikeza izibopho ze-σ ezingu-6 + 4 + 4 + 7 = 21. Izibopho ze-π: ezingu-3 endandathweni no-1 ku-C=O ngayinye, ezingu-5 sezizonke. Hlola: i-aspirin inama-athomu angu-21 nendandatho eyodwa, futhi noma yisiphi isakhiwo esixhunyiwe sinezibopho ze-σ ezingu-(ama-athomu − 1 + izindandatho), 21 − 1 + 1 = 21. Ukubala ama-electron nakho kuyasebenza: izibopho ezingu-26 ziphatha ama-electron angu-52, ama-oxygen amane aphatha amabhangqa amodwa ayisishiyagalombili, noma ama-electron angu-16, futhi 9(4) + 8(1) + 4(6) = 68. Ama-carbon ayisishiyagalombili ayi-sp²; i-carbon ye-methyl kuphela eyi-sp³.

Isibopho se-pi siqine kangakanani uma siqhathaniswa nesibopho se-sigma?

Amandla ezibopho amaphakathi kuTafula 7.3 le-OpenStax Chemistry 2e akhombisa ukuthi ukwengeza izibopho phakathi kwama-athomu amabili kunikeza inzuzo encipha njalo. Ezibophweni ze-carbon–carbon: C–C, 1.54 Å no-345 kJ/mol; C=C, 1.34 Å no-611 kJ/mol; C≡C, 1.20 Å no-837 kJ/mol.

Isibonelo esisebenzile 3. Ukususa kunikeza amandla alinganiselwe esibopho ngasinye se-π esengeziwe. Isibopho sokuqala se-π sengeza u-611 − 345 = 266 kJ/mol, kanti esesibili sengeza u-837 − 611 = 226 kJ/mol. Kokubili kuncane kuno-345 kJ/mol wesibopho se-σ se-C–C, ngoba ukuhlangana eceleni nangeceleni kubuthaka kunokuhlangana ngamakhanda. Isibopho esiphindwe kabili siqine ngokuphindwe ka-1.77 kuphela kunesibopho esisodwa, hhayi ngokuphindwe kabili. Isibopho se-π esibuthaka yingxenye ephukayo ekusabeleni kokwengeza, yingakho ama-alkene engeza i-Br₂ ne-HBr kalula, ne-H₂ lapho kukhona i-catalyst yensimbi. Thatha le mihlukano njengokulinganisela; amandla ezibopho amaphakathi ahlanganisa amanani avela kumamolekyuli amaningi ahlukene.

Ama-electron e-pi asakazekile nemikhawulo yama-hybrid orbital

Ku-benzene, C₆H₆, yonke i-carbon iyi-sp² futhi ine-orbital eyodwa ye-p engenayo i-hybridization eme mpo endandathweni. Ama-orbital e-p ayisithupha ahambisanayo ahlangana ezungeza yonke indandatho, ngakho ama-electron e-π ayisithupha asakazeke kuyo yonke indandatho kunokuba aboshelwe ezibophweni ezintathu eziphindwe kabili. Zonke izibopho eziyisithupha ze-C–C zinobude obufanayo, phakathi kobude obujwayelekile besibopho esisodwa nesiphindwe kabili.

I-resonance ihlela kabusha ama-electron e-π namabhangqa amodwa, ingalokothi ihlele izibopho ze-σ, ngakho kuma-athomu afana nama-carbon e-benzene noma yisiphi isakhiwo esivumelekile sinikeza i-hybridization efanayo; i-OpenStax isho leli phuzu ngokucacile nge-benzene. Qaphela nge-athomu ebhangqa layo elilodwa liba yisibopho se-π kwesinye isakhiwo, njenge-nitrogen ku-amide: inani lama-domain ayo liyashintsha phakathi kwezakhiwo, futhi ijiyomethri yayo eyisicaba ebonwayo ikhombisa ukuthi iyi-sp². Ukusakazeka kuyindawo lapho i-valence bond theory iba nzima khona, futhi i-molecular orbital theory inikeza incazelo ecace kakhudlwana.

I-valence bond theory ibhangqa yonke i-electron esibophweni noma ebhangqeni elilodwa, ngakho ibikezela ukuthi i-O₂ ayinawo ama-electron angabhangqiwe. I-oxygen eketshezi empeleni iyahehwa uzibuthe, okukhombisa ukuthi i-O₂ inama-electron angabhangqiwe. I-molecular orbital theory yakha ama-orbital angawemolekyuli yonke. I-bond order iyingxenye yomehluko phakathi kwama-electron akuma-orbital e-bonding ne-antibonding. Ku-O₂, ama-electron e-valence angu-12 anikeza angu-8 e-bonding nangu-4 e-antibonding, ngakho i-bond order (8 − 4)/2 = 2. Ama-electron amabili okugcina athatha ama-orbital amabili ahlukene e-π* anama-spin ahambisanayo, okuchaza i-paramagnetism. Ku-N₂, (8 − 2)/2 = 3, okuhambisana nesibopho sayo esiphindwe kathathu.

Amaphutha e-hybridization nendlela yokuwabamba

Amaphutha amaningi avela ekweqeni isakhiwo se-Lewis noma ekubaleni kabi ama-domain. Bala izibopho ze-σ namabhangqa amodwa ku-athomu kuqala; i-hybridization ilandela lokho kubala kuphela.

• Ukubala izibopho ze-π enombolweni ye-steric. Izibopho ze-σ namabhangqa amodwa kuphela okubalwa njengama-domain.
• Ukukhohlwa amabhangqa amodwa, okwenza i-nitrogen ku-NH₃ ibukeke iyi-sp² esikhundleni se-sp³.
• Ukubala isibopho esiphindwe kabili njengezibopho ezimbili ze-σ. Sonke isibopho esiphindwe kabili siyi-σ eyodwa ne-π eyodwa.
• Ukushiya ama-hydrogen lapho ubala izibopho ze-σ kufomula ye-skeletal noma ehlanganisiwe.
• Ukucabanga ukuthi yonke i-carbon enesibopho esiphindwe kabili iyi-sp². I-carbon emaphakathi ye-CO₂, enezibopho ezimbili eziphindwe kabili, inama-domain amabili futhi iyi-sp.
• Ukukholelwa ukuthi isakhiwo se-resonance sishintsha i-hybridization ye-athomu. I-resonance ihambisa ama-electron e-π, hhayi izibopho ze-σ.